Categories
Cold War Soviet Prototypes

Object 911

Soviet Union (1963-1964)
Infantry fighting vehicle – 1 prototype

The evolution of warfare and technologies in the years following the conclusion of the Second World War had a major impact on the way warfare would be conducted in the future. The appearance and proliferation of nuclear weapons led to the need for protection from nuclear fallout and radiation being a major requirement for combat vehicles meant to operate in a battlefield that could likely be saturated with tactical nuclear strikes. The truck-borne infantry of the past was also increasingly sidelined for infantry in armored personnel carriers, which could keep up with armored formations and allow for highly-mobile infantry protected from small arms fire and shell splinters. Following these conclusions, work began on a vehicle in the Soviet Union which would not only transport infantry while keeping up with tanks, but also provide protection from nuclear fallout and combat capabilities needed to supplement tanks and provide support to infantry. One of the prototypes created in the 1960s to fulfill such a task was Volgograd Automotive Plant’s Object 911.

The Object 911 prototype, showing its most unusual feature: the presence of both wheels and tracks. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The Infantry of a Mechanized, Nuclear Age

After years of development, the United States detonated the first nuclear warheads in 1945, first over the New Mexico desert and later over the Japanese cities of Hiroshima and Nagasaki. The Soviet Union had laid a keen eye on the development of this new type of weapon, which promised unprecedented levels of destructive powers achieved by a single bomb. On 29th August 1949, the Soviet Union followed suit by detonating its first atomic warhead in the RDS-1 test, years ahead of American and British expectations.

In the following years, the United States and the Soviet Union, soon followed, to a much lower extent, by the United Kingdom, and later France and the People’s Republic of China would pursue massive buildups of their nuclear arsenals. By 1960, the United States’ stockpile had already exceeded 15,000 weapons. The Soviet buildup was, at the time, much slower, but at more than 1,500 warheads, it would already be enough to cause massive destruction.

The explosion of the RDS-1 test. Source: dissolve.com

With the massive buildup of nuclear stockpiles, the perceived roles of nuclear weapons also evolved. The weapons would be used in strategic strikes against enemy cities, production, and logistical centers, as had been originally intended and tested against Japan in 1945, but new potential targets were soon considered. Value was also found in ‘tactical’ nuclear missiles and bombs, which would be used on a much smaller scale, against enemy troop concentrations, supply depots, or ways of communications on the frontline. This newfound purpose of nuclear weapons, coupled with the increasing realization of the major health effects of nuclear radiation, led to the understanding that many aspects of conventional warfare would find themselves struggling to find any purpose on this new, nuclear battlefield.

This was supplemented by the fact that, in the 1950s, the USSR considered a conflict in mainland Europe was a likely occurrence, as demonstrated by the heavy tensions of the late 1940s and early 1950s. At this point in time, and up to the early 1960s, while the Soviet Union did have nuclear weapons, the means of delivery were far less developed than those of the United States. While the United States had a large fleet of strategic bombers that could realistically become a threat to many Soviet cities, the USSR struggled to establish an equivalent force. The Soviets wanted to rely on a submarine fleet to counter this, but it was only starting to build itself up in the late 1950s, and NATO could rely on extensive naval forces. The only aspect where the Soviet Union had a somewhat reliable nuclear force was in its ground forces. Between the use of tactical nuclear weapons in the Soviet Army and the otherwise nuclear superiority of NATO, the Soviet Army expected to be forced to fight on a heavily irradiated battlefield. Many of the aspects of the post-WW2 Soviet Army could not be expected to operate in such an environment.

One of the prime examples was that of infantry moved by trucks, largely open vehicles that could hardly be protected from nuclear radiation and fallout. Armored vehicles, in comparison, were already often enclosed, and making them able to protect their crews from nuclear radiation, as well as chemical and biological threats, was a viable option. This suddenly highly increased the value of armored personnel carriers. While already vehicles with significant potential and increasing in popularity since the conclusion of the Second World War, they appeared as perhaps the most viable option to continue to make infantry relevant. Not only would they be able to keep up with armored vehicles and, in this way, considerably ease combined arms operations, but they would also protect infantry from small arms fire, and, perhaps even more importantly, from nuclear radiation. Because of this reason, after the rise of power of Khrushchev in the Soviet Union from 1953 onward, considerable emphasis was put on adapting the Soviet Army for nuclear warfare, and outfitting Soviet infantry with better vehicles for this purpose than mere trucks.

In the Soviet Union, the idea would be pushed further though. Rather than design pure troop carriers which would typically be armed with just a machine gun, the idea of a vehicle that could not only keep up with tanks while transporting infantry but also provide valuable combat support to both arose. The main recipients of this envisioned vehicle were to be motor rifle regiments, though it would in general be widespread through the Soviet Army.

The BMP Concept

The concept of this new type of vehicle was popularized in the late 1950s in the Soviet Union, though some similar concepts were being developed in other countries, notably the West German Schützenpanzer Lang HS.30.

The idea of the BMP ( Боевая Машина Пехоты, which translates to Infantry Fighting Vehicle) was to create a vehicle that would provide CBRN (Chemical, Biological, Radiological, and Nuclear) protection to the troops it carried. This was at first the factor separating the BMP from APCs like the BTR series, which at the same time included a significant amount of non-CBRN protected vehicles, such as open-topped BTR-40s, BTR-152s, and BTR-50s.

Beyond this nuclear protection aspect, the BMP was also meant as a vehicle that would have the mobility and armament necessary to offer support to tanks. This meant it should be able to engage many targets, from tanks to various armored fighting vehicles, to infantry and field fortifications. Another aspect that was desired was superior mobility, with the crossing of water obstacles being a major factor. There are many major rivers in Europe, and bridges could not be relied on in a very destructive major conflict on the continent. It was also hoped that the infantry would be able to fight from the inside of the vehicle itself, not necessarily having to dismount, another concept brought forward by the prospect of an irradiated battlefield.

The first task would be accomplished by the presence of firing ports from which the troops could fire their weapons. The idea of bow machine guns operated by the infantry dismounts (dismounts is a term widely used to refer to the infantry carried inside or on top of Soviet vehicles), rather than the crew of the vehicle itself, was also considered. Because of this firing port requirement, the position of the infantry towards the front and center of the vehicle, rather than the rear, was preferred. Enemy targets would typically be found towards the front and sides of the vehicle, rather than the rear.

Firepower-wise, the main purpose envisioned with the BMP was the ability to defeat enemy anti-tank capabilities as well as provide fire support to dismounts. This would translate into the main armament that could take out infantry positions equipped with recoilless rifles or anti-tank guided missiles as well as lightly armored vehicles. A number of armaments of various calibers were considered for this purpose. This included main guns firing 57, 73, or 76 mm shaped charges projectiles, or 30, 37, or 45 mm autocannons. Eventually, the 73 mm 2A28 Grom low-pressure smoothbore gun would be chosen. This main gun was to be supplemented with one or several 7.62 mm machine guns for anti-infantry duties. Since there was a high risk of encountering enemy tanks, while following friendly tanks, an anti-tank missile launcher, with 4 to 6 missiles, was also required and would have to offer the possibility of being fired from inside the vehicle, with hatches closed.

Protection-wise, the vehicle was to provide protection from heavy machine guns, such as the 12.7 mm/.50 cal Browning M2HB, or possibly even 20 or 23 mm autocannons, on the frontal arc. On the sides and rear, protection levels were to allow the vehicle to withstand 7.62 mm rounds, as well as artillery shell splinters. Heavier armor was impractical due to amphibious and air-transportability needs.

A very significant aspect of the protection was the one from NBC (Nuclear, Biological, Chemical) threats. The vehicle was to provide an enclosed environment in which the crew and dismounts would be able to operate, even on a highly irradiated battlefield. This would translate into high efforts being taken to seal the vehicle and fit it with an air filtering system as well as an anti-radiation lining. These design requirements would translate into the vehicles being the first troop carrier designs taking into account nuclear radiation protection.

By the late 1950s, Volgograd was already producing a tracked, amphibious armored personnel carrier in the form of the BTR-50. As designed, the BTR-50 was an open-topped vehicle, which would entirely prohibit any kind of radiation protection. By the late 1950s, this had been remedied by the BTR-50PK modification, which incorporated an enclosed roof.

BTR-50P APCs at the Red Square on 7th November 1961. Note their open roof; a closed roof version, the BTR-50PK, would later be introduced Source: Topwar.ru
The BTR-60 also started out as an open-topped vehicle. Source: soldat.pro

Interestingly, whilst the Object 750 prototype had 2 firing ports per side for the dismounts, the serial BTR-50P did not.

One of the requirements for the BMP was to allow the whole infantry squad to engage targets from the inside.

However, it was thought that the IFV would provide far better-fighting capabilities, as well as protection for the infantry in an irradiated environment. Also, the BMP would allow for dismounts to engage from inside the vehicle, while a BTR-50 could really only transport the infantry or cargo through the irradiated terrain, but the troopers could not even exit and fight safely.

In terms of mobility, the vehicle’s main objective was to be more mobile than tanks, which meant a relatively high maximum speed but, most importantly, very good off-road capacities. The vehicle was also required to be amphibious to allow the crossing of rivers and marshes even without bridges. These requirements resulted in weight and size constraints inherent in all types of Soviet and Russian APCs and IFVs.

Lastly, the vehicle was to be small and light enough to be air-transportable, though it was not meant to be dropped from a plane as an airborne vehicle. It was also desirable to create a vehicle that would be as simple and easy to produce as possible. It was hoped it could then be produced in large numbers with relative ease, as well as form the base for a large family of vehicles that would use its components.

A formal call for design proposals following these requirements was issued by the GBTU (The General Armored Directorate, the service in charge of armored vehicles procurement) on 22nd October, 1960. The requirements were finalized in September 1961 and eventually sent to a large number of design bureaus. Initially, the Main Artillery Directorate, which issued the requirements, called for an 11-12 tonnes vehicle that would feature a crew of 2 and transport 6 to 8 dismounts.

At that time, three different views existed on how to design the future IFV. One was to create a new, wheeled vehicle, sometimes using some pre-existing technology. The second was to create the vehicle based on a pre-existing chassis. The third was to create an all-new, tracked vehicle. One of the designers which were issued the requirements was VgTZ (Volgorgadskii Traktornii Zavod, Volgograd Tractor Plant, the former STZ/Stalingrad Tractor Plant). Eventually, this relatively large design bureau would offer two different variants. The first would be based on VgTZ’s PT-76 amphibious tank, the Object 914 (VgTZ was attributed numbers in the 900s for the designation of its prototypes). The other would be a completely new vehicle, which used a tracked configuration, though with a number of unique elements; this would be Object 911.

Volgograd’s Object 911

The pilot projects for vehicles from different manufacturers were first presented at a meeting in November 1960. At this point, some of the characteristics of the future BMP were still uncertain. For example, the possibility of using a 14.5 mm machine gun as main armament was still being considered.

The Volgograd design bureau started elaborating various solutions following the November 1960 meeting. Their attempts at creating a BMP would typically, as had been with the Object 914, use a lot of elements from previous projects, in this case the PT-76 and the Object 906B, two light tank designs. The first was adopted and mass-produced, the second stayed on the drawing board.

Configurations studied by Volgograd generally used a rear engine configuration, though there was a draft project with a front engine and rear transmission, as on the PT-76 and related vehicles. An early set of plans for the Object 911 dated 1962 envision a vehicle featuring a two-man turret and a dismount compartment for six dismounts sitting in three rows of two. This configuration would be entirely changed before the vehicle would enter the prototype stage.

The early configuration of the Object 911, with a six-man dismount complement present in three rows of two and a two-man turret. By the time the vehicle reached prototype, this would be replaced by an eight-man compartment and a one-man turret stage. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The draft project of the Object 911 was developed at VgTZ in 1963, and presented to the State Committee for Defense Technology (GKOT, Russian: ГКОТ, Государственный комитет по оборонной технике), which considered it and allowed for the production of a prototype on August 9th, 1963.

The prototype of the Object 911 was built in the same year under the supervision of the head engineer, I.V. Gavalov. The prototype went to the comparative trials in 1964, alongside several other prototypes of the BMP.

The prototypes tested largely varied in terms of configurations, and included the fully tracked Objects 914 and 765, the wheeled Object 1200, and the convertible Object 911. Usually, convertible designs used the wheels as the main means of motion and lowerable tracks for moving off-road. The Object 911 used the opposite configuration using retractable wheels for traveling on roads, a peculiar feature.

The Object 911’s Design

Hull

The overall design of the Object 911’s hull was a rectangular, welded steel box. Like most Soviet amphibious vehicles of the era, it featured a bow-shaped frontal part for the purpose of improving the vehicle’s hydrodynamic characteristics, further perfected by a retractable trim vane at the front of the hull. The whole upper front/roof plate was angled at a very steep angle, highly improving protection over its frontal arc. The Object 911 had a fairly low profile, with a total height of 2,068 mm, including the turret. According to Domestic Armored vehicles vol 3, at some point, the height of the hull was increased to 1,200 mm.

A ¾ view of the Object 911 prototype on its tracks. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
The eventual configuration of the crew and dismounts on the Object 911. Only the driver, to the center-front of the vehicle, and the gunner/loader/commander, in the turret, are crewmembers. The remaining eight are dismounts. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

Legend: М-В – механик-водитель, driver; Н-О – наводчик-оператор, gunner-operator/vehicle commander; С – стрелок, rifleman, dismount; К – командир, infantry section commander; П – пулеметчик, machine gunner

Apparently the section commander also acted as a second machine gunner, as the Otechestvennye boevye mashiny vol. 3 mention ‘two hatches for the machine gunners’ (page 446)

The Object 911 used a configuration where the crew and dismount compartment were concentrated at the front and center of the vehicle. The vehicle had a crew of two: a driver, who sat in the front center of the hull; and a gunner/commander, who sat behind in the left part of the centrally-mounted turret.

The eight dismounts were present in a symmetric configuration. Two were in front of the turret, one on each of the driver’s sides, and would presumably operate the squad’s machine guns. Six sat just behind the turret. Each dismount had a firing port in the sides of the vehicle, so they could fire their weapons from the inside of the hull. Considering the placement of the firing ports, four on each side of the vehicle, they would be able to create an arc of fire over about the front two thirds of the vehicle.

Each of the dismount positions featured an episcope. The driver’s post appears to have featured three, one to the front and one to each side. The driver would steer the vehicle via a steering wheel. The vehicle featured two headlights, mounted to the front sides of the bow. There was a ventilator just to the rear of the driver’s hatch.

A top view of the Object 911 at Kubinka, showing the front driver’s port as well as the ventilator located right behind it. Source: skylancer7441’s archive
A top front view of the Object 911. Observe the five episcopes present for the dismounts to the sides of the vehicle as well as the two hatches on the front sides of the hull roof. Source: skylancer7441’s archive
A close-up on one of the two dismount’s front-sides hatches. Exiting through these would be highly dangerous when under fire, and the larger hatch located behind the turret would likely be preferred outside of emergency evacuations. Source: skylancer7441’s archive

The vehicle’s engine was mounted at the rear of the vehicle, which would typically make hatch placement harder on an infantry fighting vehicle. The use of a fairly small engine on the Object 911 allowed for a quite peculiar hatch design. The center of the vehicle to the rear of the turret was lowered in comparison to the side ‘flaps’, and a large hatch was located there, opening upward and locking at about a 90° angle. Six of the dismounts were to exit through this hatch. It was hoped that it was wide enough for two dismounts to evacuate at a time. The dismounts would then jump out of the vehicle, which would be a fairly short 0.75 m to 1.10 m drop to the ground. This configuration was far from ideal, as the dismounts would prove very vulnerable if forced to exit when the vehicle was under fire. However, there were not many safer options for a vehicle with a rear engine compartment. Despite these potential considerations, this very configuration would be adopted for the BMD series of vehicles, and eventually even make its way to the BMPs with the BMP-3.

As for the driver and gunner, they each had a dedicated hatch they could exit the vehicle through. Furthermore, there were also two hatches on the front sides of the turret. These would be used for the two front dismounts to exit the vehicle, the squad commander and machine gunner.

The combat weight of the Object 911 was 12.07 tonnes. Length was 6.735 m, width 2.940 m, and height 2.040 m including the turret, presumably at the highest ground clearance. The average ground pressure was 0.46 kg/cm².

The Object 911 had the same level of protection as its main competitor, the Object 765.

A top rear view of the Object 911, with the exit hatch the dismounts would use opened. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
A side view of the Object 911. Four firing ports can be seen towards the front half of the vehicle. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The vehicle featured an R-123 high/very high frequency radio transceiver, which at the time was a new introduction in Soviet vehicles, which could assure communications at ranges up to 20 km on two bands. It was coupled with an internal R-124 intercom system for communications between the gunner/commander and driver.

The R-123 radio station. Source: pinterest
An R-124 intercom system dismounted from a vehicle. Source: http://pribor.zp.ua/

Engine and Hydrojets

An UTD-20 engine, which was widely used in Soviet infantry fighting vehicles and light tank prototypes from the 1960s onward. Source: https://geek-tips.imtqy.com/

The engine used in the Object 911 was common to all the vehicles presented in the program. This was the UTD-20 diesel engine. It produced 300 hp at 2,600 rpm and reached its maximum torque output of 981 N.m at 1,500 to 1,600 rpm. Without any fuel or oil, the engine weighed 665 kg, and had a consumption of 175 to 178 grams of fuel per hp an hour.

The UTD-20 engine was fairly limited in size, which was a major positive factor for installation in the various BMP prototypes. On the Object 911, this allowed for the engine block to be placed in the rear of the vehicle despite the large central lowered section where the dismounts would exit from. The transmission and drive sprocket were placed at the rear of the vehicle as well. The mechanical transmission had a two-disc main friction clutch and a two-shaft five-gears gearbox which would be actioned by the driver. The gearbox included two clutches and two coaxial planetary gearboxes.

A rear view of the Object 911. The two hydrojets present on the ‘flaps’ of the vehicle can be seen. One can also spot spare track links on the central hatch. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

In addition to this engine and transmission, the Object 911 also featured two hydrojets. These were found in the ‘wings’ or ‘flaps’ at the rear of the vehicle. They were taken straight from a previous design of Volgograd Tractor Plant, the PT-76. These hydrojets were powered via a driveshaft with a reducer, linked to the gearbox, and would allow for far quicker movement on water than vehicles using merely tracks or wheels for amphibious crossings.

A view of the propeller of one of the Object 911’s hydrojets, seen thanks to the open hydrojet cover. Source: skylancer7441’s archive

Modern Wheel-Cum-Track?

By far the most uncommon and distinctive features of the Object 911 were to be found in the vehicle’s suspension and drivetrain.

A schematic of Object 911’s drivetrain, showing the locating of the track’s road wheels, idler and sprocket, as well as the four wheels and the steering wheels that commands the movement of the vehicle. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
A front view of the Object 911 at the maximum and minimum ground clearance allowed by the suspension when running on tracks. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
A suspension arm on one of the Object 911’s roadwheels. Source: skylancer7441’s archive

The engineers of Volgograd Tractor Plant experimented heavily with the suspension on Object 911. They settled on a mainly tracked suspension, which was to be used systematically in operational conditions. The vehicle’s tracked suspension used a rear-drive sprocket and a front idler, with five road wheels. The road wheels appear to have been identical to those found on the PT-76, being stamped steel road wheels with reinforcement ribs, and internally hollow to improve buoyancy. Each road wheel was mounted on a suspension arm of which the movement was assured by a pneumatic suspension. The suspension’s height could be adjusted and considerably lowered, with a maximum ground clearance of 426 mm and minimum ground clearance of 96 mm. The tracks themselves were OMSH tracks, made of cast manganese steel and connected by a steel pin, with three connection points. The Object 911 also featured three return rollers: one located towards the front of the second road wheel; the second, or middle one, towards the front of the fourth road wheels; and the last just in front of the drive sprocket. They appear to have been made out of aluminum.

Three photos of the Object 911 on its wheels. These would heighten the silhouette of the vehicle, but seeing as they were meant to be used out of combat, this was not a major issue. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The most unusual aspect of the Object 911’s drivetrain was not the pneumatic, adjustable suspension, the same design as on the Object 906B, but rather the dual drive. Indeed, the Object 911 was not just a tracked vehicle, as it had been designed with a set of four wheels mounted on the internal sides of the tracks. They were located at around the same length as the sprockets and idlers. The wheels could be retracted or extended depending on whether the tracks or road wheels were to be used. This could be done from the inside of the vehicle, with no need to exit, and be performed in three minutes. However, even when fully retracted, the bottom of the wheels would still stick out of the hull bottom by a moderate extent.

The wheels were taken from a pre-existing design. This was not a standard road vehicle design, but rather the K 157-300 designated aviation wheels taken from the Ilyushin Il-14 twin-engine transport aircraft. The main advantage was that aviation wheels were lighter than similar-sized ground vehicle ones, though they were also less sturdy. These wheels had a diameter of 840 mm and a width of 300 mm, and used arched tires. The vehicle used a 4×2 configuration, with the front wheels being used to steer the vehicle when on the wheel drive.

The main advantage envisioned behind these retractable wheels was higher maximum speed and reduced fuel consumption when driving on highway, notably for transfers or movement behind frontlines.

A front view of the Object 911 at a high ground clearance, on tracks. As can be seen, the wheels, even when retracted at their highest point, would not entirely be contained within the hull. This would prove a major issue with the cross-country capacities of the Object 911. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
A view of the rear of the Object 911’s suspension. One can see the rearmost return roller, located just in front of the drive sprocket, as well as one of the retractable wheels, located right behind the last road wheel. Source: skylancer7441’s archive
A close-up of one of the Object 911’s retractable wheels, showing the dimensions of the wheel inscribed on the rim. Source: skylancer7441’s archive

Turret and Armament

All the infantry fighting vehicles of the program used a standardized turret design, which was also present in the vehicle which would be adopted as the BMP-1, the Object 765. This standard design had been created by the Tula KBP Design Bureau and had a 1,340 mm turret ring. It used welded construction from rolled homogeneous armor plates. The turret had a frustoconical design. The turret featured a DGN-3 24 V 300 W motor for rotation, which could rotate at speeds from 0.1º to 20° per second. The gun elevation was powered by another electric motor, the DVN-1 24 V producing 65 W. The gun could elevate or depress at any speed from 0.07º to 6° per second, with maximum elevation angles of -4º to +30°.

Two hatches were present on the turret. There was a large top hatch opening frontwards, locking in an upright position, which the gunner could use to reach out of the turret to observe the surroundings, or to exit the vehicle. There was a much smaller hatch, located over the gun breech, which, when the gun was fully elevated, would be used to load a missile into the launching rail featured on top of the gun.

A view of the Object 911. The low profile of the turret is apparent. This was both an advantage, as it reduced the silhouette of the vehicle, but also a drawback, as the turret was quite cramped. Source: Бронетанковая Техника via tech.wikireading.ru

A single crewmember was located in the turret sat in the left half. The turret was typically considered to be quite cramped, even though it did not feature a basket and, as such, the crewmember could extend his legs into the hull when stationary. He sat on an adjustable seat that featured a backrest. He had five vision devices. Towards the front, he could observe the battlefield through the 1PN22 combined day-night sight. This sight had two channels, one for day and one for night, which would be toggled by rotating an internal mirror. The gunner would look through the same eyepiece in any case. Using the day channel, the sight had a magnification of 6x and a field of view of 15°. The night channel had a magnification of 6.7x and a field of view of 6°. It had a three-stage light intensifier system that would amplify light by 50,000 to 75,000 times. It also featured vastly simplified lead and range corrections scales in order to ease night firing. The other vision devices were four TNPO-170 episcopes, two on the flanks of the 1PN22 sight in order to provide vision to its sides, and two others on the side of the main hatch.

General schematics of the 2A28 Grom. Source: Tankograd

The main armament of the turret was a 73 mm 2A28 Grom low-pressure smoothbore gun. This was a fairly short gun, with a 2,117 mm tube and 2,180 mm total length. The design was overall made to be very simple and light. For example, it lacked any bore evacuator, and the gun fumes were instead to be evacuated from the turret, which featured a ventilator for this purpose. The gun overall weighed only 115 kg and had an average barrel life of 1,250 rounds. The recoil mechanism of the Grom was contained in an armored sleeve, wrapped around the base of the barrel. The launching rail for the Malyutka missile was placed on top of this sleeve.

Quantities of PG-15V rounds, here captured by Azerbaijan from Armenia during the 2020 Nagorno-Karabakh War. The round was produced in massive quantities, and despite more modern ammunition to fulfill both anti-armor and anti-personnel roles, having been available since the 1970s, it is still widely used. Source: reddit

There was only a single shell available to the 2A28 Grom in the 1960s. This was the PG-15V. It used the PG-9 HEAT (High Explosive Anti-Tank) anti-tank grenade already used by the SPG-9 73 mm recoilless gun, but swapped the original propellant charge with a more powerful PG-15P, which was meant to ensure a longer effective range. The projectile was fin-stabilized and featured a rocket engine towards the rear, with propellant present towards the middle of the grenade. This allowed it to reach a higher speed than would typically be expected from a gun as short as the Grom, with a maximum velocity of 655 m/s.

The explosive charge of the PG-9 grenade was a 322 g explosive mixture which would be equivalent to 515 g of TNT. An advantage of the PG-9 was that it featured a high standoff distance (i.e distance between the shaped charge and tip of the fuze) of 258 mm. In practice, this meant that, upon hitting a target, the jet of molten metal would have a significant length to take shape into a thin, dense jet. The results were a great armor penetration for the time and small size of the gun. The projectile’s armor penetration was officially rated at 300 mm at all ranges. In practice, this was slightly higher, as the official figure was based on the quantity of armor which would be pierced with the shell then having significant post-penetration effects inside. The maximum penetration achieved could vary between 302 and 346 mm, with an average value of 326 mm. In practice, this meant the Grom could quite reliably penetrate any tank operated by NATO in the 1960s.

The shell was not without issues, however. The downside of HEAT projectiles and a very short barrel were an overall low accuracy and high dispersion. The Grom’s PG-15V projectiles were notably very vulnerable to wind. The nominal maximum range of the Grom was of 800 m, but even at this range, only a 34% hit rate was achieved against a T-55 during trials. Although this tank was quite smaller than most NATO tanks, in practice it can still be said a vehicle wielding a Grom would have to get to close ranges to use this gun effectively against armored targets. Additionally, during the 1960s, the PG-15V was the only available shell for the 2A28 Grom. HEAT shells are not purely anti-tank projectiles, and by nature also have some capacities against other targets. They can notably be effective when used against field fortifications and bunkers. However, due to their design focusing on producing a jet of molten metal in one direction, they offer very limited capacities when attempting to fire at infantry in the open. For the vast majority of vehicles, this would fairly easily be dealt with by simply shifting to a high-explosive fragmentation shell, but no projectile of the type would be available for the Grom until 1973.

The 2A28 Grom was fed by an autoloading mechanism. It used a crescent-shaped conveyor which would occupy the 1 to 7 o’clock perimeter of the turret floor. Because the Grom only fired one shell type when the autoloader was created, its design was simplified, as there was no need to be able to cycle shell type. A total of 40 projectiles would be present within the autoloader. These would be all the projectiles carried within the vehicles of the BMP program. They would be fed into the gun to the right of the gunner. The gun elevation needed to be set to 3° each time it was to be loaded. The loading cycle was 6 seconds long. Though it used an autoloader, the 2A28 Grom could also be shifted to manual loading if need be.

Photos of the 7.62 mm PKT machine gun. Source: weaponsystems.net

This 2A28 Grom was supplemented by a 7.62 mm PKT coaxial machine gun. Mounted to the right of the gun, it would effectively be the only reliable means of dealing with infantry in the open. It fed to the right and ejected to the left. The PKT was fed from 250 rounds ammunition boxes and would fire at a cyclic rate of fire of 700 to 800 rounds per minute, at a muzzle velocity of 855 m/s. It would be able to expend two ammunition boxes in quick succession before the barrel would need to be replaced, or at least the firing interrupted for a bit to prevent overheating.

In addition to these two weapons, the turret featured an ‘ace up its sleeve’ when dealing with armor threats at ranges where the Grom would not be accurate. This was a 9M14 Malyutka missile launcher. The missile was located on a launching rail installed on top of the gun. Inside the turret, the gunner had a control box, which would be kept folded under the seat when not in use and be extended to guide the Malyutka when the need to fire it arose.

A Soviet soldier behind a Malyutka in the field. Source: portal-kultura.ru

The Malyutka was a 860 mm long missile, 125 mm in caliber, and with a ‘wingspan’ of 393 mm with its 4 stabilizing fins. Overall, it weighed 10.9 kg, with a 2.6 kg shaped explosive warhead. The missile had a small rocket engine which would allow for a flight speed of 120 m/s. It was rated for firing ranges of 500 to 3,000 m. Due to the slow speed, the flight time to the longest effective range would reach a particularly long 26 seconds. When impacting a target, the 9M14 could be expected to penetrate 400 mm of armor at a flat angle. Once again, this would typically be sufficient to penetrate all NATO armor of the era with relative ease.

Guidance of the Malyutka was assured by wire, which was common for early missiles but also fairly unreliable. The gunner had a control box that featured a button to launch the missile and then a retractable joystick used to steer it. The missile was manually guided all the way through and, as such, the gunner was supposed to fully concentrate on missile guidance during the whole firing process.

The loading of a 9M14M missile onto the launching rail on a BMP-1. During the trials of the Object 911 and other prototypes in 1964, the missile used would have been the baseline 9M14. By the time the BMP-1, formerly the Object 765, would start entering service from 1966 onward, the missile had been replaced by the upgraded 9M14M. The baseline 9M14 would never be issued with the BMP-1. Source: tech.wikireading.ru

As with the Grom, the Malyutka provided significant armor piercing capacities to the Object 911 if it was to hit, but this was far from a given considering the slow speed and manual guidance of the missile. Hit probability on a static tank-sized target was only 20% to 25%. Two missiles were carried within the turret. The vehicle was not supposed to travel outside of combat zones with a missile mounted, and as such these, alongside potentially missiles stored inside the hull (it is unknown whether the Object 911 would have any) were all the vehicle had to contend with. On the plus size, as with the PG-15V, the explosive nature of the Malyutka’s warhead means it could also be fired with good effects on field fortifications and fixed positions. The process of preparing for the firing of a Malyutka, including taking out the control box and loading the missile onto the firing rail, could take from 40 to 55 seconds depending on the skills of the gunner.

Performances

Trials for the Object 911, alongside Objects 19, 914, 765, and 1200 were held in 1964.

A top-rear view of Object 911 during its trials. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

During these, the Object 911 was able to reach a maximum speed of 57 km/h on road when using tracked drive. This was fairly moderate. On water, top speed reached 10.3 km/h thanks to the hydrojets, which is on the higher end of amphibious vehicles of the era.

The use of wheeled drive would highly improve the maximum speed of the Object 911 on roads though. It was recorded at a maximum speed of 108 km/h on a paved road, and had an average cruise speed of 70 km/h on highways using wheeled drive. In addition to the superior maximum speed, the use of wheeled drive also had another major upside. It highly reduced the fuel consumption of the vehicle, to the point where the crossable distance reached a tremendous 1,350 km. In comparison, when driving on tracks on dry, dirt roads, the range would vary from 350 to 500 km. This maximum range advantage could be very significant if large movements had to be undertaken on roads without transporters.

The Object 911 struggling to overcome a slope during its trials. It would eventually succeed in overcoming it, whereas the Object 19 and the Object 1200 failed. Source: Bronya Rossii (Russia’s Armor) Episode 8
The Object 911 moving cross-country during its trials. The vehicle was generally considered to have better off-road mobility than Object 19 and 1200, but was outclassed by Object 914 and Object 765 in this regard. Source: Bronya Rossii (Russia’s Armor) Episode 8

In terms of cross-country capacities, Object 911 was able to cross a 30° degree slope. In practice, it provided better slope crossing capacities than the mostly or fully wheeled Object 19 or 1200. However, cross-country mobility was overall found to be inferior to the fully tracked Object 765 and Object 914.

The Flip Side of the Coin: an Overly Complex and Damaging Drive

When considering the improved road speed and range, one may find the dual drive with wheels featured on the Object 911 to be a major improvement in comparison to other vehicles. It is true that, in theory, the improvements gained in speed and range were considerable, but in practice, these were more than offset by a large quantity of issues with the wheels.

The first was that the wheels, located under the belly of the tank, were typically hard to reach and remove for maintenance. This issue was exacerbated by the fact the aviation wheels used in the Object 911 were more vulnerable to wear and tear in comparison to standard ground wheels and, as such, would need to be maintained or replaced more often when in active use. The wheels were also found to overly complicate the production of the vehicle and make it longer and more expensive to produce. This was once again a major issue, as the goal behind the program was to provide an easy and quick-to-produce vehicle which could be introduced in massive numbers.

Object 911 during the process of switching from tracked to wheeled drive. Though the wheels provide the vehicle with some significant advantages in range and maximum speed, these were not judged to be worth the sacrifices undertaken in ease of production, maintenance, and cross-country mobility. Source: Bronya Rossii (Russia’s Armor) Episode 8

Likely the most damning point of the wheels over the fate of the Object 911, however, was their impact on cross-country capacities. As stated previously, the wheels of the Object 911, even when retracted to their fullest extent, would not entirely be contained within the hull and would still stick out of the bottom by several centimeters. In practice, this was found to be a major issue when driving on uneven dirt roads or terrain. The wheels could occasionally touch the ground and get caught on it. The result would be that the track would lose tension and the vehicle would prove unable to negotiate the obstacle. Considering the requirements requested for a highly mobile vehicle that could move through all terrains, this was a major issue.

Another issue that likely arose by this point was the crew configuration. When compared to the favorite, the Object 765, which would eventually be chosen, the placement of dismounts to the center and front of the vehicle would prove unfavorable. While, at first, this had been the preferred solution due to the ability of the dismounts to engage with small arms towards the front of the vehicle, in practice, the rear dismounts compartment of the Object 765 allowed for a far easier and safer exit of the vehicle through dual rear doors. In this configuration, the dismounts would not have to exit from the top of the vehicle, which could be incredibly dangerous when under fire. The buoyancy of the Object 911 was also found to be overall lacking, with the vehicle being fairly unstable in water.

Conclusion – An Original Solution, Quickly Ditched

In practice, it appears the Object 911 was one of the first vehicles to no longer be considered for adoption, alongside the other vehicle which used a mixed tracks and wheels drive, the Object 19. One can fairly easily identify the reason behind the rejection of these vehicles. The dual drive would result in increasing complexity in a vehicle which would typically perform worse than a wheeled vehicle in areas generally favorable to wheeled vehicles, and worse than tracked vehicles in areas generally favorable to tracked vehicles.

A modern view of the Object 911 at Kubinka. Image provided by Pavel Alexe.

Despite this rejection, the Volgograd Tractor Plant was not entirely out of the field of infantry fighting development, largely due to the parallel development of the more conventional Object 914. In comparison to the Object 911, the more standard Object 914 had more satisfying results and appeared to have been seriously considered for longer, though, eventually, the vehicle picked would be the more novel Object 765. Volgograd Tractor Plant would still obtain a notable success in the following years in the form of the Object 915, a small and light infantry fighting vehicle which was adopted as the airborne BMD-1.

As for the Object 911, it was not, for the time, an evolutionary dead-end, as alongside the infantry fighting vehicle, a light tank would be designed using the same chassis. This would be the very low Object 911B, which appears to have ditched the wheels drive entirely and featured a small two-man crew entirely present in the turret. As with the Object 911, it would also not be adopted for service. The Object 911 has been preserved in the Kubinka Armor Museum up to this day.

Object 911 on tracks. Illustration by Pavel “Carpaticus” Alexe
Object 911 on wheels. Illustration by Pavel “Carpaticus” Alexe

Object 911 specifications

Dimensions (L-W-H) 6.735 x 2.940 x 2.040 m (maximum ground clearance)
Ground clearance 96 to 456 mm (adjustable)
Combat weight 12.07 tonnes
Engine UTD-20 6-cylinders 300 hp diesel engine
Suspension Adjustable pneumatic springs
Transmission mount rear
Forward gears 5
Road wheels (tracks) 5 per side
Wheels configuration 4×2
Wheels diameter 840 mm
Steering wheels Front
Maximum speed (road) 57 km/h on tracks, 108 km/h on wheels
Cruise speed (road) 70 km/h on wheels
Maximum speed (water) 10.3 km/h
Range 350-500 km (dirt roads, tracked drive)
Up to 1,350 km (highways, wheeled drive)
Crew 2 (driver, commander/gunner)
Dismounts 8
Main gun 73 mm 2A28 ‘Grom’ with 40 rounds
Autoloader Electrically-driven horizontal conveyor belt
Secondary armament Coaxial 7.62 mm PKT with 2,000 rounds
Missile armament 9M14 Malyutka ATGM with at least 2 missiles, possibly more
Effective armor protection Heavy machine gun fire (frontal arc), rifle-caliber projectiles and artillery shells splinters (sides and rear)
Numbers produced 1

Sources

Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
73-мм ГЛАДКОСТВОЛЬНОЕ ОРУДИЕ 2A28 Техническое описание и инструкция по эксплуатации (73-mm SMOOTHBORE WEAPON 2A28 Technical description and operating instructions)
БОЕВАЯ МАШИНА ПЕХОТЫ БМП-1 ТЕхничЕскоЕ ОПИсаниЕ И ИНСТРУКЦИЯ ПО ЭКСПЛУАТАЦИИ (COMBAT VEHICLE INFANTRY BMP-1 Technical Description AND THE OPERATING INSTRUCTIONS)
Bronya Rossii (Russia’s Armor) Episode 8
BMP-1 field disassembly, Tankograd
skylancer7441’s archive
Kubinka tank museum website

With special thanks to Alex Tarasov and Pavel Alexe for their help in researching and writing this article

Categories
Cold War Soviet Prototypes

7.5 cm SPG (Soviet Hetzer Starr)

USSR (1945-1946)
Self-propelled gun – Partial blueprints only

Bridging the seemingly non-existing gap between fiction and reality are the post-war Soviet experiments on the German Hetzer Starr technology. The German use of a rigidly mounted gun in an AFV, without any recoil absorption systems, interested the Soviets so much that German engineers that worked on the project were brought in. Studies were made, with blueprints of an AFV hull nearly identical to that of the German Jagdpanzer 38(t) Starr. To what extent these studies went, and if a vehicle was truly intended for testing, is unknown.

Origins

The German Jagdpanzer 38(t), usually referred to and more famously known as the ‘Hetzer’, has become an icon of the latter part of the German armored fighting vehicle arsenal during the Second World War. Its combat record and value impressed many, so much so that production continued post-war in Czechoslovakia as the G-13. It used well sloped armor on all sides, allowing for good protection despite the thin armor plates. The 7.5 cm Panzerjägerkanone 39 L/48 proved to be well suited for a variety of duties.

Truth is that the concept was not entirely new. The Romanians had experimented with the concept of angled walls prior to the Jagdpanzer 38(t), in their Mareşal program. On the other hand, the Soviets began as early as 1940 to work on a very cheap, light self-propelled gun which would use angled plates for better protection. Throughout the war, many variants were drawn up, built and tested, but none ever saw service. They usually tend to be simply called Russian Hetzer(s), a post war designation probably originating from Russian author Mikhail Svirin.

The last of these projects began in late 1945 and sought to offer the Soviet army an extremely cheap vehicle. It used the widely available parts from various obsolete vehicles, of which thousands were leftover after the war effort. The project was inspired from the Hetzer Starr variant, a late war production variant of which less than 20 were built. For this, German designers were brought in.

Hetzer Starr out of the December 1944 – April 1945 production batch at Skoda factory.Source: Topwar.ru

Jagdpanzer 38(t) Starr

The Jagdpanzer 38t Starr, the basis for the Soviet project, began life almost as soon as the first production versions rolled out. The word ‘starr’ is German for rigid or reinforced. The main theory behind it was to simplify production and lower the weight. Two critical points were explored, namely attaching the gun mount to the hull floor instead of the front plate roof and removing the recoil systems. Other features of the upgrade included replacing the infamous saukopf (English: pigs snout) mantlet with a more angled, bullet-shaped one, and the replacement of the engine, which in turn required a new engine deck and exhaust system.

Changing the gun mount would lower the overall weight of the vehicle, and improve production cost and speed. Another advantage of the system was more internal space for the crew, thanks to the removal of recoil equipment. Both Alkett and Rheinmetall-Borsig had made various gun mounts and trials on the idea, with several outcomes, including a 10.5 cm gun mount.

Yet the entire project proved problematic throughout the development process, as the high recoil shock and stress created gaps, cracks and loosening in the different gun and hull components. These issues were more or less fixed by the end of the war, but how reliable this technology would be in an active fighting vehicle remained an unanswered question.

A production batch of 10 vehicles was ordered in December 1944 and ended in April 1945. Yet only 2 of these vehicles left the Milovice training center.

The gun mount of the Jagdpanzer 38(t) Starr. Note how it is mounted to the hull floor and the new, more streamlined gun barrel.Source: Panzerfahrer

Development

After the end of the Second World War, the Soviets were able to capture and analyze the Starr, and were impressed by its use of a fixed mount for the gun. Thus, in November 1945, German engineers that worked on the Starr project were brought to the USSR to continue the project for the Soviet military. Studies continued into summer of 1946. As per Russian author Mikhail Svirin, one study was made for the production of a Soviet variant, more or less identical to the original German AFV. The project was commissioned by M.N. Shukin, chief designer at OKB-38.

Previous light Soviet tank destroyer projects were made at the Gorkovsky automobile plant (today known as Nizhny Novgorod), with some ‘Hetzer like’ projects as early as 1942. Work continued throughout the war, with the most advanced being the GAZ-75, also named the SU-85 (not to be confused with the T-34 based SU-85), an 18-tonne tank with 82 mm of frontal armor and an 85 mm D-5S-85 gun. It was designed in just 26 days, with I.V. Gavlov as lead designer. Despite the promising work head engineer of the GAZ factory, A. A. Lipgard canceled all AFV developments at his factory. This was not done as an act of sabotage, but rather because he wanted to prepare the factory for peacetime, when an automobile plant would not need to build tanks. By March 1944, the GAZ-75 (SU-85) was dead.

The GAZ-75 (SU-85), the apex of wartime Soviet light tank destroyers. It was armed with a 85 mm gun and 82 mm of frontal armor. Source: Yandex.ru, colorized by Smaragd123

After the great efforts of the Great Patriotic War, the Soviets found themselves with a large amount of equipment from obsolete light tanks, such as the T-30, T-40, T-60, T-70, and T-80. In a letter from the 10th of April, 1945, Deputy Commander of the Armored and Mechanized Forces, Colonel General of the Tank Forces Korobkov stated:

These vehicles are obsolete, as they have weak armament and insufficient armor. They cannot be used in battle and are only used in training units.
It would take a considerable expense to restore these tanks. Repair units are loaded with repairs of modern tanks, and it is not reasonable to distract them with repairs of obsolete vehicles.
I ask for your permission to use the aforementioned tanks until they require refurbishment, after which they will be written off and disassembled for parts. These parts will be used for light and medium repairs of tanks that are still being used.
These parts proved to be useful for many post-war AFV developments, with certain factories, like OKB IC SV in Moscow, were notorious for using components from these obsolete light tanks. Thus, there is no surprise that, when developing a light and very cheap light self-propelled gun, their components were to be used.

Where exactly the German-Soviet Hetzer Starr design was made is unknown. Equally uncertain is how far the project went. It could have simply been a technology transfer to simply test the viability of a rigidly mounted gun in an AFV. Or, as M. Svirin suggests, it went as far as an SPG designed for the Soviet army. There is not much to back this claim up other than a set of blueprints which lack any sort of automotive components.

Design

Soviet-German efforts largely reproduced the ‘Hetzer Starr’. Drawings of the hull of the project and its gun are almost identical to those of the original German blueprints. Yet some design elements were changed, for example having a single armored side plate instead of two. The drawings do not give a name to the project, and are simply labeled as 7.5 cm KwK self-propelled gun, signed by Captain Dernov. The point was to create a simple and cheap vehicle, in part to replace obsolete light tanks and SPGs. The gun was mounted to the floor of the tank, and able to pivot towards the sides an unknown amount. The crew consisted of 4 men, a commander, gunner, loader, and driver. The crew compartment and the engine were separated by a firewall. Ammunition was probably stowed along the angled side walls.

The studies made by the German and Soviet Engineers. Note that they are almost identical to the Jagdpanzer 38(t), with some exceptions, such as the single side armor plate.Source: M. Svirin via Topwar

The armament was of German origin, likely a 7.5 cm PaK 39/1 (L/48). Even the roof periscope was a typical German design, firmly attached to the gun and traversing via a cutout in the roof, covered by an armored plate. The system had a gun elevation of 15° and -8° of depression.

7.5cm Panzerjägerkanone 39 L/48 anti-tank gun armor penetration

(The data was obtained on a firing range. The armor plate was laid back at a 30-degree angle)
Pzgr.Patr. 39 Pzgr.Patr. 40 Gr. Patr. 38 HL
Shell Weight 6.8 kg 4.1 kg 5 kg
Initial velocity 750 m/s 930 m/s 450 m/s
Range
100 m 106 mm 143 mm 100 mm
500 m 96 mm 120 mm 100 mm
1000 m 85 mm 97 mm 100 mm
1500 m 74 mm 77 mm 100 mm
2000 m 64 mm 100 mm
(Source: Spielberger, Jentz and Doyle)

Armor would have been the same as on the German Jagdpanzer 38(t), with 60 mm at the front, sloped at 30°. The side and rear armor was 20 mm.

German drawings showing the armor thickness and angles of the Jagdpanzer 38(t).Source: User Wotichen via WT Forums

Components not drawn in were likely meant to be of Soviet origin, tying in with the aforementioned obsolete light tanks and GAZ experience with designing such light tanks. Propulsion could have been dual GAZ-202 70 hp engines, for a total of 140 hp, or dual GAZ-80 85 hp engines. Considering the similarities with the German Hetzer Starr, the total weight would have been between 15 and 16 tonnes. A hypothetical speed of 40 km/h could have been reached. No details are yet available on the running gear. If already available components were to be used, then 5 to 6 wheels sprung by torsion bars seem logical.

Conclusion

The Soviet experiments on the Hetzer Starr disappeared as fast as they appeared. M. Svirin claims the possibility that progress on a working prototype might have started, but that is highly unlikely. As a matter of fact, the entire project was just an experiment of testing fixed-mounted guns, as a new budget SPG based on WWII equipment was redundant and had no place in the rebuilding Soviet army. A German 75 mm gun had no place in the Soviet army, let alone after the war was already over, clearly not capable of dealing with new Western tanks. The problems of recoil damage to the hull and gun mounts were not yet fixed. The last nail in the coffin came with the development of new and more powerful recoilless guns. While harder to implement in an enclosed AFV, the whole concept was more fruitful than the rigidly mounted gun.

Soviet copy of the German Hetzer Starr. Illustration by Pavel Alexe.
Soviet Hetzer Starr Specifications
Dimensions (approx) (L-W-H) 3.70 – 2.63 – 2.10 m
Total weight, battle-ready 15-16 tonnes
Crew 4 (Commander, Gunner, Driver & Loader)
Propulsion 2x GAZ-202 70 hp enginesOr2x GAZ-80 85 hp engines
Speed 40 km/h (hypothetical)
Suspension Torsion bar, 5 to 6 wheels per side
Armament 7.5 cm Pak 39 L/48
Armor Armor: 60 mm angled at 30 deg.20 mm side and rear
No. Built 0, partial blueprints only

Sources:

Stalin’s self-propelled guns M. Svirin
Soviet Hetzers – M. Svirin via Soviet Hetzers (topwar.ru)
The theory of armored errors: the middle of the Great Patriotic | Warspot.ru – Yuri Pasholok
Лёгкие САУ с большими пушками | Warspot.ru – Yuri Pasholok
http://www.pzfahrer.net/starr.html
Tank Archives: Obsolete Tanks – Peter Samsonov
Tank Archives: Soviet Light Tank Destoyers – Peter Samsonov
Tank Archives: An Alternative from Gorky – Peter Samsonov

Categories
Cold War Soviet Prototypes

Object 705A

USSR (1945-1948)
Super heavy tank – Blueprints only

Megalophilia is a term rarely encountered in the world of military history, yet the phenomenon has been a recurring theme since the beginning of mankind (and, ultimately, wars). Massive weapons of war, envisioned to destroy and conquer any enemy resistance, more often than not failed hilariously, hurting their creators more than the enemy. In popular history, Nazi Germany is the one most often mentioned in regards to this topic. One does not even have to mention the Maus tank, Schwerer Gustav railway gun, Bismarck battleship or the Me 323 Gigant transport aircraft.

The fascination for super-heavy tanks was a common theme prior to the Second World War in several nations and continued into the war. The Soviets had their own fair share of such heresies, such as the Edward Grote’s designs, T-42, KV-4, and KV-5 and more. However, the theme of such heavy tanks slowly died during the war, with the occasional exception. One such exception was the Object 705A – a 100-tonne super-heavy tank armed with a 152 mm gun and having dozens of centimeters of raw armor, as Soviet tank design moved towards more advanced protection philosophies, such as low silhouettes and steeply angled plates requiring thinner armor.

Yet, with the discovery of the German monster tanks, like the Maus and Jagdtiger, Soviet officials realized that their own heavy tanks were inferior. Although the war was over, further developments on even heavier tanks continued. On the 11th of June, 1945, the GABTU ordered the development of a 60-tonne heavy tank armed with a S-26 130 mm gun and the suspension had to be torsion bars. Kirov Chelyabinsk (ChKZ) answer to this request came in the form of the Object 705 and Object 705A, while Kirov Leningrad (LKZ) came in the form of the Object 258, Object 259 and Object 260 (IS-7).

Ironically, on the 2nd of April, 1946, not even a year after the initial request, V.A. Malyshev ordered all heavy tank projects above 65 tonnes to be canceled. However, his request did not hold up in practice, with the 100 tonne Object 705A still being under development and the ultimate versions of the IS-7 weighing over this threshold.

One of the final IS-7 prototypes. While certainly a massive tank, and likely on par with the Object 705A in terms of dimensions, the 100-tonne weight of the Object 705A makes them hard to compare.
Source: Soldat.pro

Design

The Object 705A was a direct evolution from the Object 705, a lighter 65-tonne heavy tank. Both vehicles featured a rear-mounted turret for better balancing of weight and to reduce gun overhang. The Object 705A was to be armed with a colossal 152 mm M-51 gun, using two-part ammunition and two loaders. Weighing 100 tonnes on paper (a figure likely to grow as the design would transition from paper to reality), the armor would have been impressive in raw thickness, yet clever use of angling the side armor plates into a diamond-like shape, the overside protection was increased. To protect itself from infantry, soft-skin vehicles, and even aircraft, a secondary turret was added to the rear of the turret, armed with 2 KPVT 14.5 mm heavy machine guns.

It likely had a crew of 5; commander, gunner, 2 loaders and driver, in a standard Soviet crew layout. The driver sat alone in the hull, while the massive turret encompassed the rest of the four crewmen.

Silhouette of the Object 705. The Object 705A would have likely been similar in layout, just larger.
Source: TiV No. 09 2013

Hull

The exact details of the tank remain mostly unknown. Even a full blueprint of the hull is, so far, missing. Careful analysis and speculation would indicate that the hull was very similar to that of the ‘lighter’ Object 705, but lengthened to fit the larger turret and heftier rounds. The Object 705A would have been 35 tonnes heavier, out of which at least 10 tonnes would come from the larger turret and the 152 mm gun and its ammunition. The remaining 25 tonnes would likely come from thicker frontal armor, overall increased hull volume, and a new engine. This new engine would have had a power output of 1,000 and 1,500 hp, to be able to reach useful speeds. The transmission was a planetary system automatic. In terms of suspension, a single torsion bar per wheel was used.

One of the main reasons behind the Object 705A was for more armor. Although the exact armor values are yet unknown, comparison to the Object 705 and other heavy tanks of the time (also taking in consideration the weight) results in the frontal hull being at least 220 mm thick, angled at circa 60 degrees. The side armor would be at least 150 mm thick angled inwards at circa 57°. The rear armor angled upwards and was at least 120 mm thick.

152 mm M-51

One of the few certain things about the Object 705A is the main armament, the M-51 152 mm gun, developed at Factory No.172 as a tank variant for the 152 mm M-31. In terms of ballistics, it was mostly identical to the regular M1935 Br-2 howitzer, but with considerable upgrades in other areas. Firstly, the archaic breech block door was replaced with a more modern horizontal sliding breech block. It also received the famous TsAKB style slotted muzzle brake, which could absorb up to 70% of the recoil, decreasing the need for powerful recoil absorption pistons. It still had two recoil absorption cylinders and two brake cylinders to absorb recoil, but these were considerably lighter, and in tandem with the muzzle brake, decreased the recoil from 1,400 mm (on Br-2) to 520 mm. Very noticeable is the sheer volume of the breech, which was needed to offset the long barrel. One prototype of the gun was built and passed factory tests in the summer of 1948.

Soviet slotted muzzle brake compared to a German-style muzzle brake.
Source: Tank – The Military Publishing House of the Ministry of Defense of the USSR

Turret

The only known blueprint is of the turret, a lengthened variant of the original. It almost resembles a UFO-like shape to increase the angle at which most projectiles would hit the surface. To cut down on the weight, the rear and top has been limited to around between 30 and 50 mm of armor, while the front has over 250 mm thick. The mounting of the M-51 gun is also very clear, showing the lack of gun depression. It is also significantly longer than the original to compensate for the larger recoil and potentially even turret-stowed projectiles.

On the roof of the turret, the turret ring of a second, smaller turret can be seen. This was a brand new design feature incorporated on some heavy ChKZ designs, first incorporated on the Object 726, and apparently, also the Object 705A (as the two were likely designed simultaneously). The turret resembles contemporary American tank secondary turrets, having a hemispherical shape. It was armed with a pair of 14.7 mm KPVT heavy machine guns. It was far too small for a crew member to fit in it, and was probably mechanically controlled from within the turret by one of the loaders. The idea was not entirely dropped after the cancellation of these super-heavy tanks. The Object 777 still used a similar turret, but with only one turret KPVT. For the turret traverse, ChKZ created hydraulic drives in 1948, but they were deemed unsuccessful and shortly after, the entire project was canceled.

Cutout view of the turret showing its armor thickness and the M-51152 mm gun.
Source:TiV No. 09 2013
The Object 726 model 1947, designed in parallel with the Object 705A, but weighing less than half of it, at just 48 tonnes.
Source: TiV No.10 2014
The 4-tracked Object 726 mod. 1948. The second turret on top was likely very similar to that of the Object 705A.
Source: TiV No.10 2014

Suspension & Running Gear

As this would be amongst one of the heaviest tanks ever designed by SKB-2, seriously strong suspension and running gear were needed. An entirely new set of large-diameter wheels was designed for the program. The Object 705 likely used the same wheels.

As per the blueprints, the wheels were steel-rimmed, clamped between two stamped steel lids. This left a distinctive space between the rim and the interior of the wheel. The same wheel system is mirrored on the other side. The two parts are held together with large bolts, creating a space for the track guides.

The suspension consisted of relatively simple torsion bars, running from the wheel straight into the narrow hull. The torsion arms were mounted in opposite facing pairs, instead of facing the same direction, like on other torsion bar sprung tanks. The spacing in-between each torsion bar pair was enough to fit another torsion bar, as seen in the blueprints.

Side cutout view of the wheels used on the Object 705A. These were likely designed specifically for the project.
Source: TiV No. 09 2013
Side cutout view of the torsion arm and torsion bar attachment on the Object 705A. Note the steep angle of the hull.
Source: TiV No. 09 2013
Cutout top view (left) and cutout side view (right) of the torsion bar arrangement. Note how they are mounted in opposite facing pairs, an unusual solution.
Source: TiV No. 09 2013

A Maturing Tank Force

Although being under development for almost 3 years (a very long time for Soviet standards), the Object 705A never got particularly far. Both the GABTU and Soviet officials began discouraging especially heavy tank projects. Even internally, ChKZ was focusing on other, more fruitful projects, like the IS-3 and IS-4 or various self-propelled guns.

It also started to become clear that heavy tanks were beginning to get outperformed by medium tanks. Development of the T-54 had reached an advanced stage in the late 1940s, with better mobility and lower weight, yet the firepower and armor were not far behind.

In contrast, heavy tanks, especially super heavy ones, like the Object 705A, would hinder the Soviet tank force rather than improving it. Such a heavy tank, not only requiring massive amounts of money and resources poured into developing, production and maintenance, would also require an entirely new logistical force, from rail cars to mobile bridges.

Ultimately, the Object 705A, alongside its lighter brother the Object 705 and its LKZ rival, the IS-7, all got their lives cut short by the Council of Ministers of the USSR on the 18th of February, 1949, where it was requested that the development of all heavy tanks and SPGs weighing over 50 tonnes should be terminated.

The Soviet Union would ‘force itself’ into adopting a new heavy tank into service, despite the rather large disappointments in the form of IS-3 and IS-4. This would be the T-10, one of most modern heavy tanks of the time. Whether or not it was necessary is up for debate. The British Conqueror heavy gun tank and American M103 heavy tank entered service in the mid to late 1950s.

Soviet heavy tank development continued into the 1950s, with very advanced designs, such as the Object 279 and Object 770, far ahead of any contemporary Western heavy tank. They were, however, redundant as by now, new Soviet medium tanks could easily outperform any heavy tank using new technologies. On 22nd July 1960, Nikita Kruschev forbade the development and adoption into service of all tanks weighing over 37 tonnes. Thus, all heavy tank development stopped.

A hypothetical look of the Object 705A. Illustration by Pavel Alexe.

Object 705A Specifications

Dimensions (L-W-H) 7.2 – 3.7 – 2.4 m
Total Weight, Battle Ready 100 tonnes
Crew 5 (Commander, Gunner, Driver & 2 Loaders)
Propulsion 1000+ hp engine of unknown type
Speed 35 km/h (hypothetical)
Range Torsion bar, 7 wheels per side
Armament 152 mm M-51 gun
coaxial 14.5 mm KPVT heavy machine gun
Secondary turret w/ dual 14.5 KPVT
Armor Hull armor:
Approx.
Front top plate: 220 mm at 55°
Front bottom plate: 200 mm at -50°
Side plates: 150 mm at 57° (inwards)
Rear plates: 120 mm
Top: 30 mm
Belly: 30 mm
Total Production 0, blueprints only

Sources

Domestic armored vehicles 1945-1965 Soljankin, A.G., Pavlov, M.V., Pavlov, I.V., Zheltov
TiV No.10 2014 A.G., Pavlov, M.V., Pavlov
TiV No. 09 2013 A.G., Pavlov, M.V., Pavlov
https://yuripasholok.livejournal.com/2403336.html
The genius of Soviet artillery. Triumph and tragedy of V. Grabin – Shirokorad Alexander Borisovich

Categories
Cold War Soviet Prototypes

Object 705 (Tank-705)

USSR (1945 – 1948)
Heavy tank – None built

Background

In the latter stages of the Second World War, a great deal of Soviet tank design focused on improving existing heavy tanks, such as the IS-2, and building entirely new designs. This resulted in a number designs, with various degrees of performance and success, such as the IS-6 and IS-3.

After the discovery of the Maus and an in-depth look at German projects, the Soviets thought that the new imminent war against the West would require serious heavy tanks, with more armor and better guns than what they currently had. So, on 11th June, 1945, the GABTU (Main Directorate of Armored Forces) requested the development of new heavy tanks armed with the 130 mm S-26 gun, weighing 60 tonnes, and using torsion bar suspension. This led to a series of complex heavy tank and SPG designs, which would eventually lead to the heaviest Soviet tank of all time – the IS-7.

Developed and built at Kirov plant Leningrad after almost 5 years of development, the IS-7 is often regarded as the peak of heavy tank design. However, the Soviets officials’ displeasure with such heavy vehicles led to the cancellation of design and development of all AFVs weighing over 50 tonnes. The act came into practice at the meeting of Ministers of the Soviet Union on 18th February 1949, ending the IS-7’s life.

But few know of the other Kirov plant’s design, meant as a rival to the IS-7 (Object 260). Kirov Chelyabinsk (ChKZ) and Kirov Leningrad (LKZ) had been rivals for years, and so there are many parallel projects by the two factories. Their design was called Tank-705 as per the blueprints, but would eventually be known as the Object 705. The project started in June 1945 and was terminated in 1948, alongside other heavy tanks.

Development first began in June 1945, immediately after the discovery and analysis of German heavy AFVs. This triggered a series of projects over several design bureaus and factories. For ChKZ, the IS-3 was proving to be a success, and the IS-4 (Object 701) was soon to enter production. In contrast, LKZ had just lost several programs, most importantly, the IS-6. But the experience gained from it led to a series of promising designs. Fast forward a couple of years, and LKZ had full-scale mock-ups of one of the best heavy tanks ever designed, and was beginning prototype production. Meanwhile, Chelyabinsk and its design institute, SKB-2, had a series of disappointments, especially in the IS-4. In parallel, ChKZ had been working on the Object 705 and 705A designs, but, as they were not deemed crucial or urgent, progress was slow. Further problems came with the 80th order on 2nd April, 1946 from V.A. Malyshev, when the mass of heavy tanks was limited to 65 tonnes. While the Object 705 still fit the criteria, the Object 705A did not. Yet work continued regardless.

The 1946 LKZ Object 260 was very similar to the Object 705 in terms of capabilities, although it came slightly later.
Source: Domestic armored vehicles 1945-1965

Design

All that remains of the Object 705 are two drawings, one general silhouette and one detailing the armor profile and thickness. The tank was meant to weigh around 65 tonnes, use heavily sloped armor plates, and mount a thick cast turret mounted to the rear. This was done not only to use the engine as protection, but to also offset the length of the gun. What exact engine it would have used is unknown, but likely one between 750 and 1,000 hp for it to reach the expected 40 km/h. The transmission was a planetary automatic design. It is important to highlight is the sheer size of the tank design, being 3.6 m wide and 7.1 m long (just the hull), dwarfing the IS-4 (6,682 (hull only) x 3.26 x 2.4 m).

Dark silhouette view of the Object 705 with the dimensions. This is the only known drawing showing the complete view of the vehicle.
Source: TiV No.9 2013

The crew was probably of 4: commander, gunner, loader, and driver. The crew were all situated inside the turret, with the gunner on the left side of the gun, the loader behind, and the commander on the opposite side. The driver was placed inside the turret, and would have a pivoting station, which allowed to always face the front of the hull. This was not the first, nor last, time Soviet designers would try to incorporate this idea. Two of the periscopes were mounted on the turret roof, the one on the left side was to be used by the commander and the one on the right was to be used by the loader. The driver also had his own periscope, but mounted further forwards. The gunner likely did not have his own periscope, and had to rely on his sight and/or crew callouts.

Armament

In terms of main armament, it is uncertain what the Object 705 would have used. Some sources claim it was a high-power 122 mm gun, while others state directly that it was a BL-13 122 mm gun. This was no new and revolutionary gun by the late 1940s, it was actually developed by OKB-172 in 1944, with several upgrades made later, such as the BL-13T and BL-13-1. The rate of fire varied between the different versions of the gun, as the upgraded variants had a mechanical gun rammer, but it was between 5 to 10 rounds per minute. Such long reload times were caused by the two-part ammunition. Secondary armament consisted of a coaxial 12.7 mm DhSK heavy machine gun mounted on the right side of the gun and potentially a roof-mounted DhSK.

However, a larger caliber gun (130 mm) is not entirely out of the equation, as later IS-7 designs used such a caliber, and the diameter of the barrel on the silhouette of the tank is thicker than that of a 122 mm gun. To back this theory up, on 11th June, 1945, specifications clearly stated that the gun on the new heavy tank should be a 130 mm S-26, the land version of the naval B-13. At the same time, the BL-13 was already deemed obsolete when facing German heavy tanks.

The S-26 was developed between 1944 and 1945 at TsAKB by head engineer V.G. Grabin. It was largely based on the B-13 130 mm naval gun (not to be confused with the previously discussed BL-13) with a semi-automatic horizontal sliding breech lock, slotted muzzle-brake, and barrel smoke evacuator. Rate of fire was around 6 to 8 rounds per minute. The shells weighed 33,4 kg and had a muzzle velocity of 900 m/s.

Ammunition was stored along the angled sidewalls, a solution present on most Soviet tanks with angled sidewalls. The exact number of rounds stowed is hard to estimate, but most tanks using similar guns carried around 30, split into charges and projectiles.

Digitally blue-tinted drawings of the BL-13 122 mm gun. Note that the barrel length proportions are not to scale.
Source: Warspot
S-26 130 mm gun. This was the gun GABTU requested to be mounted on the heavy tank in the summer of 1945.
Source: Domestic armored vehicles 1945-1965 Soljankin, A.G., Pavlov, M.V., Pavlov, I.V., Zheltov

Armor

A study of the drawing showcases the armor thickness and the complex arrangement of the armor plates. The upper frontal plate consists of one 140 mm thick plate, angled at 60°. On the top corners, it is met by a plate angled upwards across the upper side of the engine bay. The lower plate is also 140 mm, angled 55º from the y-axis. In terms of side armor, a very interesting idea was adopted. The two 130 mm armored side walls were brought inwards at a steep 57° angle, creating a diamond-like shape from the front. SKB-2 had used angled walls on the IS-3, but only on a minimal level for more interior space. Instead, such diamond-shaped sides were first used by the Kirov Leningrad plant on the first IS-7 design, the Object 257. This option provided excellent side protection from conventional projectiles, but also increased mine resistance, as the blast force was directed outwards. All this came as a trade-off for interior space. A major issue with this design feature is the narrow-angle created at the bottom of the tank. This space is very hard to use, and essential components like engine and transmission have to be moved up, making the tank taller. Another big issue was the suspension, namely where exactly to put it. On the Object 257, the issue was resolved by designing a brand new external suspension, using volute spring bogies like on the Sherman tank. The exact solution on the Object 705 is, naturally, unknown, but a handful of different options could have been used.

The turret was rounded and flat, creating angles between 50º and 57º. Armor varied greatly depending on the strike face, with the thickest front part being 140 mm and the thinnest roof section being 20 mm.

Cutout armor profile of the Object 705. Note the protrusions from the hull for the final drive.
Source: TiV No.9 2013

Roadwheels and Suspension

One of the most curious aspects of the design was its wheels. Seven large steel-rimmed wheels per side were used. A hint comes from SKB-2’s other super heavy tank project at the time, the massive 4-tracked Object 726 behemoth, which featured among other wheel and suspension ideas, large, steel rimmed roadwheels. There is a serious possibility of them being used on the Object 705 as well. These wheels would later become a mainstay in heavier ChKZ designs, such as the Objects 752, 757, 770, and 777, the latter two using hydropneumatic suspensions.

Steel-rimmed roadwheel from the Object 770 at Kubinka.
Source: Magic Models

Yet blueprints of the Object 705A show a slightly different set of wheels. These were drawn as steel rimmed and with deep spacing between the rims and rest of the stapled steel lids. The wheels seem to have been mostly unique to the Object 705A. The Object 705 could have used the same wheel design or something else, as the lower weight allowed for more playroom in terms of weight thresholds on the components.

Cutout view of the roadwheel used on the Object 705A. These were different to other large-diameter wheels used by ChKZ.
Source: TiV No.9 2013

Implementing conventional torsion bars running across the length of the hull initially seems challenging due to the hull floor being so narrow, due to the inwards angled side walls. Yet the simple solution to this was that the tank hull was simply very wide. This allowed the side walls to keep a steep angle while still allowing for a sufficiently long torsion bar to be mounted. Such issues had been encountered by Soviet engineers both previously and later, with a variety of solutions such as bundled torsion bars, lifting the torsion bars higher up into the hull, or moving the torsion arm on the outside of the wheel.

Cutout view of the suspension (single torsion bar) used on the Object 705A. Note the angle of the hull.
Source: TiV No.9 2013

Object 705A

At some point during the development of the Object 705, an even heavier variant was designed. It would have weighed 100 tonnes and be armed with the 152 mm M-51. Just the mass alone would place the Object 705A as one of the heaviest Soviet tanks designed post-war. Yet blueprints only show specific details, such as the turret, suspension, roadwheels, and transmission. A lack of hull blueprint makes it hard to legitimize it as a complete design, and it is entirely possible that its hull never got drawn to begin with. This naturally leaves the proposal in a lot of mystery and up to significant speculation.

Conclusion – Weight Shaming

With so little information available, it is hard to properly judge the capabilities of the Object 705 and 705A, even when compared to the different variations of the IS-7. The vehicles were likely designed between 1947 and 1948, at which point the BL-13 was already outclassed (Kirov Leningrad had used it on the IS-6 and other projects in 1945). So, in that respect, the Object 705 fell behind the IS-7. Yet in terms of armor, it was on par, if not even better protected than the most advanced IS-7 variant. As for the Object 705A, the lack of information prevents any conclusions to be drawn, with the one and main issue being the weight of 100 tonnes. When discussing both the Object 260s and Object 705s, it is generally clear that such heavy vehicles could prove vulnerable and simply too heavy for effective battlefield use. The heaviest Soviet tank in service, the IS-4, weighed 53 tonnes and was still considered overweight and too slow. Thus it seems almost natural that the Soviet government saw the limitations and waste of resources devoted to such heavy vehicles. The final nail in the coffin for these designs was the cancellation of all AFVs above 50 tonnes on 18th February, 1949.

Object 705 rendition, illustrated by Pavel ‘Carpaticus’ Alexe

Object 705 specifications

Dimensions (L-W-H) 7.1 – 3.6 – 2.4 m
Total Weight, Battle Ready 65 tonnes
Crew 4 (Commander, Gunner, Driver & Loader))
Propulsion 1,000 hp engine of unknown type
Speed 40 km/h (hypothetical)h
Armament 130 mm S-26
or
122 mm BL-13 gun
coaxial 12.7 mm DShK heavy machine gun
Armor Hull armor:
Front top plate: 140 mm at 55°
Front bottom plate: 140 mm at -50°
Side plate: 100 mm at 57°
Top: 20 mm
Belly: 20 mm
Total Production Blueprints only

Sources

Domestic armored vehicles 1945-1965 Soljankin, A.G., Pavlov, M.V., Pavlov, I.V., Zheltov
TiV No.10 2014 A.G., Pavlov, M.V., Pavlov
TiV No. 09 2013 A.G., Pavlov, M.V., Pavlov
https://yuripasholok.livejournal.com/2403336.html
The genius of Soviet artillery. Triumph and tragedy of V. Grabin – Shirokorad Alexander Borisovich

Categories
Cold War Soviet Prototypes

Object 911B

 

USSR (1963-1964)
Light tank – 1 prototype

The evolution of warfare and technologies in the years following the conclusion of the Second World War had a major impact on the way warfare would be conducted in the future. With the proliferation of nuclear armament, radiation protection became a major feature for new vehicles. Operations in the Second World War also showed that river crossing could sometimes prove difficult, as these could form major natural blocking points that most armored vehicles would find impossible to cross outside of a few heavy and sturdy bridges. Amphibious vehicles would prove to be a major asset to cross rivers even outside of these bridges, or in the event that they were destroyed or heavily defended. Many amphibious light tank designs were created in the late 1940s to early 1960s. The Soviet design bureau of the Stalingrad/Volgograd tractor plant was behind several of them. The most famous is without a doubt Object 740, which became the PT-76, the most produced light tank of the Cold War. In the early 1960s, Volgograd would design a prototype infantry fighting vehicle for the program which would lead to the BMP-1. A light tank prototype would also soon follow using the chassis and suspension of this infantry fighting vehicle. The infantry fighting vehicle prototype was designated Object 911, and, as such, the light tank would be Object 911B. Both included some innovative or original features, but none would be adopted by the Soviet military.

A photo of Object 911B during its trials, with the suspension set for higher ground clearance. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

Volgograd’s Object 911 and 906

The idea of a combat vehicle that would combine amphibious capacities, a dismounted infantry complement, and an armament that could provide fire-support to these infantry dismounts and accompanying tanks was developed in the late 1950s Soviet Army. A formal call for prototypes fulfilling this role to be designed was issued by the GBTU (The General Armored Directorate, the service in charge of armored vehicles procurement) on October 22nd 1960. The requirements were sent to a large number of design bureaus, and, at that time, called for an 11-12 tonnes vehicle that would feature a crew of 2 and transport 8 to 10 infantry dismounts.

One of the manufacturers which began work on a design was the Volgograd tractor plant (VgTZ). Volgograd had extensive experience in amphibious vehicles design from the PT-76, which it had been producing since the early 1950s, and of which a number of derivative designs had already been designed.

Soviet naval infantry PT-76B moving through water in front of a Whiskey-class submarine. The PT-76 was without a doubt one of Volgograd’s greatest successes. Source: twitter

Volgograd’s proposals, by 1963, took the shape of two distincts prototypes, the Object 911 and the Object 914. The Object 914 took the clear basis of the PT-76 chassis. The Object 911, however, was more distinct. Though there was still PT-76 inspiration and a number of common parts, such as the hydrojets and road wheels, the vehicle differed massively in other aspects. Likely the most noticeable were the four large, retractable aviation wheels which could give the Object 911 a wheeled drive, intended for use on roads during transfers to increase maximum speed and reduce fuel consumption. Object 911 also used an adjustable suspension which could be used to change the ground clearance of the vehicle.

The Object 906, a vastly improved amphibious light tank design Volgograd was working on from 1960 to 1963. The general layout of its autoloader would be picked up by Object 911B. Source: pinterest

In the same timeframe as it worked on infantry fighting vehicle prototypes, Volgograd had also designed and produced three prototypes of the Object 906. This was a vastly modernized and improved design based on the PT-76. It included a new, more powerful diesel engine, as well as an autoloaded 85 mm gun which significantly improved firepower in comparison to the PT-76’s 76 mm gun, particularly against armored targets and at range.

The Object 911B

By 1963, the Object 906 was at the testing stage with three prototypes, and would eventually be rejected within the year. At the same time, work had concretized on the Object 911, and manufacturing of the prototype took place within this year.

A ¾ view of the Object 911 prototype on its tracks. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

If the Object 911 was to be adopted, it had been made clear by the GBTU’s requirements that the vehicle’s chassis was to be used for a whole family of various derivatives. This could, for example, include a light amphibious tank, something Volgograd had extensive experience with. The other Volgograd prototype from the program, the Object 914, used a more conventional drivetrain which could perhaps be easier to modify into derivatives. But, being very similar to the PT-76, there would be little reason to design a light tank version of the Object 914, seeing as the Object 914 could already be described as an infantry fighting version of a light tank. In comparison, the Object 911 could provide a more interesting base, particularly as the vehicle had an overall low profile enhanced by an adjustable height suspension.

Volgograd had already worked on a very low-profile amphibious light tank in the form of a derivative of the Object 906. This was the Object 906B, which was armed with a 125 mm tube missile launcher and featured two crewmembers in the turret. While work on the Object 906 and the Object 906B was discontinued during 1963, re-using components from them, notably the autoloader from the Object 906 and the general layout of the Object 906B, could prove valuable.

A profile schematic view of the Object 906B. The vehicle was never built, but the Object 911B would take direct inspiration from its layout and profile. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

As such, in 1963, the designing of a light tank version of the Object 911 would be carried out. The resulting vehicle would be named Object 911B. While using the chassis of the Object 911, it introduced a large variety of changes, not all directly linked to its function as a light tank. While keeping the same 73 mm Grom armament, it took inspiration from the Object 906B’s layout and the Object 906’s autoloader. A prototype of the Object 911B would be manufactured and tested in 1964.

The Object 911B’s Hull and Armor Layout

Schematics showing a general view of the Object 911B, as well as comparing its profile to the PT-76. Source: Imgur

The Object 911B was a particularly low vehicle. Its height would vary between 1,265 mm and 1,615 mm depending on the set height of the suspension. This was particularly small. At its lowest, the height of a child, and even at its highest, the height of an average to small man. This would result in increased survivability, as the vehicle would be a hard target to hit at range, though at the same time creating proper crew conditions with such a low profile could be difficult. Length was 7.1 m, and width was 2.8 m. The weight of the Object 911B when loaded with crew, fuel, and ammunition would have been 12.5 tonnes. Thanks to its fairly small dimensions and reduced weight, the Object 911B was air-transportable by the Antonov AN-12.

The Object 911B used a peculiar hull and armor layout in order to increase the survivability of the vehicle and crew. This is typically not an easy task on a light amphibious tank, which has to use light armor protection and cannot afford to have large, thick metal plates in order not to compromise buoyancy and to retain a light weight.

A side cutaway view showing the very peculiar armor layout and arrangement of the Object 911B. Source: Imgur
A front cutaway view showing the side armor protection of the crew compartment. Source: Imgur

To the front of the vehicle was what is typically described as a “cargo compartment”. This section was quite long, and did not contain any vital parts necessary for the vehicle to function. This storage space was reportedly capable of containing two men lying down, which could allow Object 911B to evacuate wounded servicemen. One can also imagine this feature may have been used to evacuate the crew of another knocked out or broken down Object 911B, seeing as the vehicle had a crew of two. The cargo compartment’s possible use to transport personnel in emergencies is further supported by the presence of two access hatches on the roof sides. When empty, the large size but low weight brought by this compartment would likely also help with the Object 911B’s buoyancy. The armor protection of this part of the vehicle can only be described as minimal. The front plate was only 10 mm thick, angled at 45° towards the back, while the roof was 6 mm thick and the floor a mere 4 mm. The sides likely had the same 10 mm thickness as the front, but without the considerable angling of the front plates

Behind this cargo compartment would be the crew compartment. The two were separated by an armored bulkhead. Being 35 mm thick, though mostly vertical with no or minimal angling, this bulkhead was actually intended to be the main frontal armor of the vehicle’s hull. An advantage of its position inside the vehicle was that it covered significantly less space, and as such, was much lighter than a similar armor layout applied to the front of the vehicle. When added to the 10 mm of the front armor and the considerable empty space of air separating it from the 35 mm bulkhead, this armor layout was actually quite considerable for a light infantry tank, and would typically protect the crew from heavy machine-gun fire, and often even autocannons. The front armor of the turret, which would not benefit from the 10 mm of armor of the cargo compartment and spacing separating it from the bulkhead received 40 mm of armor angled backward at 48° frontally, and 40 mm angled backward at 30° on the sides, with the same thickness to the rear. The hull sides were also quite thickly armored, with 45 mm on the upper sides and 20mm on the lower sides. The roof and floor of the crew compartment were also thicker, at 10 mm each. The crew compartment, within the vehicle’s turret, contained the two crewmembers, a driver to the right and a commander/gunner to the left.

The crew compartment was then separated from the rear compartment by another 35 mm bulkhead. The vehicle’s powerplant and transmission were to the rear. This part of the vehicle had the same light armor layout found on the front cargo compartment. The floor was 4 mm thick, while the roof and rear were 6 mm, and the sides likely 10 mm. The lower rear plate was angled at 48°, while angling on other plates was inexistant or minimal. This light armor protection was a necessity to keep weight down, but penetrating hits in this section of the vehicle would obviously be much more damaging than in the cargo compartment, easily leading to the vehicle’s engine being damaged or destroyed.

Engine and Transmission

The Object 911B used the same UTD-20 diesel engine as had been used on the Object 911. This engine had previously been set as part of requirements sent to different manufacturers to produce an infantry fighting vehicle prototype and all competitors to the Object 911 also featured it. It produced 300 hp at 2,600 rpm, and reached its maximum torque output of 981 N.m at 1,500 to 1,600 rpm. Without any fuel or oil, the engine weighed 665 kg, and had a consumption of 175 to 178 grams of fuel per hp and hour. A total of 500 liters of fuel were stowed within the Object 911B.

An UTD-20 engine, which was widely used in Soviet infantry fighting vehicles and light tank prototypes from the 1960s onward. Source: https://geek-tips.imtqy.com/

An advantage of the UTD-20 was its limited size compared to its output, which was a very favorable feature for mounting it in light armored fighting vehicles such as the Object 911 or the Object 911B, allowing for the very low silhouette adopted by the vehicles. The engine was used to drive a rear transmission. The Object 911B’s transmission used a two-disc main friction clutch, composed of dry steel and asbestos, a two-flow non-differential gear and rotation mechanism, and two single-row planetary on-board gearboxes. The Object 911B used a two-shaft, 5-speeds gearbox. It was reversible, meaning the vehicle could drive with the same maximum speed and gear ratios backward. The vehicle was also capable of neutral steering.

In addition to this engine and transmission, the Object 911B also featured two hydrojets. These were found in the rear sides of the vehicle. They were taken straight from the PT-76. These hydrojets were powered via a driveshaft with a reducer, linked to the gearbox, and would allow for far quicker movement on water than vehicles using merely tracks or wheels for amphibious crossings. A trim vane could also be deployed to prevent waves from washing over the vehicle.

The Object 911B on water during its trials. This photo gives a good view of the trim vane deployed, but also of the vehicle’s radio antenna. Source: Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

Suspension and Drivetrain

The suspension of the Object 911B was directly based on the one found on the Object 911, but incorporated a number of changes. A standout feature of the Object 911 had been its four retractable aviation wheels, which allowed for wheeled drive. The advantages of such a design were higher maximum speed and reduced fuel consumption when driving on roads, which would prove useful out of combat. However, it led to increased complexity in production, maintenance, crew training, and cross-country mobility. As such, these retractable wheels were removed from the Object 911B’s design.

The Object 911 also included another innovative feature, an adjustable suspension. This was found to be less of a hassle, while at the same time having more uses, including in combat, and as such was retained on the Object 911B.

A front view of Object 911B, with its suspension likely at or close to its highest point. This photo also gives a good view of the headlights, mounted on the turret, as well as the cupola, which is not in fact crewed by the commander but the driver. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
Front schematics of Object 911B at the highest and lowest suspension setting. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The suspension of the vehicles was not exactly identical. The Object 911B was longer and had a longer track run, and as such used an additional road wheel, bringing the number to six per side. These were stamped steel hollow road wheels, the same type as used on PT-76, or at least a very similar type. Their main advantage was that their hollow construction both saved weight and improved buoyancy. Each road wheel was mounted on a suspension arm of which the movement was assured by a pneumatic suspension. The suspension’s height could be adjusted and considerably lowered. The highest ground clearance the Object 911B could raise itself to was 450 mm, which was more than any other Volgograd amphibious tank design from the era, including the PT-76 and the Object 906. When fully lowered, the ground clearance would be reduced to 100 mm. These changes in ground clearance would result in the Object 911B’s height varying from 1,625 mm to 1,265 mm. The higher ground clearance would be useful when the vehicle was driving over rough or irregular terrain, preventing risks of the lower hull being stuck on an obstacle, which would damage it or result in the vehicle losing track tension and getting bogged down and stuck. The lower ground clearance, on the other hand, would have the obvious advantage of significantly reducing the already tiny silhouette of the Object 911B. The vehicle’s drive sprocket was mounted to the rear, with a front idler. As on the Object 911, three return rollers, made of aluminum, were also present.

The tracks used on the Object 911B reportedly varied from the RMSH type used on the Object 911.

Crew compartment and turret

The crew compartment of the Object 911B was mostly in the vehicle’s turret. Both crewmembers were seated in this turret, with the driver to the right of the gun and the commander/gunner to the left. The turret had a frustoconical shape. It was of a fairly wide but very low design, differing significantly from the standardized turret featured in the Object 911.The turret rotation speed seems to have been of 30 degrees/second.

The low height of the vehicle likely resulted in the turret being quite cramped. Taking the minimum height and ground clearance of the vehicle into account, the vehicle must have been at most 1.15 m from hull floor to turret roof, not even accounting from the spacing which would exist between the floor and the seat’s bottom. This particularly low profile, though it could be commended in a way, necessitated for men of below-average height to operate the vehicle reasonably.

Comprehensive work was invested in making the crew compartment safe against nuclear threats. It was given good insulation, using special materials in addition to the steel. The Object 911B also included a radiation and chemical reconnaissance device, which would be able to measure level of radiation in an area and would be able to automatically shut the hatches if the nuclear elements that precede the shockwave of a nuclear detonation were detected.

Other equipment fitted inside Object 911B included four thermal detectors present in the cargo compartment and a further two in the engine compartment. If excessive heat was detected, these would trigger a fire extinguisher that spat out an extinguishing chemical mixture. A 2 l cylindrical container for this mixture was present in both the cargo and engine compartment.

The crew compartment featured the R-123 high/very high-frequency radio transceiver, by this point a new introduction in Soviet vehicles, which could assure communications at ranges up to 20 km on two bands. The radio antenna was on the left side of the turret. It was coupled with an internal R-124 intercom system for communications between the gunner/commander and driver. It also featured a TNA-2 navigation device and a “Brusok” encryption device for the vehicle’s outside communications. Power for this electrical equipment was provided by a 5 kW VG-7500 generator that powered two 12ST-70 batteries. 10 F1 fragmentation hand grenades, as well as a signal pistol with ten cartridges, were also stored within the crew compartment.

The R-123 radio station. Source: pinterest
An R-124 intercom system dismounted from a vehicle. Source: http://pribor.zp.ua/

Crew Positions

The gunner on the Object 911B was located to the left of the gun. Right on top of his head was a fairly large rectangular hatch he could enter or exit from.

A view of the Object 911B’s turret from the right, with the two crewmembers present inside the turret. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

Vision devices at the gunner’s disposal included a large periscope to the front and three TNPO-170 prismatic periscopes to the side. The gun was automatically loaded, but could also be loaded manually, a task he would handle if the autoloader was no longer working. Sources refer to the vehicle’s main sight as the PKB-62, with a field of view of 15° at day and 6° at night. This appears identical to the 1PN22 combined day-night sight used on the Object 911, and this may simply be two different ways of referring to the same sight. If the 1PN22 was indeed used, this sight had two channels, one for day and one for night, which would be toggled by rotating an internal mirror. The gunner would look through the same eyepiece in any case. Using the day channel, the sight had a magnification of 6x and a field of view of 15°. The night channel had a magnification of 6.7x and a field of view of 6°. It had a three-stage light intensifier system that would amplify light by 50,000 to 75,000 times. It also featured vastly simplified lead and range corrections scales in order to ease night firing.

A close-up of the seat and commands of the driver’s post. This rotating position was one of the more peculiar features of the Object 911B. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The driver had by far the most peculiar position on Object 911B. His seat, as well as the controls, were placed in a sort of ‘bathtub’. This ‘bathtub’ itself rotated within the turret. It would systematically remain aligned with the front of the tank. This was meant to allow the driver to always look straight in the position he was driving towards, but on vehicles with similar devices, such as the MBT-70, this is known to have made drivers disorientated and sick, and this may have been an issue here as well. Advantages included much better visibility for the driver, as well as, in most vehicles, resulting in less chances of crew casualties from anti-tank mines (mines would usually explode under the first road wheel, which the driver would be further away from thanks to his placement in the turret – the presence of the armored bulkhead would also grant protection against fragments). In the matter of crew survivability, the driver being in the turret could also usually escape the vehicle faster, and there would be no risk of the opening of his hatch being compromised by the gun barrel at an unfortunate time.

When reversing, this crew position was even more peculiar. A mechanism was built within the transmission gear mechanism to allow the vehicle to be driven in reverse. When wanting to reverse, the driver would be able to disconnect the clutch and pedals of his position, which t would then rotate 180°, and the controls would then be reconnected to the gearbox. In this fashion, when reversing, the driver would face towards the rear and could look straight towards where he was driving, making this essentially quite similar to driving towards the front.

A view of the Object 911B’s turret from the left, with the driver’s position shifted slightly towards the right. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
A front view of the Object 911B’s turret, with the reverse driving triggered and the driver facing to the rear. This angle also shows a good view of the vehicle’s mantlet and main gunner periscope. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

When it came to vision, the driver had three TNPO-170 prismatic periscopes as well as a TVN-2B night vision device to enable safer and easier night driving. The position’s periscopes were placed on a cupola which was slaved to the movement of the driver’s position inside the vehicle, so as with the driver’s position, they would always face in the direction the tank was driving, regardless of the turret’s position.

Armament

General schematics of the 2A28 Grom. Source: Tankograd

The main armament of the turret was a 73 mm 2A28 Grom low-pressure smoothbore gun. This was a fairly short gun, with a 2,117 mm tube and 2,180 mm total length. The design was overall made to be very simple and light. For example, it lacked any bore evacuator, and the gun fumes were instead to be evacuated from the turret, which featured a ventilator for this purpose. The gun overall weighed only 115 kg and had an average barrel life of 1,250 rounds. The recoil mechanism of the Grom was contained in an armored sleeve, wrapped around the base of the barrel. Gun elevation angles in the Object 911B extended from +30° to -3°, which was limited even by Soviet standards. The gun could elevate electrically and manually.

A number of PG-15V rounds, here captured by Azerbaijan from Armenia during the 2020 Nagorno-Karabakh War. The round was produced in massive quantities, and despite more modern ammunition to fulfill both anti-armor and anti-personnel roles, having been available since the 1970s, it is still widely used. Source: reddit

There was only a single shell type available to the 2A28 Grom in the 1960s, the PG-15V. It used the PG-9 HEAT anti-tank grenade already used by the SPG-9 73 mm recoilless gun, but swapped the original propellant charge with a more powerful PG-15P, which was meant to ensure a longer effective range. The projectile was fin-stabilized and featured a rocket engine towards the rear, with propellant present towards the middle of the grenade. This allowed it to reach a higher speed than would typically be expected from a gun as short as the Grom, with a maximum velocity of 655 m/s.

The explosive charge of the PG-9 grenade was a 322 g explosive mixture which would be equivalent to 515 g of TNT. An advantage of the PG-9 was that it featured a high standoff distance (i.e distance between the shaped charge and tip of the fuze) of 258 mm. In practice, this meant that, upon hitting a target, the jet of molten metal would have a significant length to take shape into a thin, dense jet. The results were a great armor penetration for the time and small size of the gun. The projectile’s armor penetration was officially rated at 300 mm at all ranges. In practice, this was slightly higher, as the official figure was based on the quantity of armor which would be pierced with the shell then having significant post-penetration effects inside. The maximum penetration achieved could vary between 302 and 346 mm, with an average value of 326 mm. In practice, this meant the Grom could quite reliably penetrate any tank operated by NATO in the 1960s.

The shell was not without issues, however. The downside of HEAT projectiles and a very short barrel were an overall low accuracy and high dispersion. The Grom’s PG-15V projectiles were notably very vulnerable to wind. The nominal maximum range of the Grom was of 800 m, but even at this range, only a 34% hit rate was achieved against a T-55 during trials. Even if this tank was quite smaller than most NATO tanks, in practice it can still be said a vehicle wielding a Grom would have to get to close ranges to use this gun effectively against armored targets. Additionally, during the 1960s, the PG-15V was the only available shell for the 2A28 Grom. HEAT shells are not purely anti-tank projectiles, and by nature also have some capacities against other targets. They can notably be effective when used against field fortifications and bunkers. However, due to their design focusing on producing a jet of molten metal in one direction, they offer very limited capacities when attempting to fire at infantry in the open. For the vast majority of vehicles, this would fairly easily be dealt with by simply shifting to a high-explosive fragmentation shell, but no projectile of the type would be available for the Grom until 1973.

The 2A28 Grom was fed by an autoloading mechanism. This was not the same as the crescent-shape conveyor present on the Object 911’s standardized turret design, which would contain all 40 73 mm Grom projectiles carried inside the vehicle.

While the Object 911B also had a 40 rounds ammunition stowage, its autoloader only held 27 at a time. The commander/gunner could feed more rounds into it once some were expended, or in the unlikely scenario all rounds within the autoloader were expended and no new shells had been placed into it, he could manually reload the gun as well. The autoloader mechanism was a horizontal electrically-driven conveyor belt. It would ensure a rate of fire of 9 rounds per minute. The autoloader could be installed or removed from the vehicle for repair or replacement via a special hatch.

Photos of the 7.62 mm PKT machine gun. Source: weaponsystems.net

The 2A28 Grom was supplemented by a 7.62 mm PKT coaxial machine gun. Mounted to the right of the gun, it would effectively be the only reliable means of dealing with infantry in the open. It fed to the right and ejected to the left. The PKT was fed from 250 rounds ammunition boxes and would fire at a cyclic rate of fire of 700 to 800 rounds per minute, at a muzzle velocity of 855 m/s. It would be able to expend two ammunition boxes in quick succession before the barrel would need to be replaced, or at least the firing interrupted for a bit to prevent overheating. A total of 2,000 7.62 mm rounds were stowed within the Object 911B.

Crucially, the Object 911B did not feature the 9M14 Malyutka missile or control system featured on the Object 911. This technically meant that the light tank was less armed than the infantry fighting vehicle, a considerable disadvantage. The Grom had a limited effective range, and while the Malyutka was not the most accurate or reliable missile, it was still a much better weapon to take out armored targets at longer ranges. Without the Malyutka, the Object 911B could only engage enemy armor within the reduced effective range of the Grom.

Trials and Performances

The Object 911B prototype was completed and trialed in 1964.

The vehicle was able to reach a maximum speed of 72.5 km/h on road. This was a considerable improvement from the Object 911 which would only manage 57 km/h on tracks. The main reason likely was the removal of the extendable wheels and changes to the suspension. On water, the vehicle could reach a similar maximum speed of 10 km/h, which was generally the norm for vehicles equipped with the PT-76’s hydrojet design. The maximum range on road was 500 km, similar to the Object 906 and exceeding the PT-76. Ground pressure was 0.42 kg/cm².

Object 911B at its lowest suspension height next to a PT-76B during its trials. The low profile of the vehicle at the lowest suspension setting was exceptional. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

The vehicle’s armor protection was tested against two different threats. The first was against 76.2 mm projectiles fired at ranges of 2,000 m with a muzzle velocity of 665 m/s. These were likely kinetic projectiles fired from the PT-76’s D-56T (this velocity matches with the BR-350B and BR-354 APBC-HE shells, the latter of which was more common by this point in time). The frontal crew compartment armored bulkhead and turret armor were both found to resist penetration at this range. These were satisfactory performances. While the D-56T was not a very powerful gun and the projectiles were fired at a long range, a light amphibious tank is not a vehicle that is expected to resist armor-piercing weapons at pretty much any range, and indeed many vehicles fulfilling a similar role, such as the PT-76 or M551 Sheridan, would still be fairly easily penetrated even at this range.

More representative of the armament a light tank with good armor protection for the type may be expected to resist, the Object 911’s crew compartment was also tested against the 14.5 mm KPV. The weapon failed to penetrate both the front bulkhead and the hull sides. This was once again quite a considerable feat. The 14.5 mm KPV was one of the most powerful mass-produced heavy machine guns around, and if the Object 911B’s crew compartment was impervious to it, it would certainly resist NATO’s .50 cal Browning M2HB. In certain conditions, such as with some range and with imperfect firing angles, which are to be expected in combat, the crew compartment of the Object 911B may have stood decent chances to resist fire from many NATO autocannons of calibers around 20 mm, which would be an impressive performance for a light amphibious tank.

Conclusion – Interesting Performances with no Niche to Fulfill

Ultimately, the Soviet Army did not adopt the Object 911B, and work on the vehicle was discontinued after the trials ended in 1964.

A number of reasons can be found for the rejection of the vehicle. The most obvious was that the original Object 911 was not picked to become the BMP-1, being ruled out of the candidates due to complications with its drivetrain fairly early on. The other Volgograd prototype, the Object 914, was a more serious candidate but was eventually rejected in favor of the Object 765, which would become the famed BMP-1 that remains widely in use across the world today. There would have been little motivation in adopting a light tank derived from an infantry fighting vehicle which was rejected. Even though the Object 911B had significant parts commonality with vehicles already in service, such as the engine, road wheels, or armament, it would still lead to increased logistical complexity.

However, outside of these external considerations, the Object 911B had faults of its own. Some aspects of the vehicle were genuinely quite impressive, with the exceptionally low profile at the foremost. The armor protection given to the crew was also significant for a vehicle of the type. The crew of an Object 911B would have much more chances to survive enemy fire than the one of another amphibious light tank, such as the previous Soviet PT-76, the American M551 Sheridan, or the British FV 101 Scorpion fitted with a floatation device. Being able to resist heavy machine-gun fire or even light autocannons is significantly better than most vehicles of the type and would protect the Object 911B’s crew from some widely-encountered threats. This level of protection only extended to the crew, with the cargo and crucially engine compartment only being protected against rifle-caliber projectiles, but it was still significant.

The Object 765 prototype, which would be adopted and become the BMP-1 in 1964. With this vehicle already scheduled for production, there was little need for the Object 911B. While one may point to several advantages of the Object 911B in terms of survivability, this was not as strong as an argument in comparison to the eight dismounts and 9M14 Malyutka missile sported by the BMP. Source: Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3

However, the vehicle’s firepower was far too low to justify its existence. The Object 911B was only armed with the same 73 mm 2A28 Grom as the BMP-1 and a coaxial machine gun, and its lower profile and better armor protection could hardly create the need for it. In comparison, the BMP-1 would not only transport eight dismounts, but also feature a 9M14 Malyutka missile, which means it would be far better equipped to deal with enemy armor at range. Indeed, for all of the Object 911B’s advantages in survivability granted by its low profile and armor protection, these would be in large part negated by the need to be at small ranges for the Grom to have a good chance to hit enemy targets. At those ranges, enemy guns would have far lower difficulty to target the smaller profile of the Object 911B, and the vehicle would likely fall prey to most tanks before it could be at short enough range to target them unless it could be undetected until the moment it fired. While this would be easier for the Object 911B than pretty much any other tank, it is still not something to be relied upon, particularly if the vehicle was to be used offensively. The issues of disorientation that could arise from the driver’s placement in the turret were also not resolved.

In short, while very interesting in several aspects, the Object 911B did not fulfill any niche where a vehicle of its kind was necessary, and as such it is not surprising it was not adopted by the Soviet Army. Unlike the Object 911, the Object 911B does not appear to be preserved at the Kubinka Tank Museum, or at least not in its visitable parts, as no modern photos of the vehicle have emerged. It may have been scrapped, or still be preserved outside of public view.

Object 911B, illustrated by Pavel “Carpaticus” Alexe

Object 911B specifications

Dimensions (L-W-H) 7.100 x 2.800 x 1.625 to 1.265 m
Ground clearance 100 to 450 mm (adjustable)
Combat weight 12.5 tonnes
Engine UTD-20 6-cylinders 300 hp diesel engine
Suspension Adjustable pneumatic springs
Transmission mount rear
Forward gears 5 (reversible)
Road wheels 6
Maximum speed (road) 72.5 km/h
Maximum speed (water) 10 km/h
Range 500 km (road)
Crew 2 (driver, commander/gunner)
Gunner’s vision devices Main periscope
3 x TNPO-170 prismatic periscopes
PKB-62 (1PN22 ?) sight
Driver’s vision devices 3x TNPO-170 prismatic periscopes in a rotating cupola facing towards the direction the vehicle is driving in
TVN-2B night vision device
Main gun 73 mm 2A28 ‘Grom’ with 40 rounds (27 stowed in autoloader)
Autoloader Electrically-driven horizontal conveyor belt
Secondary armament Coaxial 7.62 mm PKT with 2,000 rounds
Hull armor Cargo compartment:
10 mm/45° (front)
4 mm (floor)
6 mm (roof)
Likely 10 mm (sides)Crew compartment:
35 mm (front bulkhead)
45 mm (upper sides)
20 mm (lower sides)
35 mm (rear bulkhead)
10 mm (roof and floor)
Turret:
40 mm /40° (front)
40 mm /30° (sides)
Likely 40 mm (rear)
10 mm (roof)
Engine compartment:
4 mm (floor)
6 mm (roof and rear)
Likely 10 mm (sides)
Effective protection of crew compartment 76.2 mm projectile fired at 665 m/s and a range of 2,000m (front bulkhead and turret)
14.5 mm KPV fire from all angles
Numbers produced 1

Sources

Solyankin, Pavlov, Pavlov, Zheltov. Otechestvennye boevye mashiny vol. 3
73-мм ГЛАДКОСТВОЛЬНОЕ ОРУДИЕ 2A28Техническое описание и инструкция по эксплуатации (73-mm SMOOTHBORE WEAPON 2A28 Technical description and operating instructions)
БОЕВАЯ МАШИНА ПЕХОТЫ БМП-1 ТЕхничЕскоЕ ОПИсаниЕ И ИНСТРУКЦИЯ ПО ЭКСПЛУАТАЦИИ (COMBAT VEHICLE INFANTRY BMP-1 Technical Description AND THE OPERATING INSTRUCTIONS)
BMP-1 field disassembly, Tankograd
skylancer7441’s archive

Categories
Cold War Soviet Prototypes

Object 715

 

USSR (1946-1947)
Heavy Self-Propelled Gun (SPG) – Partial blueprints only

The Object 715 was a heavy self-propelled gun based on the chassis of the IS-4 developed by SKB-2 at Kirov Chelyabinsk plant (ChKZ). A direct successor to the Object 704, in turn based on the IS-3, the Object 715 never even had full blueprint studies before the design was canceled due to the shifting in military philosophies, with heavy gun platforms falling out of favor with militaries across the world.

Background and Development

The end of war usually indicates a moment of peace and joy, and in tank-related terms, the cancellation of many designs and projects. However, the end of the Second World War could not have been any more different. The clear political and military tensions between the USSR and Western nations meant that tank development never really halted after the defeat of the Axis powers. As a matter of fact, the Soviets invested heavily into more powerful tanks. So much so that many programs overlapped with each other, such as the IS-3 and IS-4 heavy tanks for the SKB-2 (design bureau of the Chelyabinsk Kirov plant) alone.

Surviving IS-4M heavy tank.
Source: Pinterest

The IS-4 (designation Object 701), like the IS-3, was meant to replace the IS-2 heavy tanks. Envisioned to be the pride of the Soviet tank forces, the IS-4 was given extremely thick armor, weighing 53 tonnes, and driven by a 750 hp V-12 diesel, allowing it to reach up to 43 km/h. But despite being an upgrade to the IS-2, it never brought much to the table, especially when compared to the IS-3, a lighter, faster, and cheaper tank that, just a couple of years earlier, had shocked the Western world.

Most importantly, the IS-4 had the same 122 mm D-25T gun like the IS-2 and IS-3. Production started in March 1947 and ended just a couple of years later, in 1949, when all activity on tanks weighing over 50 tonnes was canceled. The tank proved to be too heavy and sluggish and poorly constructed. Another small batch of 25 units was built in 1951 with some upgrades, called IS-4M. All previous tanks were upgraded to this level. In total, only 258 were built.

During the IS-4’s development process, an SPG variant was also designed. SKB-2 had done something similar just a couple years earlier, designing the Object 704 SPG right after the IS-3 (Object 703). One prototype was built in spring 1945 and tested in the autumn of that year. State trials of the Object 704 revealed several issues with the SKB-2 SPG. The iconic sloped armor sides severely decreased the space available inside the crew compartment, hindering the loader from accessing all the shells properly, and the breech operator’s position was very tight, having a hard time extracting the explosive charges. This also led to a rather limited ammunition count. Trial officers recommended that the walls were to be made vertical again, like on the ISU-152.

The single prototype built of the Object 704 survives today at Kubinka, where it was brought for testing in 1945. Source: World War II Wiki

An exact timeline of the development of the Object 715 is hard to establish. At some point during 1946, work began on the Object 715, when interest from the state in heavy SPGs armed with 152 mm guns grew again. SKB-2 would base this SPG on their new IS-4, which had gotten far in development. Interestingly, their rival, the Kirov plant in Leningrad, also got far with their designs on the Object 260 (IS-7) heavy tank and based their SPGs on this chassis.

Purpose

The versatility that heavy SPGs showed during the Second World War had greatly impressed the Soviets. Their large-caliber guns, whether 122 mm or 152 mm, were powerful enough to deal with almost any kind of threat. Casemates, machine gun nests, and other static defenses, would be deleted from the face of the earth, doubling down as iconic propaganda machines to this day. Even the heaviest German tanks would prove vulnerable to a direct hit from a 152 mm shell, cracking open welds and rupturing armor via pure momentum and force.

Deep Battle doctrine, a complicated and much-debated philosophy from the first Soviet use of tanks, proved to be effective after the Axis’ defeat. Here, self-propelled guns would prove important and critical in weakening enemy defenses prior to an attack, but support infantry and tanks with unparalleled firepower. Theoretically, such self-propelled guns would target remaining enemy troops after indirect fire shelling, which would allow the infantry to push along with the ‘regular’ tanks. But reality pushed these vehicles to adopt a more aggressive style of combat, acting a lot more like an assault gun. The ISU-152’s armor proved insufficient for such purposes, which was why the Object 704, at first designed at the beginning of 1945, focused greatly on protection, with thick, angled plates across the casemate.

But after the war, the philosophy and environment changed. Raw armor thickness simply would not cut it. Battle tanks had increasingly more powerful guns and warfare got more mobile. To cope with these changes, designers had to increase the engagement distance of SPGs, in turn allowing for less armor. New medium and heavy tanks, both domestic and foreign, proved to be more and more self-sufficient in all areas. Self-propelled guns were no longer needed on the first line of attack and could afford to cut down on protection by engaging from as long ranges as possible. This would have required a seriously powerful gun.

Design

The design of the Object 715 was almost identical to that of the Object 704. The front of the vehicle was dominated by a large gun mantlet. This mantlet was a redesign of the one found on the Object 704, where water used to gather into the gap beneath the mantlet, meant to allow the mantlet to depress the gun. On the new design, the mantlet was depressed straight into the fighting compartment, and protected by an outer sleeve along the sides. The roof was also redesigned to allow the gun to depress more.

Only available blueprints of the Object 715. The gun shown is likely a modernization of the M-31 152 mm, sometimes called the M-48.
Source: Tank Archives

The most noticeable feature of the new SPG was the small volume of the casemate. The new armament had almost 3 times less recoil distance compared to the Br-2 howitzer. This allowed the designers to shorten the casemate significantly. The blueprints also show the lower hull of the IS-4 chassis, which has been altered to fit the casemate. Of great interest is the armor thickness of the lower plate, or lack thereof. Despite these changes, the blueprints of the Object 715 perfectly match and fit into those of the IS-4. The exact mass is unknown, but some sources claim 60 tonnes. While not impossible, this meant that it would have been heavier than the IS-4 itself.

Using the IS-4 chassis, most mechanical components remained the same.The engine was a V-12 diesel outputting 750 hp at 2100 rpm, coupled to a 6-speed forward, 2-speed reverse manual gearbox.

Crew

Soviet tanks are not known to have vast and lavish crew spaces, and the Object 715 would have been no exception. This trend began with the pressures of the war in the 1940s, forcing designers to make sacrifices. This issue continued until the 1950s, from which point crew ergonomics improved greatly.

The crew likely consisted of 5: commander, gunner, driver, loader, and loader assistant (formerly breech operator), all cramped in a small casemate. They were positioned in the classical formation, with the driver on the left side of the gun, controlling the tank with two tillers. The driver had one MK-4 periscope for vision outside, increasing his reliance on the commander for directions. Communication within the tank was done via a TPU-4F intercom, with headset and microphone. While it is hard to prove, it is very likely that each crewmember had their own entry and exit hatch, like on the Object 704. Shared hatches would have been very cumbersome, as the gun took up a lot of space.

The gunner was seated behind the driver, on a small seat, attached close to the gun breech. For vision, the gunner had the main gun sight, a TP-47A, and a secondary horizontal (azimuth) ZIS-Z sight was also provided, for indirect fire. It protruded from the hull and was protected by an armored housing. Hand crank controls for elevation were also available for the gunner. Like on previous SPGs of this type, aiming the gun was a team effort, with the gunner controlling the elevation, and the traverse being controlled by the breech operator sat behind him. This was the unfortunate outcome of letting the individual tank factories design the horizontal traverse and not the gun factory (Factory No.172).

In previous vehicles, the breech operator was tasked with opening the breech, controlling the gun traverse and loading ammunition charges. The shells, although being two-part rounds consisting of charge plus shell, weighed between 43.56 kg and 48.78 kg. For this reason, it was deemed necessary to include a loader assistant that would remove some of the strain from the loader. Exact crew positions and the ammunition layout are not present in the drawing, but judging from previous similar vehicles, the ammunition was stored on the sidewalls, with the projectiles on the right wall and charges on the left.

The loader sat opposite to the loader assistant, on the other side of the breech. The loader was tasked with loading the shells and firing the coaxial machine gun, likely a 12.7 mm DShK, and operating the potential external anti-aircraft machine gun, also an 12.7 mm DShK (not featured on the partial blueprints).

Finally, the commander sat in front of the loader, to the right of the gun. The commander’s main task was coordinating the crew, scanning the battlefield, and communicating with other units via the 10PK-26 radio, with a stationary range between 20 km to 25 km.

Armament: the M-31 and M-48 152 mm

At first, the armament was to be a 152 mm gun developed at factory No. 172, the M-31. The ballistics were mostly identical to those of the regular M1935 Br-2 howitzer, but with considerable upgrades in other areas. Firstly, the archaic breech block door was replaced with a more modern horizontal sliding breech block. It also received the famous TsAKB style slotted muzzle brake, which could absorb up to 70% of the recoil, decreasing the need of powerful recoil adsorption pistons. It still had two recoil absorption cylinders and two brake cylinders to absorb recoil, but these were considerably lighter, and in tandem with the muzzle brake, decreased the recoil from 1,400 mm (on Br-2) to 520 mm. Other improvements were an automatic barrel smoke evacuator, and the TP-47A direct fire sight, and ZIS-Z sight for indirect fire. Very noticeable is the sheer volume of the breech which was needed to offset the long barrel. One prototype of the gun was built and passed factory tests in the summer of 1948.

The M-31 gun was incorporated into the Object 715 in late 1947, however, the original plans of the Object 715 were rejected by the military, sending the SKB-2 designers back to the drawing board. The complaints came from the integration of the gun into the IS-4 chassis. It was seen as cumbersome, tight and hard to coordinate. Meanwhile, Plant No.172 developed an upgrade of the M-31, the M-48.

Plans for the M-48 were submitted for review to the Soviet state by plant No.172 on 9th August, 1946, which were approved in November. It increased muzzle velocity to 1,000 m/s and featured a slotted muzzle brake with an efficiency of 59%. A horizontal semi-automatic breech block was also designed in two versions, pneumatic and mechanical. The final draft of the gun was submitted on the 21st of June 1947 and approved for prototypes and testing. Three were built and tested. From here onwards, what happened to Object 715 is unclear. When exactly and how the M-48 was incorporated remains a mystery. It is possible that it was rejected once again, or the project was shelved for a future request, with work switching to other areas.

As secondary armament, the Object 715 had a 12.7 mm DShK heavy machine gun, loaded by the loader.

Armor

As the new weapons that were proposed allowed for greater engagement distances, the armor became less relevant. Any excessively thick armor, combined with the massive guns with great overhang, and the IS-4 chassis simply could not have handled the stress on the first set of torsion bars. Thus, the armor was made thinner but more angled. However, this was not to the extreme seen on the Object 704. The frontal plate was 100 mm thick angled at 45°. The lower plate was around 30 mm angled at -40°. Side and cheek armor values are unknown. The rest remained the same as on the IS-4 tank.

Fate

Plant No.172 agreed with the Kirov Chelyabinsk SKB-2 plant to use the M-31 in the Object 715, but also with Kirov Leningrad to use the same gun on their Object 261/Object 263 SPGs based on the IS-7, once again leading to a direct competition between the two rival factories.

In addition, Plant No.172 presented on 23rd August, 1948, a new upgraded gun, especially designed for the IS-7 based SPGs, which would eventually use the 130 mm S-70 gun. Regardless of how far these programs went, they were all canceled on 16th February, 1949, when the Council of Ministers of the USSR canceled all tank development above 50 tonnes. The concept of Heavy SPGs was once again considered with the Object 268 program, from where they would be sealed off for good.

Conclusion

While it was one of the most powerful direct fire SPGs ever designed, the shortcomings of the IS-4 platform and the shift from large guns on heavy chassis to other design philosophies, such as ATGMs, led to its demise. The Object 715 remains, to this day, one of the more mysterious Soviet post-war designs, with nothing but a half-drawn blueprint remaining.

Object 268 final version, which resembles the Object 715, despite being designed and produced by Kirov Leningrad a few years later.
Source: Google Sites
Artist interpretation of the Object 715, as per the blueprints. Illustration by Pavel Alexe.

Object 715 specifications

Dimensions (L-W-H) 6,682 (hull only) x 3.26 x 2.4 m
Total Weight, Battle Ready circa 50 tonnes
Crew 5 (Commander, Gunner, Driver, Loader & Breech operator
Propulsion V-12 Diesel engine, 750 hp
Speed 40 km/h (hypothetical)

(25 mph)

Armament 152.4 mm M-31 howitzer

or

152.4 mm M-48 howitzer

coaxial 12.7 mm DShK heavy machine gun

Armor Hull armor:

Front top plate: 100 mm at 45°

Front bottom plate: 30 mm at -50°

Top: 30 mm

Belly: 30 mm

Total Production 0; blueprints only

Sources

Domestic armored vehicles 1945-1965 Soljankin, A.G., Pavlov, M.V., Pavlov, I.V., Zheltov
Technics and weapons (TiV) 1996 06, M.V. Pavlov, I.V. Pavlov
Tank Archives: The Last Soviet Heavy Tank Destroyers
The genius of Soviet artillery. Triumph and tragedy of V. Grabin – Shirokorad Alexander Borisovich

Categories
Cold War Soviet Prototypes

K-91 SPG

Heavy SPG- Soviet Union
(1949) Blueprints only
Pavel Alexe

Many heavy Soviet self-propelled guns (SPGs) were based, in some form or another, on a heavy tank. This format was used extensively during the Second World War and became standard post-war. Any heavy tank would serve as the chassis for an SPG as well. So naturally, when all heavy tanks weighing 50 tonnes and more were cancelled in early 1949, many SPGs were ended as well, like the case of the IS-7 and Objects 261 to 263. But this cancellation made space for new, lighter, heavy tanks and SPGs, like the K-91 tanks.

Development

The Council of Ministers of the USSR released decree No.701-277§ on 18th February 1949, ordering that all heavy tanks weighing over 50 tonnes were to be canceled. This gave an opportunity to the Design Bureau of the Engineering Committee of the Armed Forces (OKB IC SV), led by Anatoly Fedorovich Kravtsev, to develop three vehicles – two heavy tanks and an SPG. The vehicles were supposed to replace both heavy and medium tanks, and offer a good platform for an SPG.

The first K-91 proposal, with a frontal mounted turret and engine at the rear.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 34

Design

The K-91 SPG was largely based on the K-91 heavy tank with a frontal mounted turret. The hull remained almost unchanged, with the exception of the rear, which had to be altered to fit the rear mounted casemate. This was made out of eight thick welded armor plates, heavily angled from all sides to increase armor effectiveness. The main 100 mm gun was fixed into this casemate and had limited traverse. Like on the previous K-91 heavy tanks, the driver was not situated in the hull but moved up into the casemate. The casemate was mounted to the rear of the vehicle to minimize gun overhang and make the vehicle more maneuverable in city streets or forests. However, such a layout had proven to be faulty before as the heat from the engine could damage the barrel or distort the view through the gun sight.

Curiously, the design is very similar to Shashmurin’s IS-2 based SPG and also the much later Object 268 versions 2 and 4. Shashmurin most likely never had any involvement in a OKB IC SV vehicle, and he was generally a rival, as he worked at Chelyabinsk.

Equally bizarre, when the K-91 SPG was introduced into the game World of Tanks, it was named K-91 PT. The acronym ‘PT’ comes from the romanized Russian word ‘protivotankoviy’, meaning anti-tank. This is not entirely historical, as such vehicles were mostly called SU or SAU, from the Russian ‘Samokhodnaya Ustanovka’, essentially meaning self-propelled gun.

Side view of the K-91 SPG
Source: Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 35

Crew

The SPG had a crew of 4: commander, gunner, driver, and loader. They were all seated in the casemate.

The gunner sat to the left of the gun. He had controls over the main armament and possibly the secondary coaxial machine gun, if there was any. For vision, he could only use his main gun sight. The commander was seated behind him, albeit higher up. He had a small protrusion from the casemate roof, just big enough to fit the top of his head. There, the single periscope was mounted. Although it was placed quite high up, a single periscope offers atrocious visibility, especially for a vehicle that lacks a turret. It is unclear if it could rotate or not. The commander was likely also in charge of the AA 12.7 mm DShK machine gun. It was mounted on a swivel pintle mount, like on the IS-3 and IS-4. The commander could exit and enter through his small dome, which had a hatch. It is unclear if the gunner also used this hatch or if he had his own.

On the right side of the gun sat the driver. He was also seated quite high up and had his own little protrusion with a hatch, but smaller than the commander’s, which also had a single periscope. The driver could enter and exit via this hatch. Behind the driver, but lower into the body of the vehicle, behind the gun breech, was the seat of the loader. He had full access to the ammunition stored on the right side of the vehicle but had to stand up or get help from the commander when hauling shells from the left side.

Rear cutout view of the K-91 SPG. Note the layout of the engine and ammunition.

Armament

The main armament of the K-91 vehicles was to be a 100 mm D-46T. The development of this gun started on 28th May 1948, and two prototypes were built in 1949 at Factory No.9. It was meant to replace the wartime D-10T gun, but the entire project was canceled shortly after. The ammunition consisted of a single piece, weighing 16 to 17 kg, with a muzzle velocity of 1,000 m/s.

This was the same gun used on the heavy tanks, so the SPG variant did not offer a large advantage over the heavy tanks, one of which was autoloaded and both of which had turrets. There could have been a difference in ammunition loadout, but neither the gun nor the vehicles got far enough in development for this to be a serious issue. Rounds were placed vertically across the side and rear fighting compartment walls, and several stowed horizontally in the hull. The gun was enclosed in a limited traverse mount. It had +20° of elevation and -3° of depression. Horizontal gun traverse is unknown, but judging by the space inside the fighting compartment, around 10° in both directions seems plausible.

Two secondary armaments were probably used, a pivoting pintle-mounted AA 12.7 mm DShK machine gun, and potentially a coaxially mounted DShK as well.

Propulsion

The powerplant of the vehicle was to be a V-64 12 cylinder boxer diesel engine mounted in the front of the hull. In front of it were the transmission and final drives coupled to the large frontal drive sprockets. Boxer engines feature horizontally mounted pistons acting against each other on a crankshaft in the middle. This allows for far shorter engines, but also much wider compared to the usual in-line or V-shaped engines.

Armor

Being based on the K-91 heavy tank, the armor was very good. The upper frontal plate was 200 mm thick, angled at 45°, The lower frontal plate was 150 mm angled at 50°. The side armor was flat and 150 mm thick. The front of the casemate armor was 200 mm thick on the front (60° angle) and cheeks. The side was 120 mm, angled at 60°. The rear was around 100 mm thick, also angled at 60°.

Conclusion

Unless some drastic changes were made to the ammunition or main armament, the K-91 SPG was made obsolete by the other K-91 heavy tanks. The entire K-91 program proved to be unsuccessful and was canceled in December 1949 as the vehicles were deemed to not bring a big advantage over existing medium and heavy tanks.

Object 268 Version 4, on December 18, 1952.

After the end of developments of IS-7 and other heavy tanks, and SPGs based on them, heavy SPG development stopped in the USSR. The concept would be revived, unsuccessfully, for the last time in the 1950s, with the Object 268 program, of which, versions 2 and 4 were very similar to the K-91 SPG.

Illustration of the K-91 SPG, speculating how it might have looked like. By Pavel Alexe, funded through our Patreon.

K-91 SPG specifications

Dimensions (L-W-H) in mm 8,780 (6,570 w/o barrel) x 3,340 x 2,200
Total Weight, Battle Ready circa 49 tonnes
Crew 4- commander, gunner, driver, loader
Propulsion V-64 boxer 12-cylinder diesel, est.700-800 hp
Armament 100 mm D-46T
co-axial 12.7mm DShK
AA 12.7 mm DShK
Armor 200 mm front casemate
120 mm side casemate
200 mm UFP
150 mm LFP, cheeks, side
Total Production None; paper design only

Sources

Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965
Yuri Pasholok on the Soviet STG – Status Report (ritastatusreport.live)
https://military.wikireading.ru/56371

Categories
Cold War Soviet Prototypes

K-91 (Rear mounted turret)

Heavy tank – Soviet Union
(1949) Blueprints only

After the Councils of Ministers of the USSR had terminated all heavy tank projects of 50 tonnes and more in 1949, many Soviet design bureaus and factories saw their opportunities to design new vehicles. One of these was OKB IC SV (Design Bureau of the Engineering Committee of the Armed Forces) led by Anatoly Fedorovich Kravtsev. They designed three vehicles, two heavy tanks and one SPG, under the name K-91.

Development

The Councils of Ministers of the USSR stated on 18th February, 1949 in the decree No.701-277§ that all design, development and production of heavy tanks heavier than 50 tonnes shall end. Kravtsev’s team at OKB IC SV set to work almost immediately to design some lighter heavy tanks that would replace both heavy and medium tank classes, whilst also being the platform for Self-Propelled Guns (SPGs). The lead engineer was I.T. Levinov and the designer was Matyukhin.

The bureau designed three vehicles, named K-91. The first was a heavy tank with a large, front-mounted turret that encompassed all 4 crewmembers. The second was a rear-mounted turret heavy tank that featured an odd-shaped hull and an autoloader. There was also an SPG.

Design

The second variant of the K-91 heavy tank design was less elaborately depicted than the first (there is no knowledge on the chronological order in which the tanks were designed, and are numbered as such simply to differentiate them). From the 4 available drawings, the tank had the turret mounted in the rear of the hull and the engine and transmission were mounted all the way in the front. This offered a lot more protection to the crew, as the mechanical components acted as a form of armor against fragments following penetration. The crew, consisting of 3 men, were all seated in the turret. Most curiously, the hull had a very odd shape. From above, it was almost shaped like an egg, while from the side, it was flat. This awkward hull design, combined with the stowage of ammunition in the turret, resulted in a lot of empty space in the hull.

Side view of the K-91 rear-mounted proposal. From this angle, the hull seems very flat and unremarkable.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 35

Crew

As aforementioned, the tank had a crew of 3; commander, gunner, and driver. They were all seated in the turret. The gunner sat on the left side of the gun and only had his main gun sight as vision, having to rely entirely on the commander’s calls. The commander sat right behind him, surrounded by the ammunition, and had only one periscope to view out of. He had a protrusion from the otherwise semi-spheric turret, akin to a commander cupola. This is where the periscope was mounted and, most likely, this was his entry and exit hatch. The gunner most likely also used this hatch. The commander was close to the gun breech, potentially meaning that he could manually load the gun if the automated system failed.

Lastly, the driver was seated on the right side of the gun. Since he was seated in a rotating turret, he was given a pivoting device that would allow him to remain facing the front of the hull regardless of the rotation of the turret. This, however, makes it unclear if the turret was able to perform a full 360° rotation. Right behind him was the plethora of ammunition. Since the driver was placed quite high in the turret, he also had a protrusion from the rounded cast turret.

From this angle, the bizarre, almost UFO-like hull shape is clear. Despite it having no vertical angling, the Z-axis angling gave it very good LOS protection.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 35

Armament

The main armament on the K-91 heavy tanks was to be a 100 mm D-46T. At the point when these tanks were designed, this was a brand new gun. The project started on 28th May, 1948 and it was intended as a replacement to the D-10T gun used on the T-54. Two prototypes were built at Factory No.9 in 1949. Development was canceled shortly after though, but it was important in the development of the D-54.

The ammunition had a muzzle velocity of 1,000 m/s and weighed between 16 to 17 kg. The ammunition was not two-part, despite being very large. The gun had +12° of elevation and -3° of depression.

While the frontal mounted turret variant featured a human loader, the rear-mounted turret K-91 had an autoloader. However, no details are provided and the drawings do not offer any details on the mechanism. Autoloaders were still in a relatively infant stage, especially at such large calibers. The Soviets had some experience with autoloaders, as they had experimented with such devices on tanks even during the war, and the final variant of the IS-7 featured an autoloading mechanism for the massive 130 mm main gun. However, the system on the K-91 was different from that on the IS-7, which featured two-part ammunition stored in a rack, and were pushed in by a conveyor belt. The gun required to be brought back to neutral position after each shot. The K-91 system featured ammunition stowed all across the turret being pushed in towards the center. There, a conveyor belt or arm would ram the shells in. Since the ammunition was one single piece, reloading would have taken less time.

The tank had one secondary armament, a 12.7 mm DShK heavy machine gun, mounted coaxially.

The autoloading mechanism on the IS-7.
Source: Pinterest

Propulsion

When moving the turret to the back, the engine was moved to the front, right behind the transmission (the drive sprockets were in the front). The specific engine used was, allegedly, a V-64 12-cylinder boxer diesel. Boxer engines have pistons mounted horizontally, facing away from each other. This makes them a lot lower (it allowed the hull to only be 1,170 mm tall), but wider than other piston configurations, such as in-line or V-shaped. In this case, the width did not matter due to the large amounts of empty space next to and behind the engine. The position of the fuel tanks is unknown. They could either have been in front of the turret cheeks, which was the furthest possible spot from the engine, or between the basket turret floor and tank floor, between the torsion bars.

Rear cutout view of the K-91 with a rear turret. The wide boxer engine can be seen, with the gun and massive diagonally mounted 100 mm shells.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 35

Armor

In terms of armor protection, the tank had plenty. The thickest was around 260 mm. However, this spot was rather small, as it was only the ‘tip’ of the hull. This thick piece of armor was bent into shape and then connected to the rest of the hull armor via a puzzle connection weld. The rest of the hull was 200 mm all throughout. These seem to be entire sheets of armor that were bent into shape. The frontal lower plate seems to have been 100 mm thick, although angled at -40°. The rear armor plates were even thinner, probably around 75 mm. The belly armor was 10 mm and top 20 mm.

The turret was a classic Soviet-style semi-sphere, with the addition of the two domes for the driver and commander. The turret seems to have been 200 mm thick all around, with only various mantlet and roof areas being thinner.

Side cutout view of the vehicle. Here, the armor layout is well visible.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 35

Suspension

Although it is different compared to most Soviet heavy tanks of the time, the suspension was fairly standard. It featured a small frontal mounted sprocket, 9 roadwheels sprung to 7 torsion bars and a rear idler. The first two and last two wheels were connected to each other and were attached via a bogie.

Other K-91s

As previously stated, Kravtsev’s team proposed three vehicles. Besides this one, there was a frontal mounted turret heavy tank and an SPG. The video game company Wargaming took this variant and the frontal mounted turret version and created an unhistorical hybrid.

Conclusion

Despite having some more technologically advanced features over the other K-91 variant, such as an autoloader, the design never got very far and all K-91 projects were canceled later in 1949, most likely as they did not bring any realistic improvement over existing and future combat vehicles.

K-91 rear-mounted turret specifications

Dimensions (L-W-H) 9,020 m (7,650 m w/o barrel) – 3,350 m – 2,140 m
Total Weight, Battle Ready circa 49 tonnes
Crew 3- commander, gunner, driver
Propulsion V-64 boxer 12-cylinder diesel, est.700-800 hp
Speed N/A km/h
Armament 1x 100 mm D-46T autoloaded
1x co-axial 12.7mm DShK
Armor 200 mm around turret
260 mm front tip
100 mm lower frontal plate
200 mm hull side and cheeks
75 mm rear hull
Total Production none – paper only

Sources

Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965
Yuri Pasholok on the Soviet STG – Status Report (ritastatusreport.live)
https://military.wikireading.ru/56371

Categories
Cold War Soviet Prototypes

K-91 (Front mounted turret)

Soviet Union (1949) Heavy tank – Blueprints only

With the end of the Second World War (Great Patriotic War in Russia) and the uncertainties of a new war, many nations sought to design weapons as revolutionary and powerful as possible. This often involved thinking outside the box, resulting in some odd and interesting designs. One of these projects was the K-91, born at a time when the Soviet Union had a hypersaturated market in regards to general tank development and especially heavy tanks.

Development

On 18th February, 1949, the Council of Ministers of the USSR published statement No.701-277§, which effectively canceled all development of heavy tanks weighing 50 tonnes and above, putting an end to tanks such as the IS-7. Instead, work was shifted to designing lighter heavy tanks. Thus SKB-2 and Factory No.100 of Chelyabinsk were assigned work in designing a new heavy tank, which would eventually become the T-10.

With the cancellation of most heavy tanks programs, the Design Bureau of the Engineering Committee of the Armed Forces (OKB IC SV), led by Anatoly Fedorovich Kravtsev, saw the opportunity to design a unique set of vehicles. By this point, Kravtsev’s design bureau had experience in designing light tanks and APCs, but never had them mass produced, such as the K-75. Kravtev’s team envisioned something special. This was not to be any regular heavy tank, rather, they would look back at wartime vehicles which tried to combine and replace both medium and heavy tanks, while still being a solid platform for self-propelled guns, a concept that became mainstream later on.

In charge of the program was lead engineer I.T. Levinov while the designer was Matyukhin. They designed three vehicles: two heavy tanks, one with a front mounted turret, one with a rear mounted turret, and a tank destroyer/self-propelled gun. In this article, the first variant will be discussed.

The first K-91 proposal, with a frontal mounted turret and engine at the rear.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 34

Design

The first variant, besides being the most sensible, was also the one that was considered the most, with a total of 5 drawings. It featured a massive turret that housed all 4 crewmen – including the driver. The hull was extremely low, thanks to the movement of the driver to the turret and usage of a boxer engine. This was done not only to decrease the area and silhouette of the vehicle, but also to make it lighter and harder to hit. The bizarre aura of the vehicle continues, with a very strange set of roadwheels, with torsion bar suspension and a large frontal sprocket. To create more room inside the tank, the sides of the hull follow the shape of the track, which required the addition of round skids to prevent the track from hitting the hull violently. The armament would be a modest 100 mm gun with a coaxial DShK and one more on the roof for AA protection. In terms of protection, however, the tank stood out, with around 200 mm of raw thickness on the upper frontal plate and turret.

Crew

The crew consisted of 4 men, a commander, a gunner, a driver, and a loader. They were all seated in the turret. The gunner sat on the left side of the gun, in the front of the turret. He had no periscopes, but had to rely on his gunsight for vision. Considering the shape of the turret, which featured two unevenly sized bulges protruding from the otherwise rounded turret, the gunner had to share the entry and escape hatch with the commander. The commander sat right behind the gunner, and had only one periscope for vision. This meant that he had a hard time surveilling the battlefield and searching for targets for the gunner. His reliance on the intercom and radio with other tanks must have been increased.

Cutout view of the first K-91, with view of the armor thickness, suspension, engine and transmission, crew and ammunition. Note the cutout in the armor and bulge for the loader’s head to fit.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 34

On the front right side of the gun sat the driver, who had a pivoting driving system. This allowed the turret to turn freely, while the driver would still be in the same position. It is unclear if the turret would have been able to complete a full 360° turn with this system. The driver did have two pericopes for vision (one could be the loader’s, it is hard to tell from the drawings). The loader sat behind the driver, slightly more towards the center, with full access to the gun breach. He had the not-so-easy task of maneuvering the large 100 mm rounds through the very low roof of the turret. The ammunition was placed all around the rear of the turret and inside the turret ring. As proof that even the designers found the turret roof to be too low, they had to make a cutout and slight bulge in the armor so that the head of the loader would actually fit. To put it into perspective, the average tanker was between 160 to 170 cm in height.

Armament

The main gun was to be a 100 mm D-46T. This was a brand new gun developed by OKB No.9 as a replacement to the D-10T. The project was greenlit on 21st May, 1948 and two were produced in Factory No.9 in 1949. It was, however, most likely canceled and used for the development of the D-54. The shells weighed between 16 and 17 kg and would have a muzzle velocity of 1,000 m/s. The gun had +20° of elevation and -3° of depression.

Top cutout view of the first K-91 variant. Here, the internals can be easily seen, such as the crew positions, transmission, fuel tanks and cooling.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 34

The secondary armament consisted of two 12.7 mm DShK heavy machine guns. One was mounted coaxially, on the right side of the gun. This does raise questions of who could have loaded it and cleared jams. The driver was the only one that could realistically reach it, but that involved the driver not driving the tank. The loader would have been required to almost lay over the gun to reach the machine gun. The roof-mounted DHsK was mounted on a rotating pintle, similar to the IS-3 and IS-4 heavy tanks. The loader or commander could have fired it.

Propulsion

To decrease the height of the hull as much as possible, a boxer engine was used. Boxer engines have the cylinders arranged horizontally, facing away from each other. This allows for much lower engines, but considerably wider, compared to straight-heads or V-shaped ones. Additionally, boxer engines offer finer and more responsive performances, but are more expensive to build. The engine was most likely a V-64 12-cylinder diesel, outputting circa 700 to 800 horsepower. On this variant, the engine was placed in the rear, behind the turret, while the gearbox and transmission were in the front, where the drive wheels were also located. To transmit the power, a large shaft ran through the entire length of the vehicle, in between the torsion bars and turret ring floor. There were two fuel tanks, one underneath each cheek of the turret.

Suspension

The suspension of the K-91 was very unusual. It had 9 roadwheels per side, attached with suspension arms to torsion bars. The first three arms were facing the opposite from the last 4. The first and last 2 wheels were sprung by just one torsion bar and attached via a pivoting bogie. The idler was the same as the road wheels, while the sprocket was very large to allow for good crossing of obstacles. The suspension seems to have had very little space in which the wheels could move, meaning either that it had to be quite hard or that the wheels would easily hit the bump stops and transfer the rest of the shock to the hull.

Cutout frontal view and normal view. Note the complex armor of the turret with the bulges, and the wide boxer engine.
Source: Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 34

Armor

As expected, the K-91 was very well protected, with around 200 mm of armor on the upper frontal plate, angled at 45°. The lower frontal plate was around 150 mm angled at 50°. The frontal cheeks were vertical but angled outward from a frontal viewpoint. They were 150 mm thick, and so was the side armor, which was completely flat. Rear armor seems to have been two angled 75 or 100 mm plates.

The turret was extremely complex in its design. It appears to have been cast, with several uneven bulges for the crew. It was 200 mm thick at the base and got exponentially thinner as the angling got higher. The bulges remained 200 mm thick, as they were less angled.

It is hard to tell if the vehicle remained under the 50-tonne threshold, but considering its small profile and smaller gun (compared to most Soviet heavy tanks), it could have reached 45+ tonnes.

Other variants

Kravtsev’s bureau designed two more vehicles as the K-91; a self-propelled gun version based on this variant and a heavy autoloading tank with a rear mounted turret.

The K-91 heavy tank with an autoloader and rear mounted turret.
K-91 SPG, based on the chassis of the first K-91 heavy tank.
Source:Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965, page 35

The video game company Wargaming has made a fake hybrid of this variant and the rear-mounted variant, taking the turret and putting it in the back, for their video game World of Tanks.

Conclusion

None of the three K-91 vehicles designed at OKB IC SV got far due to the apparent lack of improvement over contemporary heavy and medium tanks. The vehicles were quite complex and expensive from a design viewpoint but were fundamentally crude and rudimentary. The designs were terminated in late 1949. Kravtev’s bureau went back to designing APCs and light tanks and developed the K-78, K-90 and K-61, among others.

Front-mounted K-91 variant in a fictional livery.

K-91 (front turret) specifications

Dimensions (L-W-H) 10.230 (6.300 w/o barrel) – 3.340 – 2.150
Total Weight circa 49 tonnes
Crew 4- commander, gunner, driver, loader
Propulsion V-64 boxer 12-cylinder diesel, est. 700-800 hp
Speed N/A
Armament 1x 100 mm D-46T
1x co-axial 12.7mm DShK
1x AA 12.7 mm DShK
Armor 200 mm around turret
200 mm UFP
150 mm LFP, cheeks, side
Total Production blueprints only

Sources

Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965
Yuri Pasholok on the Soviet STG – Status Report (ritastatusreport.live)
https://military.wikireading.ru/56371

Categories
Cold War Soviet Prototypes

Gremyakin’s Medium Tank (STG)

Soviet Medium tank (1953) – Blueprints only

The STG was a tank designed by Soviet engineer Gremyakin around 1952 to 1953. It came as a proposal to the Ministry of Defence of the USSR, which wanted a new medium tank, but with the armor and firepower of a heavy tank, and with the dimensions and mobility of a medium tank. Gremyakin’s proposal did not get far, and it is likely that it was never given any official name, with no names in the blueprints, which are all that remains. It is now commonly known as the STG (Abbrev. of romanized Russian, Sredniy Tank Gremyakin, Eng: Gremyakin’s Medium Tank).

History

On 20th May 1952, the Defence Ministry of the USSR held a meeting with the heads of the largest tank plants and the Marshal of Armored Forces, Semyon I. Bogdanov, on the topic of modernization and development of new tank projects. Shortly after, on 18th June, the decision to develop a new medium tank was made. The chairman at the GABTU (Main Directorate of Armored Forces), V.V. Orlovsky, held a meeting with N.A. Kucherenko, who was part of the leadership of the tank production department of the Ministry of Transport Engineering of the USSR, and sent the requirements to several factories, including:

  • Plant No.75 (Malyashev Factory), Kharkiv
  • Plant No. 174 (Lenin Factory), Omsk
  • Plant No. 183
  • VNII-100 (research institute of Kirov Plant), Leningrad

It was meant to be superior to the T-54 in most categories, from firepower to range, to armor and speed. The T-54 itself was equipped with a 100 mm D-10T gun, very competent for the time. Armor was between 100 mm and 120 mm on the front hull (depending on the production model). The engine was a 520 hp ‘V-54’ water-cooled diesel engine.

Armor profile of T-54A, which also appeared in 1953. It was greatly inferior to that of Gremyakin’s tank, while still a larger tank.
Source: M.V. Pavlov, I.V. Pavlov. Domestic armored vehicles 1945-1965

The requirements were to be:

  • Mass of 34 tonnes
  • Initially, 100 mm or 122 mm gun, later on, a 100 mm D-54 rifle gun with 50 rounds of ammunition
  • Width of 3,300 mm and height no more than that of T-54
  • Ground clearance of 425 mm
  • 3 x machine guns: 2 x 7.62 mm and a single 14.5 mm AA
  • Maximum speed of at least 55 km/h
  • Off-road speed between 35 to 40 km/h
  • Power/weight ratio of 20 hp/tonne
  • Range 350 km

Several proposals were presented, one of the most popular being the Object 907 medium tank, which featured an unusual flying-saucer-shaped hull.

Gremyakin presented his blueprints in June 1953. He was a qualified engineer considering the detail and quality of the blueprints and might have worked for Factory No.75, which had previously made several rear turreted medium tanks, like the Object 416, or the Chelyabinsk tractor plant, which also had experience with rear-mounted turrets.

Layout & Design

Gremyakin’s surviving blueprints show a low silhouette tank with a large, rear-mounted turret. The engine and transmission were mounted in the front, driving front-mounted sprockets. Both the front hull and front of the turret were very thickly armored but got progressively thinner towards the roof. The side and rear armor, however, was still very thick, especially in proportion to the front.

Surviving blueprints of the side of Gremyakin’s tank. Note the in-arm external suspension.
Source: Alex Tarasov

To keep height and weight down, the designer opted for some interesting solutions. Firstly, the use of externally mounted suspension, using a drum-shaped spring, freeing up internal space. The rest of the tank design was also extremely slim. The hull was only as tall as the engine required, and the turret, in typical Soviet fashion, only allowed for a couple of degrees of gun depression, since the turret roof was so low. Otherwise, the running gear and tracks were the same as those of other contemporary heavy tanks.

Placing the turret to the rear allowed for a shorter barrel overhang and better weight distribution. However, it created a host of other problems. The most obvious one was the driver’s placement in the turret, creating an awkward driving position, further cramping up the turret, and creating a hazard when escaping the tank in an emergency. Additional problems, like sight distortion caused by engine and exhaust heat and barrel damage from the engine cooling/intake, might also have been serious, but which can only be confirmed and addressed when reaching a working prototype stage – which Gremyakin’s invention, and many others alike, never reached.

The unusually small size of the tank was to be praised, considering it was well armored and had mounted a large caliber gun. Total height was 2,140 cm, length was 6,700 cm (excluding barrel), and 9,085 cm including the barrel.

Gremyakin’s tank compared to the T-54 and T-10:

Armament

The gun shown in the blueprints was actually a D-25T 122 mm gun. This could easily have been replaced by the 100 mm D-54 or 122 mm M-62, as found on the T-10. It is important to highlight this, as the tank was meant to provide heavy tank-like firepower. The D-25T was the same gun as on the IS-2 and many other WWII-era Soviet vehicles, rendering it obsolete for 1953. This suggests it was added as a placeholder for another gun, suiting the competition. Its ammunition was two-part, stored in the turret. The projectiles themselves were stored alongside the turret wall, starting from the side of the driver, all the way around to the commander. The shell cases were placed in front, and started from the gunner, and ended at the loader. This suggests that there was some kind of moving system for the shells to make them accessible.

As secondary armament, it seems like the tank had one co-axially mounted 14.7 mm KPV heavy machine gun, probably loaded by the loader, but operated by the gunner. It is also possible that an external roof-mounted machine gun could be mounted, on a pintle, perhaps a 12.7 mm DShK.

Previously unseen plans of Gremyakin’s design, showing it from the top. Note the angling of the hull towards the edges and hatches.
Source: Alex Tarasov

Crew

The tank had a crew of 4: commander, gunner, loader, and driver. They were all located in the large turret, encircled by the ammunition.

The gunner sat to the left of the gun, on a seat attached to the turret, from where he could aim and fire the gun, plus use the standard turret controls. Besides the main gun sight, he also had a rotating sight above him for vision. The blueprints do not show a hatch for the gunner.

The tank commander sat right behind the gunner. He had 3 or 4 periscopes for vision and also (probably) controlled the radio.

The loader sat on the right side of the gun, loading with his left (usual in Soviet tanks). He had the excruciating job of handling the large ammunition within the very tight space. Thankfully, a loading tray was given, so that he could rest the round on it. Unlike the rest of the crew members, he was faced directly towards the gun. He had one entry/exit hatch with a rotating periscope. There was another hatch behind him, probably for easier access when reloading the tank with ammunition. The loader was probably also tasked with loading the coaxial machine gun, however, it must have been near to impossible due to the driver being in the way. This does raise the possibility the driver would reload the machine gun or some other kind of innovative system.

The driver’s position, however, is the most interesting. Located in the turret, in front of the loader, he was in what appears to be a rotating device on its own axis, independent of that of the turret, yet still spinning along with the rest of the turret, consequentially meaning that the turret had limited traverse. Of course, this is all speculation. He appears to have a rotating device instead of the traditional tillers or steering wheel.

Top view of the turret, essentially the entire crew compartment. Note how the crew is encircled by ammunition, however considering the turret’s very thick armor, it is not as bad as it might originally seem.
Source: Alex Tarasov

Armor

For a medium tank, Gremyakin’s design was unrealistically well protected. The thickest part of the frontal hull plate was around 320 mm thick. Likewise, the base of the turret was a whopping 355 mm thick, gradually getting thinner as it rounded upwards, to around 60 mm at the roof. It gradually got thicker again towards the rear of the turret, with 280 mm of armor at the base. Even the rear hull armor was, at the thickest, 140 mm angled at 60°, for a total effectiveness of 150 mm. The thinnest part of the tank was the hull belly armor, at 25 mm.

This sort of protection was far superior to contemporary heavy tanks. The T-10 had 120 mm at the front. This begs the question if the tank could even remain around the 34 tonnes area. It was larger than the T-54 (apart from being slightly lower), but with significantly more armor in raw thickness alone.

Engine

The engine was of an unknown type, but to reach the desired 20 hp/tonne, it needed around 680 hp. This would point to the V-12-5 engine used on the T-10. The fuel tank was placed on the other side of the hull, behind the turret.

Suspension

The suspension of the design is very peculiar. Most Soviet tanks used torsion bar suspension, in one form or another. External suspensions were common in pre-war Soviet designs, but their use diminished during the Second World War, both in the Soviet Union, but also in other nations. Gremyakin most likely used external suspension to lower the height of the vehicle and improve maintenance and replacement of the suspension, one of the main drawbacks of torsion bar suspension. Yet what exact system he used is unknown. Externally, it looks like hydropneumatic suspension, similar to that used on some modern main battle tanks. But using hydraulics does not make much sense, and the Soviet Union would not use hydropneumatic suspensions on tanks until the 1960s in tanks like the Object 911 and Object 911B. The only such systems used in the 1950s were on the BRDM-1 and 2 armored cars.

The rounded shape of the suspension indicates to a very unique suspension system; torsion springs. These were used on some Italian tanks and armored fighting vehicles. It consisted of a flattened coil, but instead of mounting it vertically, it was mounted inwards. The movement and tension would not be exerted by compression, but by torque. The most basic use of such springs today is in clothespins.

Torsion springs used on the Italian CV38.
Source: Unknown

Fate: Failure

Considering that it never even got a proper name, Gremyakin’s design never got very far. It was plagued from the start by cramping heavy tank armor and guns into a medium tank. Terrible crew ergonomics and little gun mobility were also compromises Soviet tank designers often took in order to keep height and weight down.

The largest drawback of Gremyakin’s design was ambition. The tank had so many innovative and challenging characteristics.

First was placing the driver inside the turret. This presented a very complex and expensive system, cramping the turret. In addition, it would give a very awkward driving position and compromise turret rotation. It was not a new concept, tanks like the Object 416 used it previously, but with little success.

Secondly, all the features and gadgets on the tank would increase its cost of production, maintenance and complexity. An ammunition pushing system, completely unique suspension to name a few.

Lastly, and most importantly, the armor of the design was, to say the least, excessive. While there is nothing unusual with thick angled armor, it was surely ambitious for a medium tank program with a 34 tonne weight threshold. This would have significantly increased the weight from a vehicle of the weight of the T-54 more to that of the T-10. To maintain its 20 hp per tonne power to weight ratio, it would have required a much larger, more expensive engine.

Other designs were selected for trials, like the Object 907 medium tank from VNII-100. However, none of these tanks offered a substantial improvement over either the T-10 and T-54 tanks. Both of those tanks were already in service and were excellent at what they were designed for, not allowing any room for a very expensive medium-heavy hybrid.

Plans of the Object 907 medium tank, also designed as a medium tank with heavy tank armament and armor. Despite complicated hull shape and extreme angles it did not offer a huge advantage over existing tanks.
Source: M.V. Pavlov, I.V. Pavlov. Domestic armoured vehicles 1945-1965
Illustration of the Gremyakin medium tank (STG) by Pavel Alexe, funded through our Patreon campaign.

Sources

TsAMO state archives
Опытный средний танк “Объект 907” (topwar.ru)
M.V. Pavlov, I.V. Pavlov. Domestic armored vehicles 1945-1965
С боевым отделением в корме: yuripasholok — LiveJournal

STG specifications

Dimensions (L-W-H) ≈ 5 x ≈ 3.5 x ≈ 2 m (excluding barrel)
Total Weight, Battle Ready ≥34 tonnes
Crew 4: Commander, Gunner, Loader, Driver
Propulsion ≈ 680 hp, possibly V-12-5
Speed ≈ 35 – 55 km/h
Armament 1x 122 mm D-25T or 122 mm M-62
Coaxial 14.7mm KPV heavy machine gun
Potential roof-mounted 12.7 mm DShk heavy machine gun
Armor Approx:
Front: 200 mm
Side: 100 mm
Rear: 100 – 120 mm