Categories
WW2 Soviet Prototypes

GAZ-68 / KSP-76

Soviet Union (1943-1944)
Experimental wheeled infantry support gun (1 built)

The SU-76 remains, to this day, one of the most well-known Soviet self-propelled guns of the Second World War. Yet, at the start of its production, it was plagued by unreliability and mechanical issues caused by its drivetrain. Thus, production was halted at only 560 units in order to remedy these problems. Solutions came with the SU-76M in 1943, but in between this period, another vehicle was designed, not to replace the SU-76, but rather supplement it. This was the GAZ-68 (also later referred to as KSP-76). Meant as a desperate and ultimately unsuccessful attempt to bolster tactical mobility, it was meant to provide close support artillery for rifle and cavalry units through direct fire. The GAZ-68 was based on a truck chassis, and the main gun would still be the famous ZiS-3 field gun.

SU-76M in what seems like Berlin, 1945. The SU-76M was an attempt to fix some problems with the SU-76. The GAZ-68 was a different vehicle in its role but would have functioned alongside the SU-76s.
Source: Pinterest

Why?

Throughout the early stages of the Second World War, the Soviet military found itself in a dire need of a fast vehicle, with good firepower, able to take on German Panzers but also other targets. Mainly, it would assist the infantry units in dealing with armored and unarmored targets, but also have the capability of responding quickly, moving and penetrating deep into enemy lines, accompanied by infantry attacks. Until 1943 and ‘44, the RKKA had no designated infantry support vehicle, relying entirely on towed artillery. Using a wheeled chassis as a basis, would allow much greater on-road speed, while also, theoretically, keeping production and maintenance costs down. On paper, a vehicle like the GAZ-68 was just what the Red Army needed, but in reality, it was the complete opposite, a consequence of the Soviet war and industrial struggle. Contrary to popular conceptions, this vehicle was not meant for artillery units for indirect fire or ‘shoot and scoot’ purposes, rather just an infantry support gun.

Front of the GAZ-68 as it is preserved at Kubinka, Moscow.
Source: A. Tarasov’s personal collection

Development

Shortly after the battle of Kursk (July – August 1943), where the use of mobile defenses and counter-attacks (plus numerical superiority) proved key for the Soviet victory, the mobility of artillery and self-propelled guns proved crucial. Thus, the Gorky Automobile Plant (Gorkovsky Avtomobilny Zavod, GAZ) started the development of a wheeled infantry support gun with the approval of the head of GAZ, V.A. Grachev, who was head designer of the project, while N. Astrov was head of the project. Already in August of 1943, the design office and plant management approved the idea. Grachev, a lesser-known name within western literature, was the chief designer at GAZ between 1941 and 1944 when he created many vehicles, most notably the GAZ-64 and BA-64. Post-war, he continued his career at ZiL, where he created, among others, the famous ZiL-157 and BTR-152.

The first ideas involved mounting a ZiS-3 gun on a 1½ tonne truck chassis, with only minor modifications. Clearly, the main goal here was to get a mobile vehicle for as little money as humanly possible.

Drawings for the installation of a ZiS-3 76 mm gun on a truck chassis, which has been stripped down to the bare minimum, missing even an enclosed driving cabin. For obvious reasons, the combat value of such a creation would be extremely limited.
Source: Солянкин А.Г., Павлов М.В., Павлов И.В., Желтов И.Т. Отечественные бронированные машины. XX век. Том 2. 1941-1945

The idea of a wheeled infantry support gun interested the Soviet military, leading to a go-ahead to the project from the People’s Commissariat (Ministry) of Medium Machine Building and the Main Armored Directorate of the Red Army (GABTU). Previously, all self-propelled artillery projects were under the command of GAU (Main Artillery Directorate), until all the SPGs were re-subordinated to GABTU as Stalin personally was outraged that the GAU adopted SU-12 (SU-76) in an unsatisfactory condition. Thus, the Directorate of the Self-Propelled Artillery of the GABTU was established on the 21st of May 1943.

Work started in October of 1943 under the name ‘Izdelie 68-SU’, but this was changed to GAZ-68. By December, a wooden mockup was already completed and documentation on the vehicle from GAZ was sent to the GABTU in mid-December. The GABTU approved the project for further development. On the 7th of February, 1944, the GABTU gave a green light for the production of a prototype. It was around this time that the name ‘KSP-76’ appeared, most likely a product from GABTU to remove the GAZ factory name. It stands for Wheeled Self-Propelled Gun with a 76 mm gun (‘Kolyosnaya Samokhodnaya Pushka’, KSP).

An experimental model of the wheeled self-propelled gun KPS-76.
Curiously that the name in the document is КПС-76 (KPS-76), not KSP-76.
Source: TsAMO

Following the approval for a prototype, the design bureau quickly sent the plans and documents to the workshops, which meant that, by April, the armored hull was completed. This was designed by Y. N. Sorochkin and A. N. Kirilov and was to protect from small arms fire and splinters. To keep weight down, the top was left open. On the 4th of May, the prototype was already completed.

An important part of this quick development and production process was the use of an already tried and tested chassis (not that this meant much for the Soviets, as there were plenty of prototypes in all fields made pre-war, but in this case, it did help boost development). The GAZ-68 was based on the GAZ-63 truck, however, it needs to be pointed out that the production of the GAZ-63 began only in 1948. Rather, the GAZ-68 was based on the experimental GAZ-63 developed in 1939. Essentially this was an all-wheel-drive GAZ-51, which itself was made to replace the aging GAZ-MM. Ironically, a GAZ-MM superstructure was used for the prototype. A Dodge D5 Diesel engine was used, outputting 76 horsepower, coupled to a 4-speed transmission. These trucks were tested at Kubinka in 1940, with good results. Mass production was to begin in 1942, but the start of the Great Patriotic War (as WW2 is called in Russia) meant that all projects were canceled.

The GAZ-63 model 1939. Not to be confused with the GAZ-63 model 1948.
Source: Rus-texnika.ru

Grachev, very sensibly so, claimed that using this already finished and tested chassis would greatly increase the development speed and trials. The advantages of a wheeled vehicle over a tracked one are also clear, with cheaper maintenance and higher speeds on roads. The designers wanted to use as many readily available components as possible for reliability and production purposes. This idea was, however, the one that led to the GAZ-68’s demise.

Design

The GAZ-68 was surely an unorthodox vehicle, especially by Soviet standards. However, at its core, it was essentially a SU-76 on wheels, albeit 69 cm narrower, 65 cm lower, and 135 cm longer.

The superstructure was thinly armored, made from a simple box, and no roof. The gun was mounted slightly behind the front wheel axle. The driver was located to the right of the gun, and with the gunner to the left. Ammunition was stowed to the sides of the casemate and behind. Thanks to the long wheelbase, the vehicle was very low to the ground, ideal for ambushes and camouflage, but also offered good stability. The engine was located at the back, over the rear axles. The design was rudimentary and simple, allowing for a very cheap vehicle to manufacture if the situation of Soviet truck plants was not as disastrous as it was. The top could be covered with a tarpaulin to protect from precipitation and wind. Two large fenders would protect the front wheels. As a result of the lack of resources, automotive plants were forced to take shortcuts during production, such as fitting just a single headlamp. On the GAZ-68 it was placed on the left side fender, to not further impair the view of the driver. Coupled with the low-mounted gun, these give the GAZ-68 its iconic look.

The very low profile of the GAZ-68/KSP-76 can be seen here. It was only 155 cm tall, 54 cm shorter than the SU-76. This would have made it a smaller target, crucial for a vehicle with such little armor.
Source: Maximonline.ru

Crew

The vehicle had a crew of only 3, a gunner (who also served as a commander and radio operator), a driver, and a loader. The gunner was responsible for aiming and firing the main gun. He had two vision slits through which he could see, plus the scope of the ZiS-3 gun, extending above the frontal shield. If in doubt, he could just stick his head up to get a clear 360° view using a pair of binoculars. The gunner also had a panoramic sight at his disposal.

Overloading the gunner/commander with so many tasks is unusual for the Soviets, especially in a late 1943 design and it is noteworthy that there was also enough space in the vehicle to put a fourth crew member, although test reports claim other crew positions were cramped. It is also worth mentioning that the Soviets had already suffered catastrophic losses, especially in specialized troops, such as tankmen. This might have been a deciding factor.

Commander/Gunner’s location. Radio and equipment have been removed, but the sight is still there.
Source: svsm.org

As mentioned previously, the driver sat on the right. He had a slightly larger viewport to view out of compared to that of the commander. Oddly, the large steering wheel went above the viewport, which could have been inconvenient for taller drivers.

Driver’s position. Most of the electronics and dials have been removed, but there probably were not many to begin with. Note the large viewport.
Source: svsm.org

The loader was seated behind the gunner, on a foldable seat. He had a ready rack behind him, incorporated into the engine compartment and in front of the fuel tank, which was not very safe, but considering the overall protection, or lack thereof, it did not matter. Forty-one rounds were stored here, in a horizontal position. 13 more rounds were stored on the other side, vertically, behind the driver. The crew also had 2 PPSh submachine guns for self-defense, with 12 magazines (852 rounds).

View from the front of the rear of the fighting compartment. Note the foldable loader’s chair on the right. The rack is right behind him, but is, in this picture, almost obscured by the cover. On the left, the other rack can be seen, and other storage spots.
Source: svsm.org

Armament

The armament of the GAZ-68 was the trusty 76 mm M1942 ZiS-3 divisional gun, one of the most common guns within the Red Army at the time, and also the main weapon of the SU-76. The field gun was capable of both direct and indirect fire (once mounted on the GAZ-68 it was not). Over 100,000 units were produced by the end of the war and saw service post-war with many nations. It had a range of above 10 km and could use a variety of shells.

The KSP-76 would have most likely used AP and HE shells, but there were AP, APHE, HE, HEAT, Fragmentation, and other shells available. Most shells weighed around 6 kg and had a muzzle velocity between 680 and 700 m/s. On the KSP-76, 54 rounds were stored in total. The position of the gun in such a low profile vehicle affected its ergonomics compared to a regular field gun mount. The gun could only be elevated to +15° and depressed to -3° and had a horizontal traverse of 37°, 18.5° to both left and right sides of the gun.

The gun was supported by a travel lock mounted on the edge of the frontal slope. Despite the rather large compartment, the estimated rate of fire was 8 rounds per minute (one round in 7.5 seconds). The ergonomically well-placed ammo rack could have allowed an experienced loader to shorten the reload time even more.

The vehicle lacked any secondary armament, which was a common defect in Soviet SPGs, making them extremely vulnerable in close range combat with infantry, exactly the type of engagements the KSP-76 was meant to tackle.

View of the vertical breech and aiming system to the left.
Source: svsm.org
The iconic recoil system of the ZiS-3 mounted on the KSP-76.
Source: svsm.org

Armor

The armor of the vehicle was thin, only being able to withstand rifle fire and shrapnel. The GAZ-68 was never meant to be well armored in order to keep costs and weight down, plus its low silhouette would have played a big role in improving its survivability. The frontal plate was initially 10 mm thick, later increased to 16 mm. The top of the sides was 7 mm and the inwards angled bottom side plates 4 mm. This was not even bulletproof but would provide some protection against shell splinters and ricochets. The roof of the engine compartment was 5 mm thick but there was no protection over the heads of the crew apart from their own helmets leaving them, and some of the ammunition dangerously exposed. The cutting of corners and economy made in this aspect of the vehicle made it have a low unit production cost but would have clearly made it vulnerable to even rifle rounds from the side. The tires were bulletproof, filled with an elastic substance.

External view of the front corner, driver’s side. Note the thinness of the welded front and side plates. There were small covers for the viewports, but these seem to have vanished.
Source: svsm.org

Engine and Chassis

The chassis was, as previously stated, that of the GAZ-63 model 1939 truck. The engine and transmission were changed from the truck to a single GAZ-202 (some sources state that the engine was a GAZ-202, but the TsAMO document states that it was a GAZ-203), engine outputting 85 hp, mounted in the rear compartment, offset by 276 mm to the right. To the left of the gun, a 140 liter insulated fuel tank was placed. In front of this, the 41 round ammo rack was placed. A very scary thought, considering the armor was only a few millimeters thick! An upwards-facing cooling grille was placed in the back. The transmission was a 5-speed manual (4 forwards, 1 reverse) coupled to both axles. However, the rear axles could be disconnected from the drive when not needed such as on a long road march. The suspension was standard and common to the truck consisted of simple leaf springs and shock absorbers.

Rear top view of the prototype. The rear compartment housed the engine, transmission, fuel tank, and ammunition, with only 4-7 millimeters of protection.
Source: Topwar.ru

Trials and Fate

As soon as the prototype was finished, it began factory testing around May 1944 and had finished tests by autumn of the same year. From the Gorky factory, the GAZ-68 went to the Kubinka test range. Allegedly, it traveled under its own power and with an impressive speed of 60 km/h. Again, this information has to be taken with a grain of salt.

In September-December 1944 the experimental SPG was tested at Kubinka proving grounds and Gorokhovetskii artillery range. During a 2,528 km test drive, it is claimed to have reached a top speed of 77 km/h on-road, but this seems hardly possible in regular conditions. Even if it was true, the limited view of the driver would make such a speed hazardous, to say the least. The vehicle only had an 85 horsepower engine and weighed 5,430 kg battle-ready. During firing trials, 409 shots were fired of unspecified type at the Gorokhovetskii artillery range.

However, testing was not all going to plan for the Soviets. The original chassis took a hard beating and broke down frequently, putting into question the validity of the tests made at Kubinka of the GAZ-63. The driveshafts, gearbox, leaf springs, and frontal axle suffered some form of damage. To be fair, the GAZ-68 did weigh over 2 tonnes more, with different weight distribution. It was also noted that the crew compartment was too small and uncomfortable for some of the crew, especially the driver, who was cramped up by the gun and steering wheel.

The small silhouette and profile of the vehicle were deemed as a plus. However, there were significant issues with accuracy, thanks to the chassis and the suspension, which made the ride very bouncy. This also caused the sight and barrel to become misaligned after driving. Off-road tests were a mixed bag. On one hand, the GAZ-68 proved satisfactory, on the other, it was far inferior to what a tracked vehicle was capable of. Testing was finished by the 24th of December. The Military Council of the Armored and Mechanized forces of the Red Army (Военный Совет БТ и МВ КА, Voennii Sovet Bronetankovyh i Mekhanizirovannyh Voisk Krasnoi Armii), proposed to GOKO (State Committee on Defence) to produce the initial test batch of 10 units at the GAZ factory and undergo army tests. However, this was not achieved and, instead, the project was terminated altogether.

The situation of the war in mid-1944 was very different than that of a year earlier. The Red Army had been on the offensive for almost a year, pushing the Axis almost back to the pre-war borders, and the Allies had just landed in Normandy, sealing the fate of the war. The implementation of the GAZ-68 made even less sense now than it did before, and the questionable combat value it would have brought would far outweigh the industrial strain, despite the seemingly cheap production price.

Doomed from the start

Even before starting prototype production, the fate of the GAZ-68 was predetermined. The straightforward fact that it was based on a truck chassis, which for the designers certainly seemed like an advantage, but the industrial capabilities and resources of the USSR could not deliver. The Soviet industry could not keep up production of ZiS-5 and GAZ-AA simple flatbed trucks, even with help through the Lend-Lease program, let alone the mass-production of an even more complicated truck designed in 1939 and canceled because of the German invasion.

Automotive factories could not start assembly of a new, complex, and relatively new design, in the conditions that they could not even keep up with simple production models. It is important to note, both of these truck models were standard commercial trucks, with little to no improvements for off-roading or any sort of military specialization. Before the war, the Red Army only had the GAZ-M1 and no off-road trucks.

Side view of the prototype showing off the impressively low profile to a good extent. Note the tarpaulin and muzzle cleaning rod.
Source: Topwar.ru

The GAZ-68/KSP-76 was also doomed through its design. The use of wheels would have given it faster speeds on good terrain, but most of the western Russian terrain was flat plains and forest, with poor road connections. This is not to take into account the harsh conditions of thick winter snow or deep muds, where even tracked vehicles could struggle. The supply of tires before and during the war was also a big issue for the Red Army. While the situation to some extent improved during the war, they still relied on imported tires for around 33% of their needs.

In modern eyes, a wheeled vehicle might seem superior, as we now have many roads and good infrastructure, plus more advanced technologies, but this was Russia in 1943. The GAZ-68 was simply not compatible with Soviet military doctrine, industrial capabilities, and the terrain of Eastern Europe.

Compared to the SU-76, the GAZ-68 was far cheaper to build and maintain, was 54 cm lower, but with similar protection levels and firepower, in addition to the pros and cons of a wheeled chassis. Whether the KSP-76 was an improvement over the SU-76 is up to debate, but it clearly was not enough to justify the changing of truck production lines to a new vehicle this late into the war.

GAZ-68/KSP-76 illustrated by Pavel Alexe, funded through our Patreon Campaign

GAZ-68 / KSP-76 specifications (Source: TsAMO)

Dimensions (L-W-H) mm 6,350 / 2,050 / 1,550
Total Weight, Battle Ready 5.39 tonnes
Crew 3 (Commander, Driver and loader)
Propulsion X
Speed X km/h
Range X km
Armament 76 mm gun ZiS-3 M1942 Regimental gun (662 m/s muzzle velocity)
Ammunition count 54
Maximum speed, km/h 62.5
Average speed on a paved road, km/h 49.3
Average speed on an unpaved road, km/h 21.2
Engine GAZ-203 (with an aluminum head) outputting 85 hp
Fuel type and range KB-70 or B-70 fuel,
140 liters for 430 km range
Armor (frontal hull, fighting compartment), 7-16 mm
(Sides, rear hull and fighting compartment), 4-7 mm
Total Production 1 prototype

Sources:

https://topwar.ru/51030-kolesnaya-sau-gaz-68-ksp-76.html
S. Lopovok, Inventor and Rationalizer, No 12,
Zaloga, Steven J., James Grandsen Soviet Tanks and Combat Vehicles of World War Two
https://rus-texnika.ru/gaz-62-obrazca-1939-goda.html
A.V. Karpenko. Part 1. Light self-propelled artillery installations  Domestic self-propelled artillery and anti-aircraft installations
https://rus-texnika.ru/gaz-63-obrazca-1939-goda.html
https://tech.wikireading.ru/9308
Солянкин А.Г., Павлов М.В., Павлов И.В., Желтов И.Т. Отечественные бронированные машины. XX век. Том 2. 1941-1945
TsAMO & GABTU archives (from A. Tarasov)

Categories
Cold War Soviet Prototypes WW2 Soviet Prototypes

Object 704

USSR (1945)
Heavy Self-Propelled gun – 1 prototype built

The SU-152 and ISU-152 were, and still are, well known for their massive guns and impressive claimed capabilities against German tanks such as the Tiger and Panther. That is how they got their nickname “Zveroboy”, meaning beast killer. However, that was more related to propaganda than their actual usefulness as tank destroyers. Their massive 152 mm guns, while very effective if they hit the target, were rather inaccurate at long range, slow to aim and to reload, and limited in traverse by their mounting in a superstructure. These guns were not well suited for a tank destroyer. The SU-152 and ISU-152 were not, in fact, tank destroyers, but assault guns, meant to help Soviet attacks break down enemy defenses and strongpoints. Yet, for assault guns, their protection was more often than not, quite lacking. With the start of production of the Kirovets-1 (Object 703, or better known as IS-3), the opportunity arose to improve the “Beast Killers”, now focusing on protection. This vehicle was to become the Object 704 or Kirovets-2. It is also called ISU-152 model 1945 in Russian literature, however, it is likely that the Object 704 was never referred to as such in the short life it had, and could be a modern name, possibly invented at Kubinka, according to Russian historian Yuri Pasholok.

Despite the success of the ISU-152, its weak armor, tall silhouette, and inconvenient muzzle blast made the Soviets seek a replacement. Ironically, they never got one and the ISU-152 served decades after WWII. Source: Pinterest

Development

Due to the problems of the ISU-152, proposals came as early as 1944 from GABTU (Main Directorate of Armed forces) to the SKB-2 plant to upgrade the vehicle, however, little materialized. Then, work started on a new IS tank- the Kirovets 1 (IS-3).

There were also plans to modernize the gun on the ISU-152 as well. In 1943, the GABTU Artillery section stated that the 152.4 mm ML-20S howitzer was not suited for use on a self-propelled gun. The issues on the ML-20 naturally reflected on the battle performance of the ISU-152. An example was the TsAKB slotted muzzle brake kicking up a lot of dust, almost blinding the gunner after firing, and more importantly, revealing the vehicle’s position.

Thus, the GABTU put out a series of requirements for the modernization of the weapon. Firstly, this included the removal of the muzzle brake, changes to the breech, and improvements to the recoil system. OKB-172 was assigned to develop the upgrade by the 13th of January, 1944, headed by M. Tsirulnikov. The new gun was to be named ML-20SM, M standing for modernized. Blueprints were ready by the 1st of March of the same year and, by the 10th of March, the prototype was built in Factory No.172. The very next day, firing trials were undertaken, but after the 33rd shot, testing was halted due to poor operation of the new breech. Further tests were made through March until the 14th of April when it passed the test for rapid consecutive firing of 60 shots, which it fired in 39 minutes. While that might seem like a lot, the initial firing time estimation for them was 60 minutes (1 round per minute), the gun averaging 1.5 rounds per minute. Testing continued into May, the gun firing a total of 249 rounds, out of which 196 were with high explosive charges (for direct firing). The average rate of fire over the entire testing period was an impressive 2.9 rounds per minute. Factory testing of this gun continued until September 1944. Due to the high rate of fire and no muzzle brake, it was decided on the 2nd of October to mount the gun inside an ISU-152. Consequently, the gun was shipped off to Chelyabinsk, but, when it arrived in the middle of October 1944, it was unfinished! At the end of 1944, the GABTU stated that the gun needed urgent work and that factory No.172 workers should be sent to ChKZ. This only happened by mid-February 1945, when the battlefield was different and the IS-3 was approaching mass production, making the ISU-152 chassis archaic.

The massive muzzle blast made concealing the vehicle virtually impossible after firing. It also blinded the crew, so following the shot and keeping track of the target was a challenge. Source: Weapons of Victory

In fact, ChKZ had started working on an SPG based on the Kirovets-1 at the beginning of 1945. It received the name Kirovets-2. The chief engineer and designer was L.S. Trojanov.

A letter from Engineer-Lieutenant Colonel Markin, a representative of the GABTU in ChKZ, was sent to GABTU chief Engineer-Lieutenant Colonel Blagonravov on this topic. It stated that the Kirov factory (SKB-2 to be precise) was working on a Kirovets-1 based SPG, stating its armor thickness level and other features, namely that it used the same transmission, running gear and engine as the Kirovets-1. Most interesting is that, according to the letter, work on the prototype started on the 1st of February, 1945. The letter was sent 10th of February, 1945.

The Kirovets-2, later named Object 704, was an attempt to fix the main issues with the ISU-152, yet created more problems and was plagued by bureaucratic wrangling. Source: Topwar.ru

ChKZ also announced S.P. Gurenko, chief designer of Factory No. 172, saying that SKB-2 was working on such a vehicle. This led to engineers from No. 172 coming over to Chelyabinsk between the 14th and 20th of February. During this time, SKB-2 had sent the blueprints of the Kirovets-2 over to Factory No. 200 as well. Also in mid-February, the hull of the SPG was ready in ChKZ.

On the 3rd of March, a meeting was held on the topic of improving the Kirovets-2. The main issue brought up was fitting the ML-20SM, originally built for the ISU-152, into the Kirovets-2. The gun had been sitting for quite a few months in a hall somewhere in ChKZ. Other points discussed were further increasing the armor and thickening it from 100 to 150 mm (3.9 – 5.9 inches) and replacing the panoramic sight with a Hertz sight from a 76 mm Mod. 1943 ZiS-3 gun, as it was smaller. The telescopic sight was also changed for a smaller TSh-17. The traverse mechanism was altered and, most importantly, it was decided to give the Kirovets-2 a co-axial DShK heavy machine gun, mounted on the right side of the main gun.

The hull of the Kirovets-2 was ready in spring, but the gun was not mounted until halfway through June 1945. This delay was caused by bureaucratic disputes regarding the serial production of the ML-20SM gun. The tank became the Object 704, yet the Kirovets-2 name stuck with factory workers.

Layout and Design

The design of the Kirovets-2 was unique, having little resemblance to previous Soviet heavy SPGs. It still had a frontal mounted casemate, where the turret and pike nose of the IS-3 used to be. Due to the aim to improve the armor protection to the same level as the IS-3, the armor plates were thickened and angled throughout the casemate. On the ISU-152, the gun mantlet was a large frontal weak spot, yet on the Object 704, it was the thickest part of the tank. Interesting to add is that the bottom of the side casemate angled inwards a lot more than it appears to. The almost flat triangle shape part of the side superstructure is actually just a thin sheet of metal.

Although the IS-3 chassis was used, there were still some changes made. Namely, the engine plate was different and the exhaust pipe layout was the same as on the Object 701. It is unclear if this was done to save pieces for the production of the IS-3 or it was intentionally designed as such. An additional small construction detail is the use of several track types, satisfactory for a prototype built in a short period of time. There were 86 tracks per side, each track was 650 mm wide and they were connected by a single pin. The engine was the same V-2-IS engine, producing 520 hp, and the running gear and transmission were kept the same. The transmission was a multi-disc dry friction clutch. The gearbox was a 4+1 dual stage (high/low) manual, for a total of 8 gears forwards and 2 in reverse. The brakes were still planetary rotation mechanisms.

The hull is often said to be identical to that of the IS-3, but the exhausts and engine plate design are different. Note the thinness of the triangular-shaped side plates on the hull can be discerned here. Source: Yuri Pasholok

Despite the external differences, inside, the Object 704 was very similar to the ISU-152. It still had a crew of five; driver, gunner, commander, loader, and breech operator. The heavily angled sidewalls caused major internal ergonomic problems, namely storage for the huge two-part ammunition, which weighed 48.78 kg (107 lb) for the AP and 43.56 kg (96 lb) for the HE, no easy task to load in a tight space. Sacrificing crew comfort and ergonomics for protection was quite common in the late war and post-war Soviet tank doctrine.

Object-704 during testing. The extreme angles of the fighting compartment can be seen. Source: Pinterest

The vehicle’s silhouette was much shorter than that of the ISU-152, now being only 2,240 mm (88 inches) tall, but kept the same width.

Main Armament

The modernized ML-20SM lacked a muzzle brake, which improved the visibility and kicked-up less dust after firing. However, the recoil grew considerably, namely by 900 mm, so a recoil brake was added. The gun had +18° of gun elevation and a shockingly poor -1.45° of depression. The horizontal traverse was not much better at a very limited total of just 11° (5.5° on each side). The new gun fired the same two-part HE weighing 43.56 kg (96 lb) and AP ammunition, weighing 48.78 kg (107 lb), and had very similar ballistics to the standard ML-20S. The HE rounds had a muzzle velocity of 655 m/s, while the AP had 600 m/s. The gun could hit a 2.5 to 3-meter tall target reliably from 800 to 1,000 meters (874 to 1,093 yards), but had a direct fire range of 3.8 km (2.36 miles) and an indirect fire range was 13 km (8 miles).

When conducting indirect firing, the Hertz panoramic scope was taken out through the gunner’s hatch. The practical rate of fire is contradicting and ranges from one to a bit under three rounds a minute. A quick reload was not necessary for such a self-propelled gun, especially considering the terrible ammunition count inside the Kirovets-2; just 20 (19 according to the trial report, although the extra round could be loaded to be 19 +1)) rounds. These were placed on both sidewalls of the fighting compartment, and the charges were placed on the right wall and underneath the breech.

View of the breech of the ML-20SM. Note part of the loader’s tray to the bottom left and the coaxial DShK machine gun to the right of the gun. The manual traverse can also be seen, which was to be operated by the breech operator. Source: Yuri Pasholok

Secondary Armament

The vehicle was equipped with two 12.7 mm DShK heavy machine guns, one coaxially mounted and one on the roof, with 300 spare rounds of ammunition inside (600 according to Kubinka). There was a chute for the ammunition belt to slide over the main gun and into the machine gun.

The roof-mounted DShK was for anti-aircraft use and was mounted on a rotating ring over the loader’s hatch. The ring could swivel over and next to the hatch. The machine gun itself could also pivot on its mount. A collimating K-10T sight was mounted on the gun for easier aiming against aircraft.

For the defense of the 5 crew members, they were equipped with PPSh or PPS submachine guns. Some F-1 grenades could also be mounted on the sidewall, between the commander and breech operator.

Crew

The Object 704 had a crew of 5; driver, commander, gunner, loader, and breech operator. They would communicate with each other with a TPU-4F intercom, having a headset and a microphone. This was essential, as the crew sat quite far away from each other and communication was key in coordinating aiming and directions. Every crew member had his own entry and exit hatch on the roof of the vehicle.

The driver was located higher up in the hull than in the ISU-152, by 600 to 700 mm. Consequently, he did not have his own hatch in the front plate, instead, his vision relied on the single movable MK-4 periscope in his hatch, on the roof. As could be anticipated by such an arrangement, this was not enough, giving the driver rather poor vision when buttoned up. He was, however, also able to open the hatch (by sliding it to the side) and stick his head out in non-lethal environments. To control the tank, he had two mechanical tillers. To his right was the gearshift and the shift for the high/low gear ranges. On a good note, the driver no longer sat next to a large fuel tank, like on the ISU-152, which was good for morale.

The gunner sat behind and to the right of the driver, on a seat attached directly to the gun. There, he had the elevation control hand crank, as well as the trigger, his Hertz panoramic sight, and the 2.5x (other sources claim 4x) magnification TSh-17 sights. This sight was adequate for firing up to 1500 meters (0.93 miles). As previously mentioned, for indirect firing, the gunner’s hatch had to be opened and the sight raised through it. Both sights were illuminated for conducting nocturnal firing. Directly under the breech block was a floor-mounted escape hatch, for a total of six hatches.

The commander was on the opposite side of the driver, also having just one MK-4 periscope for external vision. He was responsible for the radio, placed right in front of him, on the frontal armor plate. This radio was a 10PK-26 radio, connected to the 24 volts onboard power transmitter. The frequency was 3.75 Mhz to 6 Mhz, with a wavelength varying between 50 to 80 meters. While stationary, the range was between 20 to 25 km, and it decreased slightly while on the move. The radio also allowed for communication on two fixed frequencies, simultaneously. The coaxial machine gun was also his responsibility, most likely having to fire it as well. Yet the traverse of the main gun was controlled by the breech operator and elevation by the gunner, so aiming would have been a coordination challenge.

Handling the massive shells was done by the loader. The shells were stacked on the side walls. He was also assigned operation of the anti-air DShK on top of his hatch. To aid him in loading, he had a loading tray, attached to the gun. A round would be rested on it until it was ready to load again. This meant that the loader did not have to hold the round until the breech was open again, a little but crucial detail considering the round’s weight. There were 12 rounds on the wall next to him, while the other 7 were on the other side, by the breech operator, and were a challenge to extract.

Perhaps the most curious crew member position is the breech operator. It is important to note that the breech design was quite ancient and could not open automatically. The breech operator would open the breech while the loader was manhandling the rounds into the gun. Then he would close it. He could assist the loader with charge amounts as well. This was done to decrease the strain on the loader, as it was no easy feat.

While testing reports were quite satisfied with the positions of the crew, a few issues were brought up. The angled sidewalls made storage of ammunition complex and accessing them was cumbersome. Let alone moving them out and into the gun, considering their weight. The elevation of the driver’s position also brought drawbacks, namely, he would bounce around when the tank was moving on poor terrain. This was strenuous on the driver. To boost morale and improve living conditions, two fans were placed behind the gun, to ventilate and remove toxic fumes, as well as a couple of dome lights.

Engine

As aforementioned, the engine was a V-2-IS outputting 520 horsepower. An ST-700 electrical motor, outputting 15 hp (11 kW), was used for starting the main engine. In cold winters, two compressed air cylinders were used to start the engine. These were located by the driver’s feet. An NK-1 diesel fuel pump was used, with an RNA-1 regulator and carburetor. Air filtering was done by a multicyclone air filter. There was also a heater, used to heat the engine in cold winters, but also the fighting compartment. A total of three fuel tanks were in the vehicle, two in the fighting compartment and one in the engine bay, for a total of 540 liters (143 gallons). Two (90 liters each) external fuel tanks were on the engine deck. These were not connected to the fuel system and were meant to be dismounted when entering battle. The engine allowed the tank to reach a top speed of 37 to 40 km/h (23 to 25 mph). The fuel range was around 180 km (112 miles).

The rear of the Object 704, where differences in the engine plate compared to the IS-3 can be seen, such as the tow hook placement. Source: Warspot

Armor

Protection was one of the main focuses of the Object 704 project. All armored plates were welded with heavy sloping all around the casemate. The front plate was 120 mm thick, angled at 50°. The lower plate was 100 mm (or 120, sources are conflicting or might imply there might have been different thicknesses proposed) angled at -55°. The mantlet had two layers of rounded 100 mm cast armor. The side was 90 mm angled at 15° from the side. Even the rear casemate armor was 80 mm at 21°. The tank was immune from the front to the 88 mm PaK 43 L/71 gun of the Tiger II, which it never got to fight. Despite this thick armor, the vehicle still had an acceptable weight of 47.3 tonnes (52 US tons).

This was a very well protected vehicle. The thin (3 mm) sheets “hiding” the heavily sloped lower casemate armor can be seen. Source: Soviet Heavy SPGs, 1941-1945 page 38.

Test results

The SPG was finished by mid-June of 1945. It was sent to Moscow Factory No.37, from where it was taken to the state proving grounds at Kubinka. Originally, testers noted that the fighting compartment was cramped but later changed to praises for the commander’s and driver’s stations and their placement. The People’s Commissariat of Armaments asked to move the Object 704 to the Leningrad Artillery Research Experiment Range, to test the gun and artillery capabilities. Despite this, the vehicle was still sitting in Kubinka. A test program letter for the ML-20SM was also sent in July 1945. It was only in August when tests were approved but only began by September because Factory No.172 engineers did not arrive at the testing grounds. They finally arrived by the 24th of September, only to leave a few days later, leaving behind only an engineer which did not have authorization for any testing work! This outright comical timeline of bureaucracy delayed the testing of the Object 704 by six months. By the 13th of November, Kuznetsov and chief designer Nazarov finally arrived from plant No. 172. Testing was done from October until the 13th of November, through which 65 shots were fired for indirect fire and 244 shots for direct fire.

A letter summarising the results and opinions after tests was published.

  • Loading tray: No complaints other than the corners should be rounded, to make passing between the loader’s station and the breech operator easier.
  • Sights: The TSh-17 was comfortable and in a good position in relation to the gunner’s eye. The offset of the sight was negligible after 40 shots (it is safe to assume after more shots, the offset would be noticeable).

Fighting compartment notes

Several interesting remarks were made in relation to the superstructure and the design of the fighting compartment.
– The gun mantlet had no access port for the much-needed recoil brake. This meant that measuring the hydraulic fluid and releasing air was impossible.
– The hole below the gun mantlet (for depression of the gun) accumulated water.
– The sloping on the side walls made stowing ammunition difficult and complicated. Making the walls vertical was suggested.
– The headlight was mounted on a solid mount. Because of this, it shattered during firing trials. A movable spring stand was recommended.
– The commander’s position was praised, it was put facing forwards and the new hatch made battlefield observation easier and more effective.
– Both the gunner’s and driver’s stations were praised and deemed as an improvement over previous heavy SPGs.
– The loader’s position was actually considered spacious. The report stated that taking out the 12 rounds next to him could be done with ease. However, the 7 rounds on the opposite wall were noted to be hard to reach and load.
– In contrast, the breech operator’s station was noted to be cramped, especially when the gun was traversed to the left, bringing the breech to the right. Extracting the 16 propellant charges to the right side of the tank was not ideal due to the tight space. The other 4 charges beneath the gun were impossible to take out in combat conditions.

Other conclusions were:
– Wear on the barrel and muzzle velocity drop was typical, considering the caliber of the gun. After 309 rounds (244 of which with maximum charge), muzzle velocity dropped by 0.8%.
– The muzzle brake simplifies production and improves observation of the target after firing.
– Recoil brake performance is satisfactory, but the problems with access to it still stand.
– No unexpected wear or deformation occurred on the gun.
The gun had no malfunctions with the exception of failure to extract shell casings that had been used several times (as much as 10 shots).

Conclusion and fate

The Object 704 had clear advantages over the ISU-152. These included the lack of a muzzle brake, improved protection, and position of the driver and commander. The issues that were found, could, and most likely would have been addressed, if it would have entered production. The tank’s entry in service was hindered by bureaucracy and failure to get it to testing. The loss of time meant that the IS-4 was nearing serial production, making the IS-3 and a SPG based on it obsolete. With hindsight, the story of the IS-4 is, arguably, even worse. Another heavy self-propelled gun would not be built until the Object 268, based on the T-10, which had a similar fate to the Object 704.

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

You can also watch a walk around of the exterior and interior of the vehicle, made by “The Chieftain”, Nicholas Moran, here 

Illustration of the Object 704 by Pavel Alexe, based on work by David Bocquelet, funded through our Patreon campaign.

Sources:

Tankmuseum.ru
Heavy SPGs 1941-1945, Soliankin, Pavlov, Palov, Zheltov
Zveroboy, Mikhail Baryatinsky
Warspot.ru
Tankarchives.ca
Topwar.ru
Heavy SPG, A.V. Karpenko

Categories
WW2 Soviet Prototypes

Object 217, PPG

Soviet Union (1940) Mobile Machine Gun Nest – 1 prototype

The Soviet-Finnish War of 1939-1940, more commonly known in the West as the ‘Winter War’, saw many one-off vehicles being designed to help the Soviet Red Army overcome the determined Finnish defenses. Many of these never made it to the front to be tested under fire.

One example of such a unique design was the Object 217, also known as the Podvizhnoye Pulemyotnoye Gnezdo or mobile machine-gun nest.

Background

As the Soviet Red Army set about reorganizing itself in January 1940 due to its ineffectiveness in the opening month of the conflict, many meetings were held to discuss how best to tackle the various obstacles encountered in Finland.

One complaint was the lack of tank/infantry coordination. More often than not, the Soviet tanks would charge ahead and smash through the Finnish lines. The Finns used this to their advantage by allowing the tanks to pass and then reoccupying their positions soon after and shooting at the following infantry. To help counter this, several designs for infantry shields and tank-drawn armored sleds were produced by the various factories of Leningrad (modern-day St. Petersburg). These allowed for sections of infantry to be towed in relative safety to the Finnish lines in order to secure them before the Finns returned.

Clad in snow-suits and well prepared for the harsh climate a Finnish light machine gun position firing upon advancing Soviet troops at Kollaa. Source:SA-Kuva

However, this was not always successful. Once the Finns understood the method of delivery, they used their valuable anti-tank guns to target the towing tanks, or they adapted their defensive positions in order to provide incoming fire as quickly as possible.

Another solution

Another idea was to design a machine-gun-armed tankette that could support advancing infantry. The already existing T-27 was too tall, too weakly armored, and performed too poorly in the snow. As the fighting was in full swing, a quick, cheap design was needed. The task of designing such a vehicle was given to Special Design Bureau No. 2 of the Leningrad Plant of Experimental Engineering No. 185, also known as the Kirov Plant, under the leadership of Josef Yakovlevich Kotin. Kotin created a team under Leading Engineer L. E. Sychev and given the project designation of ‘Object 217’. It was soon called Podvizhnoye pulemyotnoye gnezdo or mobile machine-gun nest by the team.

The finished Object 217 prototype. Source:- https://i.pinimg.com/

The design team quickly produced technical drawings based around a four-speed motorcycle engine with simple suspension. By the beginning of March, a prototype was ready and sent for factory testing. Another four prototypes were also being constructed for trials. The assessors were initially impressed with the vehicle as it fulfilled all the requirements laid out in the request. Even so, the design had numerous drawbacks that called into question its usefulness.

The two Degtyaryov DT machine guns had limited arcs of fire, the crew positions caused discomfort and fatigue within short periods of time, and the armor was seen as too weak when coupled with the limited mobility. However, none of these deficiencies was the reason for not adopting the machine. On 13th March 1940, the Winter War came to a close and there was no longer a need for such a niche vehicle. As a result, the Armored Directorate of the Red Army canceled the project. All the prototypes were scrapped.

Specifications

Hull

The Object 217 used a single-piece of rolled armored steel to form the main body of the vehicle. To this were welded and riveted the side and rear armor. The designers wanted to minimize the silhouette. To do this, they created an oddly laid out fighting compartment. The two crew members sat with the two access hatches on top of the vehicle open during transportation, but when in combat they would adopt a prone position, lying face down inside. At its maximum height, the Object 217 measured only 55 cm. To allow the crew to see, they were each provided with simple periscope devices that protruded from the roof and covered in an armored box. However, this meant that the two crew members had no visibility to their sides and rear.

The commander was seated on the right side, with the driver on the left side of the vehicle.

A headlight was present on the right-hand side, while a smaller rear light was also present on the left-hand side.

A model of Object 217, showing the layout of the hull. The added side vision slit is not seen in the photo of the real vehicle. Source: https://topwar.ru/

Engine and Transmission

To keep the costs down, a PMZ motorcycle 16 horsepower two-stroke, 2-cylinder, air-cooled petrol engine was used for this vehicle. This allowed for limited self-propulsion which was not an issue, as the deployment of the vehicle involved being towed behind a T-26 until it reached the Finnish defenses and then unhooking itself. The transmission was a three-speed gearbox seated next to the engine. A simple friction clutch system controlled by a set of levers was used to control the movement of the vehicle. The factory tests gave a top road speed of 18.5 km/h and a cross country speed of 7 km/h. Due to the large size of the engine in comparison to the internal space available, it was necessary to create an armored box at the rear of the vehicle with several access panels.

The trials also showed that the Object 217 was capable of climbing 30-35 degree inclines and could clear trenches 1 meter wide. It could also wade through streams and puddles so long as they did not exceed half a meter in depth. How this would have translated to the Karelian Isthmus though is not known. The relatively low ground pressure was ideal for getting across the snow but the varied terrain, especially at the specially selected areas of the Mannerheim Line, would probably be taxing on the vehicle.

The same model, clearly showing the engine box. Source: https://topwar.ru/

Running gear

The Object 217 was given a very simple running gear. This consisted of four large cast spoked road wheels which were fixed to rigid axles. To provide power, a drive wheel, about half the size of the road wheels, was installed at the rear. The front road wheels could also turn like the wheels on a car, bending the track in order to allow the vehicle to steer, in a similar style to the later Light Tank Mk VII Tetrarch. To lower the amount of dust and snow thrown up by the tracks, the front and rear had protruding fenders.

The lack of suspension was one of the biggest drawbacks to the design. It put a considerable strain upon the crew, especially under combat conditions that required them to lie down. After only a short while, the assessors reported fatigue which would only make the combat effectiveness of the vehicle worse.

Armor Protection

For the type of vehicle and time, the Object 217 boasted an acceptable armor layout. The front consisted of a rolled single piece of armored plate measuring 20 mm in thickness. The sides were 10 mm thick rolled single pieces that were mainly welded upon the body, with a few rivets in the rear of the vehicle to help strengthen it. The roof and underside were 8 mm thick rolled armored plates. The advanced use of single rolled pieces of armored plate coupled with a heavy reliance on welding gave it a great amount of protection against small arms and shell fragments.

The assessors did express concern about the armor’s ability to withstand anti-tank gunfire or near hits by artillery but this was less about the armor and more about how the limited mobility meant an overreliance upon the armor for protection.

An original document showing two views of the Object 217 vehicle. The upper photograph is already known, but the lower one shows the hatches open, giving information about the upper part of the vehicles. Source: Radikal.ru

Armament

The original directive stipulated that the vehicle had to be armed with a machine gun. This was due to its main task being to keep the Finnish defenders suppressed. The design team added two Degtyaryov DT machine guns in ball mounts which would be aimed using the attached sights. These allowed for 20 degrees of travel in all directions, but this was limited more due to ergonomics within the hull rather than the installations themselves. The sides of the hull contained racks for 25 pan-type magazines, giving a total ammunition amount of 1,575 rounds per gun. In order to allow the crew to maintain operation without the need to clear spent shell casings, each gun mount had a specially designed bag that connected to the side ejection port.

Analysis of possible use

It is not sure how Object 217 would be deployed but some speculations can be made based upon the tactics used by the Soviets during the second offensive phase of the Winter War.

Possibly, after a heavy artillery bombardment upon a section of the Finnish line, a squadron of 12 T-26s would set off, 2 towing Object 217s and 4 towing Sokolov sleds (each carrying 5 Soviet soldiers). As the tanks neared the line, they detached the tow cables and the soldiers advanced to the trenches. The Object 217s would take positions on the flanks, suppressing the Finnish defenders. With these types of tactics, which were deployed during the second offensive phase, but with T-26s taking the role that the Object 217s would have played, it would allow for more tanks to be pushed into the breakthrough and still have the Infantry secure the position. The vehicles could then use their own power to cross the trenches and be ready for any Finnish counterattack.

Conclusion

The Object 217 was a unique vehicle designed for a unique situation. As the Soviet advance stalled by the indefatigable Finnish defense in December 1939, the Soviet Red Army needed any solution to breakthrough. The solution of an armored machine gun position attached to the infantry was a quick fix as it negated a lengthy rework of the current Soviet tactics. The final vehicle produced, however, was inherently flawed as a design. With such extremely limited visibility and a very uncomfortable fighting position for the crew its combat potential was small. The crew would become rapidly tired and the mobile and adaptable Finns would no doubt have quickly learned of its serious limitation and come up with tactics to exploit its weaknesses using their mobility to get around it. With the end of the Winter War the serious deficiencies of the design were never shown by actual combat but the fact that this design was not repeated again is perhaps the strongest indication that this unique vehicle was not an effective solution to breaching well prepared enemy defences. To do that would rely on a far better use of coordinated operations and flexible vehicles supported by artillery – something the Soviets repeatedly failed to manage during the Winter War.

The very small Object 217 mobile machine gun nest was a very peculiar vehicle, very low, with the engine in a small box at the rear. Illustration by Yuvnashva Sharma, funded by our Patreon campaign.

Sources

Komolyets, Maxim. Tanks in the Winter War: 1939 – 1940 (Operations: Scandinavia 1939) (Leandoer and Ekholm (April 14, 2009))
https://warspot.ru/2973-proekt-217-mobilnaya-ambrazura
https://topwar.ru/105675-podvizhnoe-pulemetnoe-gnezdo-tanketka-obekt-217.html

Categories
WW2 Soviet Prototypes

Object 257

USSR (1945) Heavy tank – none built

The IS-7 (Object 260) is one of the most well-known tanks developed by the USSR, in part due to its massive size and weight, placing it with the likes of Tiger II. However, few know about its lengthy and intricate development process, consisting of many years of work and prototypes, with a total of seven different prototypes sharing the name IS-7. One of these was the Object 257, the bridging in between the failed IS-6 and the renowned IS-7.

‘Baby’ IS-7

In February of 1945, a replacement program for the Object 701 (IS-4), which had just started development seven months earlier, was requested by the GABTU (Main Directorate of Armored Forces). The SKB-2 factory, which designed the Object 701, was too busy with it and was working on its production. This left a window of opportunity for Factory No.100 to take over and begin work on the IS-4 replacement. Factory No.100 had just lost to SKB-2, as the Object 252 and 253 (IS-6) were deemed inferior in many ways to the Object 701. An upgrade to the Object 252, known as the Object 252U, was made in November of 1944, using pike-shaped angled armor with help of engineers from NII-48 research institute. However, the changes were not able to revive the already canceled IS-6. Despite its failure, it served as a good basis for the upcoming heavy tank.

Illustration of Object 252U, on which Object 257 was largely based. Illustration by Pavel Alexe.

On 7th April 1945, requirements for a 122 mm tank gun with a muzzle velocity of 1,000 m/s (3,280 fps), two-part ammunition, and a rate of fire of four rounds per minute (15 seconds reload) were issued. Factory No.100 had already done work with OKB-172 on the BL-13 gun which was used on the late alterations of the Object 252 and 252U. Earlier prototypes of the IS-6 had the D-30. This new gun was called BL-13-1 and featured improvements over the BL-13, such as a mechanical gun rammer, increasing its rate of fire to a whopping 8-10 rpm. Even a mechanical autoloader was tested, but, despite its claimed solid reliability, it was sluggish and was not worth losing a crew member on. It also decreased the rate of fire to 7-8 rounds per minute at a higher price tag. Nonetheless, the idea was never fully dropped, as the final IS-7 prototype used a loading assistant, using a conveyor belt. The shells were however larger, as the gun had a 130 mm caliber.

Work started on the new heavy tank in May 1945 with P. P. Isakov, who had previously worked on the Object 252U and IS-2U projects, as chief designer. The turret was taken directly from the Object 252U, and so was the pike-nose design. The engine and transmission, rather interestingly, were taken from the Object 253, the IS-6 variant which used a mechanical-electrical transmission, which caught fire during trials, was expensive and unreliable. The biggest change was made to the lower hull and suspension. This project would get the designation Object 257 and was the first design to get the name IS-7.

Design

As mentioned earlier, many elements from the IS-6 program were used in Object 257. The turret and pike nose came from the Object 252U and the engine and transmission from the Object 253. However, one of the main focuses of the Object 257 project was sturdier protection. The same principle applied on the pike nose, which was implemented on the side of the hull as well. The previously flat hull sides were now angled inwards at an extreme angle, forming a diamond shape silhouette from the front and rear. On the downside, this caused huge internal problems. Primarily, torsion bars could no longer be used, since the hull was too narrow, meaning that the suspension had to be moved on the outside of the hull. For the suspension, four volute springs were mounted on each bogie, with two wheels per bogie, a very similar design to that of the American M4 Sherman. This made the Object 257 one of the most unique looking Soviet heavy tanks of the post-war era, as this was the first time a Soviet tank used volute spring suspensions.

The turret was identical to that of the Object 252U, being heptagonal and of a low profile. Inside, the gunner was seated to the left of the gun, with the commander behind him. The loader was located to the right of the gun. A coaxial machine gun was also mounted to the right of the gun, and could be fired by the gunner. It is unclear if it was a 7.62 mm SGMT machine gun or a 12.7 mm DShk heavy machine gun. The loader was responsible for loading this weapon as well.

Cutout line drawing of the Object 257. The pike nose armor can be seen. The problems created by the armor layout and low profile are clear. The gun has little room to depress and the driver is very cramped. 5th June 1945. Source: Yuri Pasholok

Crew

As the Object 257 focused mainly on protection, crew comfort and overall ergonomics of the tank had to be sacrificed. The pike-like front end of the vehicle decreased the amount of space available for the driver. As shown in the drawing, the driver’s pedals would be located high up, his feet being on the same level as his torso. This would have been uncomfortable, especially when driving for longer periods of time. The driver had an entry and exit hatch on top of him, however, it was directly under the gun, meaning that entering and exiting would have been frustrating when the barrel was over the hatch. To add to his misery, he only had one periscope, relying more on the commander for command.

The gunner and commander could sit on chairs mounted to the floor through a long arm. Even for them, the conditions were not great. The low turret profile gave them very little headroom, not to mention it restricted the main gun from depressing more than a few degrees. The commander’s position lacked a cupola, and only had one periscope facing forwards and one backward. This further limited his visibility.

Cutout front and rear view of the Object 257. Many interesting details are made clear here, such as the Y-shaped seat support and interesting ammunition placement. Source: Yuri Pasholok

The loader was to the right of the gun, having to push the shells in with his left arm, a rather large inconvenience, considering the size and weight of a 122 mm shell. In addition, the ammunition was made out of two parts, the shell and the cartridge. In a turret bustle at the back, 30 rounds were stored, protected by an armored case. The cartridges were stored along the sides of the hull, diagonally, meaning that if one cartridge was taken out, another could possibly slide down. This, however, is only speculation. The average loader could load the gun in around 15 seconds. More warheads were stored in the hull, behind the driver. All this meant that the loader could easily load in the warheads, but had to bend down to grab a cartridge. As indicated earlier, an autoloader system was designed, however, despite its reliability, it was slow. If an autoloader was used, it is unknown if the loader would have been dropped or he would have had other tasks.

Armor

One of the most interesting aspects of this tank is the armor layout. The pike nose was an increasingly common feature in Soviet heavy tanks of the time. It was 150 mm (6 inches) thick, angled at 28° from the side. Yet the lower hull was completely new. Instead of flat plates, like on the IS-6, the plates were angled inwards, forming the same effect as a pike nose. This would have helped immensely against incoming rounds, deflecting them into the ground. The top parts were 150 mm (6 inches) thick and angled at 30°. The bottom plates were 85 mm (3.3 inches) thick angled at 23°. This thickness was not maintained all the way to the bottom of the hull. Halfway in, the armor was thinned down to only 20 mm (0.8 inches) yet kept at the same angle. This was most likely done to save weight, as the chances of enemy fire hitting this area were rather low, with the large suspensions being in front. The new side armor was impenetrable to the German 105 mm Flak 39 and the front was even strong enough that the BL-13-1 gun could not penetrate it at point-blank range. The turret armor was thick as well. The sides, although tinner in some areas, since they were curved, were 150 mm (6 inches) thick, angled at 45° degrees. Of course, this came at a cost. The weight of the hull increased to 23 tonnes (25.3 tonnes) over the IS-6’s 21 tonnes (23 tonnes).

Side armor comparison of various Soviet heavy tanks of the time. The newly introduced IS-3 was rather small compared to the Object 257. Consider that, at that stage, the Object 257 was still called IS-7 (ИC-7). To the right, the Object 701 (IS-4) hull can be seen, which was, at the time, the most heavily armored Soviet tank. The IS-6 (ИC-6), on which the Object 257 is based, is in the top right. Source: Yuri Pasholok

Suspension

If there is something that makes the Object 257 stand out, it is the suspension. As previously stated, the lack of room in the hull meant that the suspension had to be moved on the outside. Curiously, a bogie with four volute springs per wheel was used. These were very similar to the M4 Sherman medium tank, and it is entirely possible the design was derived from it. The wheels were mounted on opposite sides of the bogie and had arms on either side. These arms would then be attached to two volute springs that compressed when the wheel moved upwards.

M4 Sherman in Soviet service. The Russians used American equipment throughout the war. This was likely the inspiration source for the suspension on the 257.
Source: The Sherman Tank Site

Engine

As the weight had been increased up to 55 tonnes (60 US ton) on paper, a new engine was needed. Since 1944, Factory no.77 had been working on a new engine, based on the V-2, called V-16F. It was coupled to a similar (if not the same) electric transmission used on the Object 253. However, this engine was deemed very poor. Trials took place between March and May of 1945 and it was found to be unreliable. Even supercharging the engine to 600 or 750 hp that the IS-6 and IS-4 had would have put a huge strain on the engine, and failures occurred. Even at 520 hp, the engine was faulty. However, an engine this underpowered would have been disastrous if mounted on a 55 tonnes heavy tank, considering a 50 km/h (31 mph) speed was wanted. Further development was done on the V-16F, however, efforts were abandoned, and improved V-12 engines were used on the further IS-7 project.

The unreliable and weak V-16F engine initially proposed for the Object 257. Considering its many issues, it was left behind and V-12 engines were re-used in the IS-7 program.
Source: Yuri Pasholok

New German heavies and Conclusion

After the discovery of the Maus and Jagdtiger and their analysis, the armor on the Object 257 was deemed insufficient. The 128 mm KwK 44 guns of the Jagdtiger and Maus would have pierced the hull. Likewise, the armor on the Maus and Jagdtiger was too strong for the BL-13. All this meant that the Object 257 needed to be reworked significantly. In addition, on 11th June 1945, the requirements of a new heavy tank were set by the GABTU. The weight increased to 60 tonnes (66 US tonnes) and the new armament was to be an S-26 130 mm gun. Lastly, torsion bar suspension was required. The Object 257 clearly was not adequate, leaving factory No.100 to start work on a new heavy tank. Nonetheless, work was not in vain, as the experience gained and armor features of the Object 257 were passed on. Many other tanks were designed, until the final Object 260 was made, the IS-7 we know today.

Illustration of the Object 257 by Pavel Alexe. The similarity to the suspension of the M4 Sherman can be seen.

Sources

https://warspot.ru/2793-elektrostalin-6
https://warspot.net/9-object-257-the-first-is-7
http://www.tankarchives.ca/2019/03/modernization-on-paper.html

Object 257 specifications

Dimensions (L-W-H) 7.375 x 2.430 x 3.390 meters
(24 x 9 x 11 feet
Total Weight, Battle Ready 55 tonnes (60 US tons)
Crew 4 (Commander, Gunner, Loader and Driver)
Propulsion V-16F engine and electrical transmission
Speed 50 km/h (31 mph)
Armament 122 mm BL-13-1 2-part ammunition gun
co-axial 7.62 mm SGMT machine gun
Armor Hull armor
Front top plate: 150 mm at 28°
Front bottom plate: 150 mm at 40°
Side top plate: 150 mm at 30°
Side bottom plate: 85 mm & 20 mmTurret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
Total Production 0; blueprint only
Categories
WW2 Soviet Prototypes

Object 252 Improved, ‘Object 252U’

USSR (1944) Heavy tank – none built

The Last breath of the IS-6

In the later years of the Second World War (‘The Great Patriotic War’ to the Soviets), there was a quest to develop a replacement for the IS-2 heavy tank. The development process resulted in the IS-6 (Object 252/Object 253) and IS-4 (Object 701). This program was as secret as it was ambitious, with two rival factories working on their designs in absolute secrecy in fear of leaking information to one another.

On paper, the IS-6 seemed superior to any Panzer in Germany’s arsenal at the time. However, due to its mechanical issues and overall poor performance, it lost to its competitor, the IS-4, which would go on to enter service in 1946. Despite this, a last ditch effort to revamp the IS-6 was made, with limited success. This renewed vehicle would become known as the Object 252 November improvement – more commonly known as the Object 252U.

Name

The Object 252 upgrade from November 1944 might have never gotten an official designation. Yet modern historians and video game company Wargaming have called it Object 252U, with the ‘U’ probably coming from the romanized Russian word ‘улучшенный’ (uluchshennyy). For simplicity’s sake, we will refer to it as Object 252U for the rest of the article.

Development

After the battlefront experiences of 1943, with the appearance of the new German heavy tanks and tank destroyers such as the Ferdinand, the Soviet Union quickly realised that a new heavy tank was needed. Thus, in November of 1943, the GABTU (Main Directorate of the Armed Forces) requested the development of a 55 tonnes (61 tons) heavy tank.

Two factories of the same organization (ChKZ) and the same city, Chelyabinsk, were assigned this task.

1. SKB-2, which was headed by Nikolai Dukhov, who had taken part in the development of the IS tank, and would later become the assistant of the chief designer of the Soviet atomic bomb plan. SKB-2 designed the Object 701, which was a planned upgrade of the IS-2 and later became the IS-4.

2. Experimental Factory No. 100, which was headed by Josef Kotin, who previously had done work on countless Soviet tanks. In contrast to their ‘opponents’, they developed a completely new tank, the Object 252 and 253.

From June to October 1944, Factory No.100’s Object 252 and Object 253 (IS-6) failed in comparison to the SKB-2 design. The armor was much thinner than that of the Object 701, yet it was still heavy, weighing over 50 tonnes (55 tons). The mechanical problems in the suspension and mobility were worse compared to its heavier counterpart. Kotin managed to get the IS-6 to Moscow, where it got tested against the Object 701, but to no avail. In late November of the same year, an upgrade attempt was made with the help of the NII-48 institute using a heavily angled pike-nose design for the armor and a new turret. Despite it being a dead-end when it came to the development of the IS-6, it was a turning point for future heavy tank designs. This is now known as the Object 252U.

Outline of the November, 1944 Object 252 upgrade, commonly known as Object 252U. The U comes from the romanized Russian word улучшенный, meaning ‘improved’. It is hard to tell if this is an original name or a modern designation. Despite the improved armor effectiveness, the IS-6 boat had sailed, and the IS-4 was chosen for mass production.
Source: Warspot.ru
Object 252U frontal view. The low profile of the tank is even more clear from this view. Source: Stalin Supertanks IS-7

Design

Naturally, the design of the 252U was similar to that of the Object 252, as it was based on the same hull. Unmistakable are the large stamped steel wheels with a 750 mm (30 inches) diameter. These were first tested on the Object 244 (an IS-2 upgrade) to be used on the Object 252. The Object 253, although also an ‘IS-6’, used regular IS style wheels. The engine and the rear and side of the hull were untouched on the November improvement. The torsion bars suspension would remain the same too.

The engine would most likely have been the same as on the Object 252, a V12U diesel engine producing 750 hp at 2,100 rpm. The internal fuel tanks had a capacity of 650 liters (172 US gallons) but, in typical Soviet fashion, there would have been 4x 100 liter (26 US gallons) external fuel tanks on the sides.

Interesting to add is that the early designs for the IS-6 actually had a rounded frontal hull, similar to that of the much later Object 279, yet having a similar effectiveness to the Object 252U. The actual prototypes had a hull made of angled flat plates, probably because it was much easier and cheaper to produce compared to a large casting.

Early drawings of the IS-6 with a UFO-like shape, akin to the much later Object-279
Early drawings of the IS-6, by that time considered as an “IS-2 upgrade”. The curved hull that transpired onto the Object 252U is somewhat apparent.
Source: Stalin Supertanks IS-7
Factory No.100 IS-2 upgrade proposals. In the middle is the IS-2, while to the left is the rounded hull version and to the right is the flat plates version. This latter one would then become the IS-6.
Source: Warspot.ru
Object 252 with its larger road wheels. These large roadwheels, designed by N.F. Shashmurin proved to be faulty on the IS-6 – needing replacements every 200 to 300 km. In fact, 14 of these wheels were replaced during its 825 km testing. Note the BL-30T gun, which was to be replaced by the BL-13T. However, this idea never left the drawing board.
Source: Bron Pancerna, Flickr

The most notable changes appeared in the hull and turret. The NII-48 institute strongly suggested that, in order to improve the protection yet not increase the weight, a pike-nose design should be used. This meant two diagonal plates were welded in the front, creating a pike-like shape and greatly improving the effective armor on the front of the vehicle from threats directly in front of the vehicle. This was designed by engineers V. I. Takarov and G. N. Moskvin, which went on to later design the Object 257 as well.

Previously, the Object 252 and 253 used the D-30T 122 mm gun. This offered very little improvement over the standard D-25T from the IS-2, yet the price was almost doubled. As a result, a new gun was planned to be added to the Object 252, although it ended up never being fitted. The new gun was the BL-13 122 mm, developed in December of 1943 by OKB-172 and was a combination between the D-25T and the BL-9 gun barrel. Further work was done between Factory No.100 and OKB-172, with the gun being ready by July 1944. The capabilities of this weapon are unknown. A ready rack for the massive projectiles was located in the rear of the turret, covered by a thin protective casing, an overall design similar to modern MBTs. A total of 18 warheads were stored here. The casing with explosive material was stored within the hull, on the exact opposite side. This made loading the warheads relatively easy, however, the placement of the cases required the loader to bend down, and manhandle them up into the breech.

The new turret and BL-13T gun that was to be mounted on the IS-6. The tiny space between the top of the breech and the roof of the turret indicates extremely poor gun depression.
Source: Weaponsandwarfare.com

Crew

As the Object 252U was, for the most part, very similar to the IS-6, the crew compartment was mostly identical. It had a crew of four, a commander, gunner, loader and driver. The gunner sat to the left of the gun with the commander behind him. They seem to have shared the same entry and exit hatch, which could be fatal for the gunner in case of a need to evacuate quickly, as he would have to wait for the commander to exit first. The commander had no cupola to look out from, rather just two periscopes (one pointing forwards and the other backward) on top of his hatch. This would have made the commander almost blind when buttoned up. The commander was also in charge of the radio. The loader, as discussed above, had a tough time when loading the main gun. As the cases for the rounds were in the hull, he would have needed to get off his chair and lift them up. Since the turret had no basket, the crew members in the turret could either sit on seats attached to the turret or stand on the hull floor. The loader seems to also have been tasked with the operation of the 12.7 x 108 AA DhSK heavy machine gun. To operate it, the loader had to expose himself, by partially climbing out of his hatch. It is also entirely possible that he was also responsible for loading the co-axial machine gun, a 7.62 mm SGMT. The driver was located in the hull, with the hatch directly underneath the gun, potentially making it very difficult to exit, if the gun was pointing forward.

Since the Object 252U put such a large emphasis on protection, crew comfort and ergonomics were sacrificed. The angling of the hull armor plates made storing ammunition and overall life inside cramped and claustrophobic. An awful thought for many western tankers, Soviet tank design doctrine often sacrificed crew comfort for protection or a low silhouette.

If the IS-6 or Object 252U would have entered service, it would have most likely received a series of upgrades to fix the problems mentioned above, like the periscopes. The Object 701 had its periscopes altered and more added several times until full scale production. However, the armor profile and no turret basket were still features of future Soviet heavy tanks.

Armor

It was regarding armor that the IS-6 struggled the most in comparison with the IS-4. The front was one 100 mm (4 inches) thick flat plate angled at 65°. The lower front plate was 120 mm (4.7 inches) thick, yet only angled at 52°. The side armor at the thickest, was 100 mm. Testing was done in Kubinka, Moscow with captured German 88 mm and 105 mm guns, which could not penetrate the upper frontal plate from 50 m (55 yards). The 120 mm lower plate, being less angled, was penetrated from a “shorter distance”. These results, while being better than the IS-2 and IS-3, fell short of the protection offered by the IS-4. In this regard, the new pike nose design of the Object 252U came into play, as the lower plate was still 120 mm thick, but more sharply angled at 28°. The two upper plates forming the pike nose were 100 mm thick, yet angled at 16° from the side. This increased the effectiveness of the armor significantly. The rest of the hull remained the same as that of the regular IS-6.

Testbed of an IS-6 hull after firing tests possibly using German guns. Despite being well angled, the protection was not deemed strong enough, considering its weight. Note the heavy interlocking plates. It might come apparent that there is no access hatch for the driver. This, however, was a simplified and shorter mockup, purely designed to test the effectiveness of the angled armor. Having a full-size hull, with hatches and other components would have been too costly and time consuming for this purpose.
Source: Stalin Supertanks IS-7
Testbed of the IS-6 hull after firing tests, view from the side.
Source: Stalin Supertanks IS-7

IS-2U

With the help of NII-48, Factory No.100 also designed the IS-2U simultaneously with the Object 252U, making an IS-2 with a pike-like front hull. An improved version of the IS-2, it featured a new gun, and the pike-nose frontal armor. Like the Object 252, it was rejected, in favor of SKB-2’s Kirovets-1, which later became the IS-3.

Blueprints of the IS-2U, sometimes erroneously used to show Chinese heavy tanks. Although the program itself was different to the Object 252U, the pike-nose armor was designed by the same engineers, Tarotko and Moskvin.
Source: Warspot.ru

Fate and Conclusion

The Object 252 November upgrade never went past the blueprint stage, as the fate of the IS-6 had already been sealed. Yet, despite being unsuccessful, the design was not in vain. Instead, it served as a basis for the Object 257, which in turn led to the IS-7 heavy tank, the heaviest Soviet tank ever built. More importantly, it was one the first Soviet designs to implement the pike-nose design, which became famous with the IS-3, and was implemented in the majority of Soviet heavy tanks until their discontinuation.

Illustration of Object 252U by Pavel Alexe, funded through our Patreon campaign.

Sources

Supetanki Stalina IS-7
https://warspot.ru/2793-elektrostalin-6
https://warspot.net/9-object-257-the-first-is-7
http://www.tankarchives.ca/2019/03/modernization-on-paper.html

Object 252U specifications

Dimensions (L-W-H) 7.50 x 2.4 x 3.3 meters
(25 x 7.8 x 10.8 feet)
Total Weight, Battle Ready 50+ tonnes
(55 tons)
Crew 4 (Commander, Gunner, Driver & Loader)
Propulsion V12U diesel engine, 750 hp at 2,100 rpm
Speed 35 – 50 km/h (hypothetical)
(21 – 31 mph)
Range 400km
(249 miles)
Armament 122 mm D-13 2-part ammunition gun
12.7 x 108 mm DShK heavy machine gun on roof
co-axial 7.62 mm SGMT machine gun
Armor Hull armor
Frontal plates: 100 mm forming pike nose at 16°
Lower plate: 120 mm angled at 38°
Upper side plates: 100 mm angled at 45°
Lower side plates: 100 mm at 90°
Upper rear armor: 60 mm at 60°
Lower rear armor: 60 mm at 30°
Upper hull armor: 30 mm
Floor armor: 20 mmTurret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
Total Production Blueprint only
Categories
WW2 Soviet Prototypes

SMK

USSR (1939) Heavy Tank – 1 Prototype Built

The More Turrets, the Merrier?

Right from the very beginning of the development of the tank concept, the idea that tanks could have multiple turrets to do multiple tasks at the same time was one that was very popular. Japan, Germany, the USA, and Poland all experimented with multi-turreted tanks, but none so much as the USSR and Great Britain. In the early 1930s, the UK produced the A1E1 Independent, Medium Mark III, Vickers 6 ton, and A.9 Cruiser multi-turreted tanks. The Soviet Union had produced the T-26 (a Vickers 6-ton copy), T-28 (based from the Medium Mark III), and the T-35A multi-turreted heavy tank, perhaps the most impressive multi-turreted vehicle to be manufactured in the Soviet Union.

T-35A chassis number 196-94, after being captured by German forces on June 24th, 1941. This vehicle was a prototype that was given some ‘updates’ to try to improve the longevity of the T-35 series. Source: Francis Pulham Collection.
The T-35A was, on paper, an impressive vehicle, but in reality, the vehicle was seriously flawed. It was too long, leading to major structural and mechanical problems, especially when turning, also being too tall and therefore dangerously overbalanced (during WWII, two T-35s would topple over due to the high center of gravity), and too many turrets which left the commander unable to adequately control the numerous crewmen and guns. It became clear that the T-35A was in desperate need of modernizing. T-35A chassis number 183-5 (the twenty-sixth T-35A manufactured) was taken to the testing grounds at Kubinka, near Moscow in 1936 and extensively trialed. After a year of these trials, it was decided that the T-35A was generally unfit for service. In the short term, the T-35A was moderately ‘updated’, but design bureaus were soon busily at work drawing up the Soviet Union’s new multi-turreted heavy tank.

Shaking up the Red Army

Dmitry Grigoryevich Pavlov was the Soviet commander in Spain during the Spanish Civil War during 1936 and 1937, and his experience fighting the Nationalist forces there had quickly seen him gain power within the Red Army. Eventually, in 1937, he found himself in charge of the ABTU (Armor and Automobile Management Bureau). Pavlov was very important in establishing the groundwork for a total overhaul of the Red Army’s tanks, some of which he had seen to perform poorly during the Spanish Civil War. While the main Soviet tank sent to Spain, the T-26, was highly regarded, it was often knocked out by light guns due to the thickness of its armor. The T-26’s armor plates were no thicker than 12 mm, almost no better than the tanks of World War One. This proved to be a major flaw with not only Soviet tanks but tanks all over the world.
In 1937, Resolution 94ss was passed. This was a general order from Pavlov for a total review of the entirety of Red Army stocks. Factory KhPZ 183 (Kharkov Locomotive and Tractor Works) was ordered to begin prototyping for a new multi-turreted heavy tank to replace the T-35A, and a new fast convertible tank to replace the BT-7. Despite this, KhPZ 183 found itself out of its depth developing two new tanks and was busily focusing on the BT tank replacements, the eventual A-20 and A-32, which led to the T-34.
Due to KhPZ 183’s inability to begin designing a new heavy tank, the project was partly handed over to Factory 185. After this, the Kirov Works was also invited to design a new multi-turreted heavy tank for the Red Army. On paper, three factories were now designing a multi-turreted heavy tank, these being KhPZ 183 (which had still technically had not pulled out of this race), Factory 185, and the Kirov Works.
By May 1939, Factory 185 had drawn up the T-100 heavy tank, and the Kirov Works had named their vehicle the SMK, after Sergey Mironovich Kirov, the short-lived chairmen of the CPSU (Communist Party of the Soviet Union) in 1934, who was assassinated not too long after. Much can be said on the death of Kirov, such as whether it was under the orders of Stalin himself, but nevertheless, after his death, Kirov became a much-celebrated figure in Soviet mythology. KhPZ 183’s project had not begun, and therefore at this stage, it became a two-horse race.

‘We are building a tank, not a department store!’

The SMK was originally designed with the T-35’s suspension, but this was deemed inadequate. Therefore, testing was conducted with a T-28 that had its suspension replaced by torsion bars. While not a total success, the potential was not lost on the engineers, and it was decided to implement this into the design.
There were now two tanks on the table, and both vehicles had a very similar internal layout. At first glance, the T-100 and SMK looked similar, but there were very different vehicles. The T-100 had coil spring suspension with rubber-tired road wheels, a different engine, turret shape and design, armor thickness, and even main armament in the shape of the L-10 76.2 mm gun.
Both the SMK and T-100 had three turrets. The SMK prototype originally had two small turrets, one forward and one behind a central pedestal. The main turret was perched upon this central pedestal. The smaller turrets had a 45 mm Model 1934 gun, capable of semi-automatic fire (the breach automatically locked when a shell was inserted, and the spent shell casing was automatically ejected once fired) when shooting armor-piercing projectiles, and quarter automatic fire (the breach automatically locked when a shell was inserted, but the spent shell casing had to be manually removed) when firing High Explosive projectiles. The main turret was equipped with an L-11 76.2 mm gun. The three guns were accompanied by coaxial 7.62 mm DT-29 machine guns, and the main turret had a rear ball mount that was given a 12.7 mm DShK machine gun.
The chassis of the original SMK prototype was octagonal, with a substantial overhang of the upper hull over the tracks and running gear, much like the earlier T-24 tank. The forward turret was placed off-center to the right, whereas the rear turret was off-center to the left, with a large armored radiator intake to the right of the rearmost turret.
The tank was powered by an 850 hp GAM-34T liquid-cooled diesel engine housed in the rear portion of the tank. The drive sprocket was also to the rear. The prototype, on paper, had eight road wheels and four return rollers.

Prototype drawings of the three turreted version of the SMK, with the top image featuring T-35 suspension, and the lower depicting torsion bar suspension. Interestingly, the torsion bar version still retains a track tensioning wheel between the idler and the first road wheel, something not seen on the prototype. Source: https://www.dieselpunks.org
On 9th December 1938, the two prototypes were presented to the ABTU, with wooden mock-ups of the two vehicles. Both prototypes were approved, but the design of both vehicles was requested to change, and the rearmost turret was to be removed from both tanks, reducing the turrets to two, one turret with a 76.2 mm weapon, and one with a 45 mm weapon. Some sources claim that Stalin himself requested this, and the mythology of the incident describes Stalin inspecting one of the two wooden mock-ups, and snapping off one of the sub turrets, exclaiming ‘We are trying to build a tank, not a department store!’ This is not verified anywhere and is highly apocryphal of Soviet doctrine at the time. As it was, the Kirov Works was well aware of the limitations of multi-turreted tanks and was already designing a single-turreted version of the SMK.

Prototypes

From this point, the prototype was approved for production. The tank was now to only have two turrets, instead of three, and due to the weight saved from this, the desired 70 mm thick glacis was able to be introduced into the design.
Now that the chassis was shorter, the prototype was given eight cast road wheels with internal shock absorbers and four rubber-rimmed return rollers. An adjustable front idler wheel was provided for the tank.
The frontal armor was 70 mm thick, and the sides and rear plates were 60 mm thick. The floor plate was 30 mm thick, and the hull and turret roofs were 20 mm thick. The hull no longer extended over the tracks, and therefore a fender was placed along the length of the chassis.

The SMK was an imposing tank, however, the design had some flaws, including a dangerously high and exposed turret ring, a flaw that was exploited during the combat trials in Finland. Source: TSAMO via Maxim Kolomiets
The hull was split into three compartments, not including the main turret. These were the forward fighting compartment, the central fighting compartment, and the engine/ transmission compartment. The crew consisted of seven men: driver, engineer/ radio operator, 45mm gunner, 45mm loader, main turret gunner, main turret loader, and, finally, a commander.
The main turret was given a P-40 anti-aircraft mount with a station for a DT-29 7.62 mm machine gun. The radio in the hull was a TK-71-3, standard in all Soviet heavy tanks. This radio had a rage of 15 km on the move, and 30 km when stopped.
The prototype entered the construction stage in spring 1939, but the design team at the Kirov Works was not happy with the outcome. Engineers knew that the tank was too heavy, limiting its combat capability. Due to the height and weight of the SMK, the vehicle was too cumbersome to be an effective fighting machine. Ultimately, the engineers knew that the multi-turreted tank concept was fundamentally flawed. Therefore, under their own initiative, they began working on a single-turreted version of the SMK.

A cutaway of the SMK prototype as produced. The turret displays features of the vehicle when it was deployed in Finland, the rear turret-mounted DsHK 12.7 mm gun has been replaced with a DT-29 7.62 mm machine gun. Source: vesna-info.ru

Kliment Voroshilov

The Kirov Works began to design a new single-turreted version of the SMK, and the tank they designed was similar to the SMK. Instead of two turrets, the smaller turret was removed from the design, and therefore there was no need for a turret pedestal. The turret ring was now flush with the hull roof plate. The new main turret was similar to that of the SMK, with an L-11 76.2 mm gun, but this prototype, named KV-U0, was given a coaxial 45 mm gun, so as not to reduce the firepower compared to the SMK. The engine of this prototype was a 500 hp V2 diesel that had been designed for the BT series. In this case, it was supercharged. The engine was also used in the T-34, known as the V-2-34, and the version used on the KV series was known as the V-2K. The V-2K was seriously strained when powering the KV-1, but it was completely overworked when powering the KV-2, with its much larger and heavier turret.
The new tank was named after Kliment Voroshilov, who at the time was a prominent figure in the Soviet Union, being one of the five Marshals of the Soviet Union. This new KV (Kliment Voroshilov) tank was submitted with the SMK for trials at Kubinka in the late summer of 1939.

The first KV tank prototype, KV-U0 during WWII. The similarities to the SMK are striking, with the main obvious differences being the lack of the smaller turret with a 45 mm gun. Other differences include a shorter chassis, thicker armor and a different engine. Source: Francis Pulham Collection.

Kubinka trials

The T-100, SMK, and KV tanks were all taken to the Kubinka training ground to conduct trials. The SMK had an advantage over the T-100, being three tonnes lighter than the T-100, and having better cross-country capabilities, but itself was at a disadvantage to the KV tank, the surprise entry for the new role.

Front view of the SMK. Notice the off-centered front 45 mm gun turret. This was to allow for an escape hatch for the driver on the hull roof. Notice the fabric on the front fenders hanging down almost to the tracks. This was likely some measure to curb debris being kicked up. Source: TSAMO via Maxim Kolomiets

The rear view of the SMK during Kubinka trials. The engine deck was very high from the ground, with a large air intake hidden under the upper portion of the hull. At the rear of the turret is a 12.7 mm DShK machine gun. During the combat trials in Finland in 1940, this gun was replaced with the standard 7.62 mm DT-29 machine gun. Source: TSAMO via Maxim Kolomiets
The trials did not go smoothly for either the SMK or the T-100. The SMK suffered from transmission failures during the trials, which were one of the major issues that were desired to be eliminated when replacing the T-35A. It did, however, perform marginally better than the T-100. The vehicle was able to ascend an escarpment of 37 degrees and travel at 35.5 km/h.
The tank that performed best during the trials was the KV. The weight and length saved by removing the secondary turret proved most advantageous. Additionally, the commander had a much easier time controlling the actions of the tank. The KV did not completely win over the crowd, however. The V2K engine (the name for the new V2 engine) was working at its absolute limit, and the vehicle had serious trouble crossing a moat.
This testing was done in early September 1939. This was too late for combat trials in Poland, but for the Soviet Union, another conflict was on the horizon that was a prime testing ground for the new vehicles.

The left side of the SMK at Kubinka trials. The swing arms for the road wheels can be clearly seen and was one of the major improvements over earlier Soviet heavy tank designs. The two turrets are conical in shape, with the main turret consisting of four main plates, and a pressed and shaped roof to maximize space inside. Source: TSAMO via Maxim Kolomiets

Opportunity in Finland

The Winter War was a major conflict between the USSR and Finland. The war was caused by Soviet expansionism, as the USSR wanted a bigger land buffer between Leningrad and the Finnish border 20 km to the north. Initially, a peaceful territory renegotiation was held in Moscow, but Finnish diplomats were understandably unwilling to give away Finnish land in exchange for less strategic positions.
Hostilities opened on 30th November 1939, when forces of the USSR began an invasion of Finland across the entire border. However, the greatest concentration was on the Karelian Isthmus, north of Leningrad. Molotov had promised that a peace settlement between the USSR and Finland would be complete by Stalin’s birthday, 12th December. However, this did not happen, as the Finnish defenses and defensive strategy were highly effective against a Red Army that had suffered greatly from the Purges.
As the war dragged on, it became apparent that the new prototype tanks could be used in real combat situations, a real trial by fire. The three tanks, T-100, SMK, and KV, were given to a special experimental tank unit, the 91st Tank Battalion of the 20th Heavy Tank Brigade.
This unit, despite being a heavy tank brigade, was primarily made up of T-28 tanks, with 105 T-28s (which was one-fifth of the total number of T-28s manufactured), but also 21 BT-7 tanks and 8 BT-5 tanks. Additionally, 11 BMH-3 experimental flame-throwing T-26 tanks were deployed with the unit. The BMH-3 was a conversion for a regular T-26 with two turrets, converted to shoot fire from one or both turrets. It had two tanks of kerosene and compressed gas placed onto the engine deck.
The SMK arrived with the brigade after a major overhaul. One of the minor changes was that the rear-mounted DShK was replaced with a DT-29 machine gun.
The crew of the tank was mostly made up of very experienced members. The commander of the SMK was Senior Lieutenant Petin, the main turret gunner was Senior Lieutenant Mogilchenko, and other members were taken from the Kirov Works, and were generally veterans of driving and operating heavy machinery. The driver was I. Ignatiev, the mechanic was A. Kunitsyn, and the transmission specialist attached to the repair team was A. Teterev. The radio operator in the hull was pulled from regular tank units and is not named in sources.
As can be seen, the crew was a very serious roster, all being high ranking or experienced enough to be mentioned in testing reports.

Combat Trials

The 20th Heavy Tank Brigade was deployed on the Karelian Isthmus, which was the most hotly contested portion of the Soviet-Finnish frontline. This piece of land was the primary concession requested by the Soviet government, as they felt that the Finnish border was too close to the strategic port and major industrial hub of Leningrad (nowadays Saint Petersburg). It was on the Karelian Isthmus that the strongest Finnish defenses were organized, which included the famous Mannerheim Line.
The Mannerheim Line was a cleverly designed series of limited fortifications that used the harsh terrain of the Isthmus to force Soviet forces to rely on the few poor roads throughout Karelia. Anti-tank and anti-personnel traps were interwoven with trenches, pillboxes, small forts, and even deep covered ditches to trap tanks trying to cross.
One of these concrete forts was known by the Soviets as ‘Giant’ and, on 17th December, the 91st Tank Battalion, along with other battalions of the 20th Tank Brigade, were committed to the attack.


The only known photographs of the SMK during operations in Finland are these stills from a Soviet propaganda film. The SMK is moving at speed towards the front. Notice that the tank is still 4BO green, but it has had snowfall accumulate on the nose of the tank. Source: Youtube.com
‘Giant’ was in a stony wooded sector of the front, quite unsuited to tank warfare, but the tanks committed themselves to the assault nonetheless. Contrary to standard practice, the KV was separated from the SMK and the T-100, and was assisting a company of T-28 tanks in the assault, following a tree line to the bunker. The T-100 and SMK were ordered to assist the infantry in crossing the stony open ground.
This attack did not go according to plan, and the T-100 and SMK were forced to call off the attack. Conflicting reports claim that the SMK did or did not get hit that first day. One account states that the vehicles were under intense machine-gun fire while supporting the attack, but remarkably did not suffer any hits. Finnish machine gunners were very well trained, and were likely concentrating their fire on the massed infantry accompanying the SMK.
Another combat report from AP Kunitsyn reads: ‘To test the fighting qualities of the new tanks, a rather difficult sector of the front was chosen. The front lines were between Summajärvi Lake and the non-freezing Sunasuo swamp. On the left of the height was an enemy camouflaged pillbox armed with 37-mm Bofors guns and machine guns. BOT (Armored Firing Points) covered two trenches, an anti-tank ditch and several rows of wire obstacles. Granite anti-tank racks stood in four rows. Together with the T-100 and KV tank, the SMK was to attack the enemy fortifications and capture the height at which the observation tower of the ‘Giant’ sat, which apparently served as a command and observation post. The actions of the three experimental tanks were observed by the commander of the North-West Front, commander of the 1st rank, S. K. Tymoshenko, commander of the Leningrad Military District, commander of the 2nd rank, K.A.
The hour of the attack arrived. A series of red rockets soared into the sky. The artillery preparatory bombardment was carried out in such a way as to not only suppress enemy defences, but also to break through passages in anti-tank barriers and minefields. With the last volleys of the artillery, the infantry went on the attack, and soon the tanks received orders to start moving forward. The commander of the SMK and the whole group, Senior Lieutenant Petin, buttoned down the hatch of the turret and, through an intercom, gave a command to the crew: “Forward!”
Ignatiev, the driver, clearly distinguished the road through the viewing gap. The tank, crushing trees and sprawling debris from thick, specially felled trunks, moved forward. Then, it broke through a number of wire barriers, crawled across the ditch and went to the granite dragon teeth.
With slow movements from side to side, Ignatiev began to swing and push the massive granite teeth. Finns methodically fired from anti-tank guns. Inside the tank was a terrible roar. The shells hit the armor with a terribly loud and painful noise, but the crew did not find any holes. The enemy intensified the fire, but not a single shell could penetrate the body of the vehicle.
It was extremely difficult for the commander and driver to control the tank under fire on such a difficult road. Smoke from firing the gun irritated the throats and eyes of the crewmen. But the crew continued to fight and boldly led the tank straight to the height of the enemy pillbox. Using the two turret guns, tankers fired at embrasures, and fired from machine guns.
Mechanic, AP P. Kunitsyn, one of the crew of the SMK recalled ‘The battle was terrible. Our tank, so thick-skinned, completely impenetrable. But we received a dozen and a half slug hits from the bunker, mostly small-caliber artillery.’
The two combat reports suggest that the SMK did in fact see intense action on the first day of fighting, but more was still to come.
The next day, 18th December 1939, the SMK, T-100, and KV were involved in still heavier fighting. This time, however, the SMK was involved in direct fighting. The three vehicles advanced down a road towards the bunker and were engaged directly with Finnish 37 mm Bofors guns. The SMK was hit at least a dozen times by 37 mm rounds, and successfully engaged Finnish positions, firing its main guns in anger. This, however, did not last long, as a shot from one of the 37mm guns jammed the main turret of the SMK, causing the crew of the main turret to become preoccupied with fixing this problem rather than fighting.
As the SMK traveled down the road, what the crew thought to be Finnish stores were stacked to one side of the road, and the SMK proceeded to roll over this equipment. It is claimed by the driver that he did not notice this debris, but the boxes and stores were hiding a Finnish anti-tank mine.
The mine detonated on the tank’s forward left track. The explosion was enormous, and ripped apart the SMK’s track, buckled the chassis, and broke the torsion bar suspension. The blast had also damaged the transmission, shut off electrics to the tank, and part of the floor plate had been knocked downwards.
One crewman, the driver, I.I. Ignatiev, was knocked unconscious by the blast, but was not seriously wounded.
In the T-100, EI Roshchin, a tester from the Kirov Plant, recalled that: ‘Going to the damaged SMK, our tanks (T-100 and KV) covered him with their armor. The T-100 stood in front and to the right, a KV was also in front, but a little to the left, so a triangular armored fortress was formed from three cars. In this configuration, we not only lasted for several hours, but also tried to put the SMK on the course, connecting the broken tracks. We were well-dressed in new coats, felt boots, fur helmets, mittens and the severe frost was easily tolerated, but the damage was too great – except for the tracks, the rollers suffered and the heavy machine could not be moved.’
Attempts were made to recover the SMK, but the track of the T-100 and SMK slipped on the heavy snow, and therefore the vehicle had to be abandoned. The crew of the SMK were evacuated by the T-100, which had more than enough room to accommodate the now 15 strong group in the tank.
Interestingly, D.A. Pavlov had been observing this engagement unfold. Upon the return of the SMK crew, they were personally de-briefed by Pavlov, and were given awards. But the question remained what to do with the wrecked SMK? The Soviets could not simply allow the Finns to capture the USSR’s newest heavy tank prototype.

Fate and Cancelation

On 20th December 1939, special orders were given by Pavlov to remove the SMK, and recover it to the Soviet lines. Seven T-28 tanks, two 45 mm guns, and an infantry battalion were given the task of recovering the SMK. This, however, was not successful. One T-28 was knocked out by artillery fire near the SMK, 43 infantrymen were injured, and two killed. Therefore, the SMK sat in the snow. Soviet crews had left many hatches open to the elements, and snow and water got inside the tank, further damaging the vehicle.
The vehicle sat where it was lost until February 1940. The Finns had shown little interest in the behemoth, though the vehicle was photographed. The T-28 lost near the SMK was harvested for spares, as the Finns had captured a number of T-28s in working condition, and were in the midst of pressing them into Finnish service.
While this was happening, the ABTU was finishing up the job of choosing a successor to the T-35. This was given to the KV tank, which had proved the best of the three vehicles tested. The designers of the T-100, Factory 185, tried for a while longer to have their design accepted, but to no avail. A second KV prototype was ordered in December, and KV-U0 returned to Kirov to have a new, ‘big turret’ fitted to hold a direct fire 152 mm support weapon.
As for the SMK prototype, the vehicle was cut up and scrapped after February 1940. Interestingly, the crew who served in the SMK were very fond of the vehicle, and spoke warmly of its survivability.

The last photograph of the SMK known to have been taken by Finnish authorities. A T-28 can be seen in front of the SMK, one of the vehicles sent to help recover it. Source: Aviarmor.com
The SMK was a vehicle too late to be practical, as its replacement was essentially designed in tandem with it. The flaws in multi-turreted tanks had been adequately displayed. Despite this, the SMK was a fine vehicle, being heavily armed and armored. Strictly following the ABTU’s specifications for a new multi-turreted heavy tank, the SMK was the vehicle the Red Army was looking for, but not the one it actually needed. However, the single-turreted version of the SMK, the KV, became one of the most important and influential vehicles in the history of armored warfare.
Interestingly, despite the flaws in multi-turreted tanks, engineers at the Kirov Plant drew up plans for a future KV tank with multiple turrets. This was the KV-5, with a 107 mm gun in a main turret, and a small sub-turret equipped with a DT-29 machine gun. This vehicle never left the drawing stage.
While the SMK was scrapped, the T-100 was converted into a heavy assault gun and renamed the T-100Y. This vehicle has survived to the present day, and resides at Patriot Park in Moscow. The KV prototype, KV-U0, was deployed on the Western Front (from the Soviet perspective) when the German attack came on 22nd June 1941, and was captured intact by German forces. It was likely scrapped by the Germans.
The Finns took at least one official photograph of the SMK, and handed it over to their allies. One such ally was Germany, which was busy categorizing Soviet tanks (both before and during WWII). The Germans were well aware of the T-35A. German categorisation called the cylindrical-turreted tanks T-35A, the conical-turreted tanks T-35B (though the Soviet T-35B was an entirely different product) and, interestingly, they called the SMK the ‘T-35C’. Despite the tanks having little in common beyond having more than one turret, the Germans thought that there was enough of a similarity to call it a T-35.
The official name for all T-35s was T-35A. This includes conical-turreted tanks. The T-35B was a version of the T-35 with a V2 diesel engine, which was planned but not produced.

The right side view of the SMK. The chassis has eight road wheels and four return rollers. This would be cut down two six road wheels and three return rollers on the KV tank. This was ultimately more successful and less cumbersome than the SMK’s layout. Source: TSAMO via Maxim Kolomiets

Sources

Tanks of the Winter War – Maxim Kolomiets
T-35 Heavy Tank. Land Dreadnought of the Red Army – Maxim Kolomiets
Aviarmor.com

SMK specifications

Dimensions (L-W-H) 8.75 x 3.4 x 3.25 m (28.7 x 11.1 x 10.9 ft)
Total weight, battle-ready 55 tons
Crew 7 – driver, engineer, 45 mm gunner, 45 mm loader, 76.2 mm gunner, 76.2 mm loader, commander
Propulsion GAM-34BT (ГАМ-34БТ) V-shaped 12-cylinder engine, 850 [email protected] rpm
Speed 35.5 km/h (22 mph)
Range 725 km
Armament 76.2 mm L-11 gun
Model 1934 45 mm gun
4 х 7.62 mm DT machine guns
12.7 mm DsHK model of 1938
Armor Frontal: 75 mm (2.95 in)
Side and rear: 55-60 mm (2.16- 2.3 in)
Turret side: 30 mm (1.81 in)
Bottom: 30 mm (1.81 in)
Top: 20 mm (0.7 in)
Production 1 prototype made


Illustration of the SMK Heavy Tank Prototype by Tank Encyclopedia’s own David Bocquelet.

Tanks Encyclopedia Magazine, #2

Tanks Encyclopedia Magazine, #2


The second issue of the Tank Encyclopedia magazine covers the fascinating history of armored fighting vehicles from their beginnings before the First World War up to this day! This issue covers vehicles such as the awe-inspiring rocket-firing German Sturmtiger, the Soviet SMK Heavy Tank, the construction of a replica Italian Fiat 2000 heavy tank and many more. It also contains a modeling section and a feature article from our friends at Plane Encyclopedia cover the Arado Ar 233 amphibious transport plane! All the articles are well researched by our excellent team of writers and are accompanied by beautiful illustrations and period photos. If you love tanks, this is the magazine for you!
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Categories
WW2 Soviet Prototypes

Dyrenkovs Armored Tractors (D-10, D-11, D-14)

USSR (1931) Armored Tractors – 1 prototype of each built

At the beginning of the 1930s in the USSR, several global interrelated processes were going on. These parallel processes had a severe impact on military effort and procurement.
Firstly, there was a need to re-equip and reform the army, in particular, the armored forces. The armored forces of the USSR mainly consisted of outdated tanks and armored cars, such as the British Mark V and Medium Mark A Whippet tanks or Garford-Putilov armored cars captured during the Civil War, and T-18 (MS-1, Maly Soprovozhdenya) tanks. These vehicles no longer met the needs of the tank units, The Red Army wanted a tank with a more powerful engine, better speed, maneuverability, ergonomics, and installed radios.
Secondly, the country’s leadership realized a serious setback in the industrial field. On July 15, 1929, the program of mechanization and motorization of the Red Army for the next 5 years was approved. By 1933, it was planned to have 3,500 active tanks in the army and another 2,000 in the mobilization reserve. At the same time, the RVS (Revolutsionniy Voenniy Sovet – Revolutionary Military Council, the supreme military authority of the Soviet Union) adopted a new system of auto-armor-tank-tractor armament, which was based on the modern requirements of combat and tactics.
When trying to implement the adopted plans for the development and production of new weapons and military equipment, the industry faced “enormous difficulties.”
Thirdly, both the production and the army suffered from a shortage of qualified personnel. New cadres (specially trained professionals) were not yet ready and did not have enough experience, and a significant part of the old and experienced specialists, for political reasons, were “cut off” from military service and leadership positions.
There were many different causes for rejecting specialists or young recruits “for reasons of political and moral inferiority”, such as affiliation to the “wrong ”class (bourgeoisie, clergy etc.) or professional backgrounds — service in the White Army or administration of the Russian Empire.
The military leadership, however, followed the global trends in the field of armaments and tactics and tried to keep up with them. At this time, new military theories were actively developed.
One of these theories was developed by the Soviet military theoretician and Marshal of the Soviet Union Mikhail Nikolayevich Tukhachevsky. According to that theory, simple and cheap armored tractors could be used as tanks of the 2nd and 3rd echelons (troops and armor of the 2nd and 3rd lines in a formation), even at the expense of reducing important combat characteristics.

“… we need to strive to have military tanks in numbers up to about one-third of the total, to perform special tasks, fight against anti-tank artillery, etc. The remaining tanks, usually advancing in the 2nd and 3rd echelons, can have somewhat lower speed, larger size, etc. And this means that such a tank can be an armored tractor, just as we have armored cars, trains and railcars, which will allow us to field armored tractors in huge masses.”

The Red Army required a large number of inexpensive, easy to manufacture and operate combat vehicles. The latter was especially important due to the acute personnel shortage – Soviet military theorists understood that the skills of the available manpower were not sufficient in the early 30s, and in the event of a major war, they would not have time to train qualified soldiers to man complex military equipment.
The Experimental Design Office of the Department of Mechanization and Motorization of the RKKA (UMM RKKA – Department of Mechanization and Motorization, Upravlenie Mekhanizacii I Motorizacii) was instructed to develop a “tractor tank”, like the American dual-purpose machine, the six-ton tractor Disston.
Most likely, the information about the Disston tanks was obtained from mass-media or during the so-called “Khalepsky Commission” visit to the USA. At that time, Nikolai Ivanovich Dyrenkov, a talented and extremely ambitious self-taught engineer, headed the Department of Mechanization and Motorization of the Red Army. Under his leadership, at the end of 1930, the development of so-called “surrogate tanks,” an infantry transporter and a number of other vehicles, began.

Development

The “Kommunar” tractor, a licensed version of the German tractor Hanomag WD50, was taken as the basis for the D-10 and D-14, and the American Caterpillar-60 tractor was taken as the basis for D-11.
The production of “Caterpillar-60” was planned to start in Chelyabinsk (a city east of the Ural Mountains, which became a very important transport hub and industrial center during 1930s). “Kommunars” were already in production in Kharkov.
The Department of Mechanization and Motorization of the Red Army was charged with building prototypes of so-called “surrogate tanks”: D-10, D-11, APC D-14 (“desantniy tank”). In Russian, the word “desant” is often used for troops which ride into the battle on top or inside the armored vehicles. Thus – “desantniy tank”. The same word is used for airborne troops – “vozdushno desantniye voyska”) and the D-15 “chemical tank”. All vehicles were created in the Moscow MOZEREZ plant (Moscow Railway Repair Plant, Moskovsky Zheleznodorozhny Remontny Zavod). By February 1931, they were ready.

Design

The design of all three vehicles was approximately the same: an engine was located in the front and, behind it, in the middle and aft part of the hull, there was a crew compartment, combined with a fighting compartment or compartment for troops. A fuel tank was also at the back.
On the roof of the fighting compartment there was a fixed commander’s cupola with viewing slots. Neither of the three vehicles had a rotating turret.

Armament

The D-10 and D-11 surrogate tanks were equipped with a 76.2 mm cannon on a pedestal mount as a primary weapon and two 7.62mm DT (Degtyaryov Tankovy) machine guns in the front and aft armor plates, as an auxiliary armament. Two more spare DT machine guns were stowed in the fighting compartment. There were two ball mounts for additional machine guns on each side armor plate. Worth noting is that the main gun mount was placed in the aft of the tank. In fact, this solution was the same as that of the Garford Putilov armored vehicles.
In the case of the Garford-Putilov, this decision was reasonable because the armored car had two driver positions and often went into battle ‘backwards’, but it was a significant flaw for the armored tractor, since it has to be turned around to fire the main gun.
According to some records, the ammunition did not fit into the tank and it was supposed to be carried on a towed trailer, but there is no information about the trailer itself. The D-14 APC was armed with two DT machine guns – one in the bow and one in the aft ball mounts.

Crew

The D-10 and D-11 tanks had a crew of 3 men – commander, driver, and gunner. D-14 APC had a crew of 2 men – driver and commander.
It is difficult to imagine how the engineers behind the design saw the distribution of crew duties between just two people. It can be assumed that firing was possible only after the vehicle stopped, so the driver or commander could take gunner positions.

Armored Hull

All three vehicles had riveted hulls made of rolled armor plates. The D-14 had three doors on each side of the hull used for the entrance and exit of the crew and dismounts. The D-10 had one door on each side; on the left side, the door was closer to the stern, on the right, to the aft. The D-11 had one door in the middle of each side.
A distinctive feature of all three armored vehicles was a massive armored engine in the front, which blocked visibility for the driver and made it difficult to fire a machine gun.

Engine

Propulsion was provided by a water-cooled four-cylinder, four-stroke engine with a carburetor and a vertical arrangement of cylinders. Kommunar 9GU and Kommunar 9EU had a 75 hp (55 kW) 4-cylinder petrol engine, and Caterpillar-60 had a 60 hp (45 kW) 4-cylinder gasoline engine.

Chassis and Suspension

All 3 vehicles used reinforced tractor chassis’ used as a basis with minimal changes. Transmissions were the same as on the original tractors. The D-10 and D-14 had a spring suspension with two springs for each bogie. The D-11 had a semi-rigid suspension.

Trials and Results

In 1931, all three vehicles were tested at the NIABT Test Site (Nauchno Ispytatelny Avtobronetankovy Poligon, Scientific armored vehicle proving ground in Kubinka, also NIABP). Most likely, the tests of all three vehicles (D-10, D-11 and D-14) were conducted in May-June 1931. This fact is confirmed by the document with the preliminary test results dated July 1931.
On July 18, 1931, the Scientific-Technical Committee of the UMM RKKA considered a report on the testing of three vehicles: a “Kommunar 9GU” armored tractor (D-10 tank), a “Kommunar 9EU” armored tractor-infantry carrier (D-14 APC) and an armored tractor “Caterpillar 60” (D-11 tank).

D-10 Tank

The total weight of the tank exceeded by 1.5 tonnes the original projection. As a result, the average speed and mobility decreased. Instead of the estimated speed of 7-8.5 km/h on roads and 5-6 km/h off-road, the tractor-tank showed 6-6.2 km/h on roads and only 3.2 km/h off-road. When the outside air temperature was above 15 °C and the radiator was closed, the water boiled after 1-1.5 hours of the engine being in use.
Obstacle overcoming tests were unsatisfactory. The tractor-tank coped with a 1.25 m wide and 1 m deep trench dug in sandy soil, which was no worse than MS-1 tank. But the vehicle did not cope with a 1.5 m wide trench. D-10 could cross, tear or crush barbed wire barriers only if the stakes did not fall between the tracks, because the bottom of the tank was not protected by armor.
The report also mentioned the fact that the engine could not be started from inside the tank and the absence of a vacuum apparatus for supplying fuel, both considered to be further negative aspects of the armored tractor. The D-10 had a ‘gravity fuel feed’, so if the tank got in an unfavorable position, for example, when crossing the trench, the fuel supply to the engine would be interrupted and the armored tractor would stop. It should be noted that the problem was old, and known since the days of the British Mark I Tank.
The following two problems were distinctive for most Soviet armored vehicles of the 1930s-40s. First, the tests showed difficulties with visibility due to the inconvenient location of the viewing slits. This applied, in particular, to the driver’s position. Secondly, it was noted that there was a lack of ventilation in the crew compartment.

Front view of a D-10 with the D-11 in the background. Source: RGVA

Right side view of the D-10. Source: Domestic armored vehicles. XX century

Left side of the D-10. Source: Domestic armored vehicles. XX century

D-14 Troop Carrier

The weight of the tank, as in the case of the D-10, was exceeded, this time by 2 tonnes. Due to the increased length of the hull, the load on the rear bogies was also increased; as a result, these bogies collapsed during the tests. Problems with the visibility and fuel supply were similar to those of the D-10.
There was also a problem with ventilation, although, in the case of an infantry carrier, it was more acute. According to the designer’s idea, the transporter was supposed to fit 18 riflemen (dismounts) with weapons, plus the crew, since the compartments for crew and dismounts were combined.
Poor ventilation made the conditions inside the APC such that after a few hours of being inside the vehicle, the soldiers and crew would be unable to perform their duties due to heat, cramped space and noise.
The engineer who designed the D-14 placed the doors for entering and exiting the armored tractor on the sides of the hull, with 3 on each side. The doors opened backward in relation to the nose of the vehicle. There were no hatches or doors in the stern. This decision made exiting the vehicle quite dangerous, as soldiers could not hide behind either the doors or the hull of the APC and would be exposed to enemy fire.
Subsequently, the number of troops carried decreased. Later Soviet experimental armored personnel carriers were designed for 14 (TR-1) and 15 riflemen (TR-4). For comparison, the crew of the French Lorraine 38L consisted of 12; driver, commander and 10 infantrymen – four in the troop compartment and another 6 in the armored trailer. It is noteworthy that the exit of the troops through the side hatches or doors returned to the Soviet APCs in the 60-70s, namely the BTR-60P and BTR-70.

Front view of the D-14. Source: Domestic armored vehicles. XX century

D-14 Prototype. Side doors and engine starting handle are clearly visible. Source: RGVA

Rear view of the D-14. Source: Domestic armored vehicles. XX century


Illustration of the D-10 Tank (armored tractor) based on the “Kommunar 9GU” tractor.


Illustration of the D-11 Tank (armored tractor) based on the “Caterpillar 60” tractor.


Illustration of the D-14 Troop Carrier (armored tractor) based on the “Kommunar 9EU” tractor.

These illustrations were produced by Andrei ‘Octo10’ Kirushkin, funded by our Patreon Campaign


D-11 Tank

As in the case with the D-10 and D-14, the weight of the vehicle was exceeded by 2.7 tonnes with similar consequences. The speed dropped to 4.7 km/h on roads and 3.9 km/h off-road. In addition to the familiar problems of D-10 and D-14 with fuel supply and engine overheating, the D-11 had its own unique ones.
According to test engineers, the armored hull was attached to the chassis extremely poorly. Firstly, the hull blocked access to the most important parts of the tractor, such as rear axle and gearbox. Secondly, during the tests, the armored hull of the tank tore off the bolts that attached it to the tractor and fell on the tracks.
Additional problems were reported: poor ventilation – during movement, “dust filled the crew compartment”. When trying to cross a trench, the tractor-tank “sticks the nose into the ground”.
It is not known whether this was a distinctive feature of this particular machine (which was the one based on the Caterpillar 60), or if it was also the case on the machines based on the “Kommunars”. In addition, D-11 has a reduced off-road capability in comparison with D-10 and D-14, because of the shorter base. The report noted a reduced cross-country capability and reduced mobility of this vehicle compared to the D-10 and D-14.

Left side view of the D-11. Source: Domestic armored vehicles. XX century

Test Results and Recommendations

On August 6, 1931, the test results were confirmed in another document, where conclusions and recommendations were presented.
General conclusions were as follows:

  1. “Surrogate tanks” were not suitable for clearing barbed wire fences due to unarmored bottom. Adding armor to the bottom meant increasing the weight, which means a decrease in the combat performance of already heavy and slow vehicles. In the second document, the general conclusion was much harsher: “nullifies the combat use of this type of armored vehicle”;
  2. The speed and maneuverability were considered insufficient, even for tanks of the 2nd to 3rd echelons. The chairman of the Scientific and Technological Committee UMM, Ivan Andrianovich Lebedev, noted that the average speed being “less than 4 km/h”;
  3. Suspension elements were destroyed or worn out due to the excessive weight of the vehicles;
  4. The artillery armament with which it was equipped was deemed unsatisfactory;

There was another important point that influenced the decision. It was considered that the “Kommunar” tractors surpassed the “Caterpillar-60” capabilities. But, firstly, “Kommunars” were produced by the KhPZ factory (Kharkov Locomotive Factory) in quantities that barely met the needs of the army in tractors for towage of artillery and other weapons. Secondly, the production at KhPZ was, in fact, custom-made. There was no exchangeability of parts even within the same series of machines.
The conclusion for Dyrenkov was disappointing: according to Lebedev, the main purpose of these tractors was towing artillery, therefore it was recommended to remove the armored hulls and convert the surrogate tanks D-10 and D-11 into self-propelled guns and test them.
In the case of the infantry transporter D-14, the UMM committee decided to retest it in order to “obtain more detailed data, both from the technical and from the tactical side.” Alterations included reduction of the troop compartment to 12 soldiers instead of 18. The rear part of the armored hull had to be partly cut off in order to reduce the load on the rear rollers.
In general, it was recommended to reduce the weight of the machine to 10 tons. To achieve this, it was proposed to remove or lighten individual armor plates. And, finally, to install an additional fuel tank, with the ability to pump fuel from the main fuel tank. Lebedev noted that “it is not possible to get a surrogate tank, even with reduced combat capabilities, without a major overhaul of the design.” In fact, it was easier to design a new tank.

Conclusion

Dyrenkov managed to create in 1931 armored vehicles that had the flaws of tanks of the Great War. The Red Army quit experiments with armored tractors but returned to them as an emergency measure in early 1941.
There was a plan to charge the faculty of mechanization and motorization of the Red Army to develop a personnel carrier on the chassis of the tank MM-1 (aka TMM-1, based on the Vickers Mk. E), as it was one of the most robust and common tanks of the Red Army. Further experiments with armored personnel carriers continued and the next attempt was the TR-1 (TR-26) transporter based on the T-26 tank. Nevertheless, the Red Army entered World War Two without any indigenous APC.
As for Dyrenkov and Tukhachevsky, they were both arrested and executed in 1937 during the “Great Purge”.

Specifications (D-10)

Total weight, battle ready ~ 12,000 Kg
Crew 3
Propulsion 4-cyl petrol, 75 hp (55 kW)
Maximum speed 6-6.2 km/h forward, 3.2 km/h reverse
Range 120 km on road
Armament 1 x 76-mm gun M1913 on Garford mount;
1 x 7.62-mm DT machine gun
Armor Front – 16 mm; Back – 16 mm; Sides – 11 mm, Top – 6 mm
Production 1

Specifications (D-14)

Total weight, battle ready ~ 12,500 Kg
Crew 2 + 18 passengers
Propulsion 75 hp (55 kW) engine
Maximum speed 6 km/h forward
Range 120 km on road
Armament 2 x 7.62-mm DT machine gun
Armor Front – 11 mm; Back – 11 mm; Sides – 11 mm, Top – 6 mm
Production 1

Specifications (D-11)

Total weight, battle ready ~ 13,250 Kg
Crew 3
Propulsion 60 hp engine
Maximum speed 4.7 km/h forward, 3.9 km/h background
Range 100 km on road
Armament 1 x 76-mm gun M1913 on Garford mount;
2 x 7.62-mm DT machine gun
Armor Front – 16 mm; Back – 11 mm; Sides – 11 mm, Top – 6 mm
Production 1

Sources

RGVA f. 31811 (Russian State Military Archive (Rossiiskii Gosudarstvenni Voennyi Arkhiv- RGVA)
Domestic armored vehicles. XX century: Scientific publication: In 4 volumes / Solyankin A.G., Pavlov M.V., Pavlov I.V., Zheltov I.G. / Vol 1. Domestic armored vehicles. 1905-1941 – M .: Exprint Publishing Center, LLC, 2002. – 344 pp. Ill., P. 61, pp. 88-89
Domestic Armored Vehicles 20th Century Vol 1 1905-1941 (Solyankin 2002)
Tukhachevsky / Boris Sokolov. – M: Molodaya Gvardiya, 2008. – 447 [1] s: il. – (Life of remarkable people: ser. Biogr .; issue. 1104)
Kirindas A.M. “Artillery tractor“ Comintern””, – Moscow: Yauza-Catalog, 2017
A.Bezugolny. “The Source of additional power of the Red Army …”, Moscow: ROSSPEN, 2016

Categories
WW2 Soviet Prototypes

T-35 Prototypes

USSR (1932)
Heavy Tank – 2 Prototype

The T-35A tank is one of history’s strangest tanks – often seen crawling across the Soviet inter-war era parade squares. This tank grabbed the hearts, souls, and imaginations of the Soviet people and foreign military attachés alike. It was one of the many proud achievements of Soviet industrialisation – its image appeared on posters, films, and even medals and awards!

Prototypes

In the late 1920s and early 1930s, the USSR was desperate for a modern army. After hard fighting during the Civil War (1918-1920), the vehicles of the Red Army were worn out and obsolete. These consisted mostly of obsolete Mark V heavy tanks and Medium Mark A Whippets.
Designing and mass-producing a new vehicle would help the fledgling Red Army set foot on the international stage again. It would also give Soviet engineering a fantastic opportunity to put its skills to the test, which were comparatively primitive to those of the USA and Great Britain in the late 1920s.
However, as Soviet engineering was still in its early stages of modernization, and as Soviet engineers had little to no experience designing tanks, it was decided to outsource Soviet tank designing to foreign sources. This came in three different types. The USSR would either pay for engineers to come to the Soviet Union and help build tanks, buy blueprints from foreign powers and visit tank factories or outright purchase foreign tanks wholesale and begin local manufacture.
In the heavy tank department, the German engineer Ernst Grotte was brought in from Germany, a country banned from tank development. Between 1929 and 1931, his design team came up with the TG tank. Grotte was assigned to the Leningrad AVO-5 design bureau.

TG Tank

The TG tank was a large tank with two independent tiers of armament. The lower elliptical turret was equipped with an A-19 76.2mm (3 inch) gun, and a rotating turret mounted on top of the first one which was fitted with a 37mm (1.46 inch) PS-2 gun. The suspension consisted of coiled springs, and each side of the vehicle had five large diameter road wheels.
The TG tank also had three water-cooled 7.62mm (0.3 inches) Maxim machine guns, one on either side of the hull and one at the rear of the machine. The vehicle weighed 20 tonnes, The tank was powered by the M-6 Aero-engine and could reach a maximum of 35 kilometers per hour (22 mph). The TG had a crew of 5.
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The TG Tank during trials. The turret ring for the main turret broke, therefore tests were conducted with the turret permanently facing forward. Source: Military Images
The vehicle was tested in April 1931 and was quite successful, displaying good cross-country capabilities, relatively good speed, and reliability. A noted flaw though, was that the fighting compartment of the vehicle was very cramped.
However, the TG project was dropped, not due to the vehicle’s performance, as this was better than other Soviet prototypes at the same time, but rather due to costs. It would cost almost 1,500,000 roubles to manufacture a single such tank, money better spent on manufacturing up to twenty-five BT-2 fast tanks.
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The TG tank incorporated many modern ideas, however, it was an inherently flawed vehicle. Source: panzernet
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The TG tank in 1940. Nothing more than a display piece at the Polygon near moscow. Source: panzernet

Unrelated to the Independent

Some allege that the T-35 was inspired by the British A1E1 Independent tank, but Soviet-era sources claim that the A1E1 had no influence on the design, despite Soviet knowledge of the vehicle. Indeed, apart from the layout of the turrets, the T-35 and A1E1 are very different machines.

The British A1E1 independent tank. Even a quick inspection will reveal that the machine is vastly different to even the prototype T-35-1 and T-35-2. Illustration by David Bocquelet.
Soviet engineers were given the opportunity to inspect the A1E1 Independent tank when advisors from the USSR visited the Vickers factory in 1930. However, they found the same flaws in the machine as the British did, i.e. that the tank was too long and too thin, and the tank’s sides were prone to warping under the tension of the tracks.

T-35 specification

Dimensions (L-w-h) Unknown
Total weight, battle ready 35 Tons
Crew 9
Propulsion M-6/ M-17L Aero engine
Armament 1x Ps-3 76.2mm, 2x Ps-1 37mm, 4x 7.62mm
Total production 2

Links, Resources & Further Reading

Fallen Giants: The Combat Debut of the T-35A Tank – Francis Pulham
Land Battleship: The Russian T-35 Heavy Tank – Maxim Kolomiets & Jim Kinnear
aviarmour.ru
ww2 soviet armour
ww2 Soviet Tanks Poster

T-35-1 and T-35-2

A new heavy tank prototype was designed in early 1932, designated ‘T-35-1’. It was produced at the Kharkov Locomotive and Tractor Works (KhTZ). This first prototype had six pairs of road wheels arranged with two pairs of road wheels per bogie. Each bogie was fitted with coiled spring suspension comprised of two pairs of springs. The name T-35 comes from the Red Army requirement for a 35-ton tank.
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Both the T-35-1 and T-35-2 were paraded in 1933 on palace square. Notice the round turret roof of the T-35-1. Source: pinimg.com
All the sub-turrets of the prototype were of the same design and shape regardless of armaments. Two of the turrets were equipped with the 37 mm PS-2 guns and the other two having DT-29 machine guns. When facing forward and aft of the tank, the 37 mm turrets were on the right, while the machine gun turrets were on the left. The main turret was fitted with a 76.2 mm PS-3 gun and another machine-gun in a ball-mount to the right of the gun. It was welded with distinctive curved roof and rested on an armored pedestal.
The tank had two armored skirts on either side to protect the suspension. However, rather foolishly, the skirts of the first prototype had no access ports and there was no way to access the suspension without pulling the skirts apart. The tank was powered by the M-6 aircraft engine, with the drive wheel at the rear. The tracks ran on top of 6 return rollers that were almost two meters above the ground.
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The T-35-1 turret was removed at some point when the tank was dismantled. Here it sits at the Polygon in 1940. Source: Sergey Lotarev
The prototypes had crews of 9, a driver, engineer/ hull machine gunner, a single crew member in each of the four small turrets, and three crew in the main turret. The driver and engineer were equipped with dome-type escape hatches on the front hull roof.
This prototype was evaluated in mid-1932 before a second prototype was ordered. The second prototype was outwardly similar, with the exception of the addition of access ports in the skirts. These were square shaped and gave all-important access to the bogies for maintenance. In addition, the main turret relinquished the round roof.
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The T-35-2 can be harder to distinguish from production T-35s, however inspection of the drivers compartment with the hull machine gun and the escape hatches clearly reveals its origin. Source: www.battlefield.ru
The powerplant of the second prototype was changed to the new M-17L Aero Engine. This was the Soviet copy of the BMW VI Aero engine. Accordingly, this prototype was called the ‘T-35-2’.
These T-35 prototypes were both evaluated but were not accepted for Red Army service. This was due to a new design buro designing a similar, yet superior machine.
The OKMO of Kharkov, in parallel with the T-35-2, had designed the T-35A prototype. Similarly to how the T-37 and T-37A were different vehicles with similar names, the two tanks shared similarities but were, by and large, different vehicles.

Visual Identification Guide

The two T-35 prototypes are discernable from production T-35A tanks through a multitude of factors. The main way of identification is by the placement of the exhaust pipes lengthwise on the rearmost fenders. Production T-35As had their exhaust lying sideways on the central hull, and in later tanks, this was moved under armor.
The turrets too are different. The main turret of the T-35-1 had a distinctive round roof, and the T-35-2 is missing much of the exterior detail that production T-35As had. The main gun in the main turret was also a PS-3 76.2mm gun rather than the KT-28 76.2mm gun of production tanks.
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The front of the T-35-1. Notice the two driver’s positions. Source: Land Battleship T-35
The sub turrets on the two prototype tanks were all identical to each other, whereas production T-35s 45mm gun turrets were larger than the machine gun turrets, and were cylindrical in shape.
Hulls too were very different, with the prototype T-35-1 and T-35-2 having only six road wheels per side, whereas production tanks had eight road wheels. The entire nose of the vehicle was different, with the two prototypes having round bulbous escape hatches for the driver and engineer. Additionally, there was a hull-mounted machine gun position on the prototypes absent from production tanks.
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One of the production T-35A’s. Notice the vast differences between this machine and the prototypes. Source: Land Battleship T-35

Conclusion

The two T-35 prototypes, while sharing the name and basic layout with the T-35A, was, in reality, an entirely different machine. It is clear inspecting the dimensions and the armaments that the prototypes were inferior in almost every way to the production T-35As.
While a useful jumping-off point, these prototypes were technical failures. The production tanks heavily differed from these prototypes, so much so that pre-Glasnost western sources called these prototypes “T-32”. This is, of course, wrong.


T-22 Tank Grotte prototype


T-35-1 prototype
Both Illustrations by Tank Encyclopedia’s own David Bocquelet

Combat Debut T35A
Fallen Giants: The Combat Debut of the T-35A Tank

By Francis Pulham

The Soviet T-35A is the only five-turreted tank in history to enter production. With a long and proud service history on Soviet parade grounds, the T-35A was forced to adapt to the modern battlefield when the Second World War broke out. Outclassed and outdated, the T-35A tried to hold its own against the German invaders to no avail. For the first time, actual battlefield photographs have been cross-referenced with maps and documents to bring about the most complete look at the T-35A in the Second World War to date.

Buy this book on Amazon!

Categories
WW2 Soviet Prototypes

ISU High Power Gun Projects

Soviet Union USSR (1944-1945)
Heavy Tank Destroyers – 5 prototypes

Dedicated Beast Slayers

In mid-1944, the Red Army recognized that it might need tanks that could consistently and reliably destroy the Wehrmacht’s most well-armored tanks. The Red Army fielded few tanks that could destroy the King Tiger, Elefant, and Jagdtiger reliably from medium-long ranges. Although it is true that the ISU-122, ISU-122s, ISU-152, and IS-2 were capable of destroying German heavy tanks, their combat results were not consistent enough. As a result, starting in June of 1944, five “BM” (“High Power” – Russian: “высокой мощности”) guns were developed for the ISU chassis. The resulting vehicles were: Object 243 (ISU-122-1 with the 122mm BL-9 gun), Object 246 (ISU-152-1 with the 152mm BL-8 gun), Object 247 (ISU-152-2 with the 152mm BL-10 gun), Object 250 (ISU-130 with the 130mm S-26 gun), and Object 251 (ISU-122-3 with the 122mm S-26-1 gun). More gun projects were being developed at this time, but no others appeared to be mounted onto a chassis. The guns proved capable, on paper, of destroying tanks such as the Jagdtiger, but testing showed that they were simply not practical. Moreover, these projects took well over a year to refine, and seeing as though the war ended before they were complete, they were all dropped.

A table with comparative statistics is provided at the bottom of the article.

Context: Soviet guns against German armor

Mythbusting: The SU-152 and ISU-152 were “Beast Killers”
Soviet wartime propaganda suggested that the SU-152 and ISU-152 (SU being based on the KV chassis, ISU being based on the IS chassis) were “Beast-Killers” because they could destroy Panthers, Tigers, and Elefants. The ISU-152’s 152mm ML-20S howitzer was, indeed, capable of destroying heavy German armor, but this required a direct hit with a High Explosive (HE) shell. Such a direct hit could do one of three things to disable the tank: destroy the vehicle’s drive systems, kill its crew, or blow the turret / casemate / hull open (or even clean off, in the case of turrets). Armor Piercing (AP) and Concrete Piercing shells were developed, but these were expensive and complicated to make, hardly more effective than HE rounds, and thus were scarcely supplied – even at Kursk! However, the ISU-152 was not a dedicated tank destroyer – it was an assault gun designed for bunker busting and indirect fire. Needless to say, using an assault gun as a tank destroyer was risky business.
Firstly, the gun would need to be fired at short ranges against enemy tanks. This is because the ML-20S was a fairly low velocity howitzer, which would simply not be accurate enough to engage tanks from distances. Consider also that the vehicle had a maximum of 90 mm of armor, which meant that it whilst it was adequately protected from some German guns at long ranges, it simply was not thick enough to protect the vehicle in the short ranges it would need to operate in as a tank destroyer. For example, the 7.5 cm KwK 40 L/48, as mounted on StuGs, Panzer IVs, and Jagdpanzers, could penetrate 97 mm of armor at 500 m, and 87 mm of armor at 1000 m, at 30 degrees (the ISU-152 casemate was barely sloped at all). Also consider that the vehicle was simply not mobile enough to be engaging more nimble German tanks, and could probably be outmaneuvered anyway.
Yet another major issue of using the ISU-152 as a tank destroyer was that it could only manage 1-3 rounds per minute (depending if it had one or two loaders, and how experienced they were). This meant that in any type of ‘duel’, the ISU-152 would not only need to fire first, but also guarantee a hit, or practically any opposing German tank could get numerous shots off against it – as mentioned early, likely knock-out blows. Having said this, it did not seem to be a consideration taken into account when making the “BM” projects, as the guns all had equally as poor rates of fire.
In conclusion, the ISU-152 did not live up to its legendary name. Other Soviet field guns and tank destroyers had somewhat better results compared to the ISU-152, although the results were still not quite satisfactory.
Mythbusting: The 122 mm A-19S and D-25T / S were sufficient
It is a commonly held belief that the 122 mm D-25T / S and A-19S were sufficient at destroying the heaviest German armor. This belief is somewhat problematic, given the weight of the evidence.
According to a Wa Preuf 1 (a Wehrmacht weapons research facility) report from October 5th, 1944, the 122mm A-19 (the A-19S being used on the ISU-122, the latest Soviet SPG at that time) could not penetrate the upper glacis of a Panther. However, it could penetrate the lower glacis from a distance of up to 100 m, the mantlet from 500 m, and the side of the turret from 1500m. This was still somewhat wanting, as the Red Army would prefer to engage such tanks from longer ranges, to prevent heavy losses of their own tanks.
The improved 122mm D-25T (which was used on the IS-2, the D-25S was essentially the same, and was used on the ISU-122S) seems to have fared much better against German armor. Testing of the gun on the IS-2 platform in Kubinka in 1944 suggests that a King Tiger’s turret (likely the side) could be penetrated from up to 1000-1500m. The welds of front hull seams could also be penetrated from 500-600m. Whilst these penetration statistics might make the D-25T sound more promising, they must be taken with some caveats.
Firstly, to score such hits would require a very skilled and very experienced gunner – especially to score a hit on the turret from a range of up to 1500m. Secondly, similar to the ML-20S, the D-25T could only manage up to 3 rounds per minute. Thirdly, the validity of these statistics has been called into question, because they come from Soviet sources. In the past, these statistics were often exaggerated for propaganda purposes. Finally, the very fact that the ISU “BM” projects were put into production suggests that the Soviets knew that the D-25T would not give consistently reliable results in AT duties.
Whilst, indeed, the D-25T was, in theory, capable of destroying the heaviest German armor, it was perhaps not as reliable as it needed to be in the field. Of course, it is true that penetrations were not required to disable the tank or kill the crew (both in the case of the ML-20S and D-25T), but one could not simply rely on non-penetrating hits to, in some manner, disable the tank.
As a result of these relatively unsatisfactory Soviet AT capabilities against the Wehrmacht’s heaviest tanks, in June 1944, Zavod Nr. 100 began developing new, high velocity 122 mm, 130 mm, and 152 mm guns to be mounted on the ISU (and perhaps IS and KV) chassis.

Object 243 (ISU-122-1)

Object 243 (ISU-122-1) with the 122mm BL-9
Object 243 (ISU-122-1) with the 122 mm BL-9. This vehicle is distinguishable as its gun has no muzzle brake, and looks like an elongated A-19S. However, the gun replicator has been angled (see the rectangular plate on the mantlet below the gun), unlike a regular ISU-122.

  • The Object 243 featured the 122 mm BL-9 gun – one of the infamous BL guns made at OKB-172. The vehicle can be distinguished by its gun and mantlet. The gun essentially looked like a longer version of the A-19S. The mantlet also had some tweaking to fit the longer and heavier gun – most notably, the tip of the gun replicator has been angled to one side (just below the gun).
  • It could penetrate 204 mm of armor at 1000 m, with 2 rounds per minute.
  • The gun’s muzzle velocity was 950 m/s with an 11.9kg AP shell.
  • It had a range of 10,700 m, compared to the 6000 m range of the 152 mm ML-20S of the ISU-152 and SU-152.
  • It could carry 20 AP rounds, the same as the ISU-152.
  • Like the other “BM” guns, the BL-9 was likely too powerful for its mountings, which caused mechanical issues.

Object 246 (ISU-152-1)

Object 246 (ISU-152-1) with the 152 mm BL-8
Object 246 (ISU-152-1) with the 152 mm BL-8. This vehicle is distinguishable by its slightly longer gun than the Object 247 (15 cm, or 5.9 inches), but the same muzzle brake, and its unchanged gun replicator.

  • The Object 246 featured the 152 mm BL-8 gun. This vehicle can be distinguished by its distinctive muzzle brake, and unaltered gun replicator.
  • It could reportedly penetrate 203 mm of armor at 90 degrees from up to 2000 m away (dubious) 1, with 3 rounds per minute.
  • The gun had a muzzle velocity of 850 m/s with a 43.56 kg HE shell.
  • It had a maximum range of 18,500 m.
  • It could carry 21 rounds.
  • Whilst these results sound excellent, trials in December 1944 showed that the crew found operating the gun difficult, the muzzle brake and breech block were unreliable, and the barrel strength and angle of horizontal guidance were unsatisfactory. Consider also that the very long gun would limit the maneuverability of the vehicle, much like the D-25S on the ISU-122S limited its maneuverability. As a result, the 152mm BL-10 was developed…

Object 247 (ISU-152-2)

Object 247 (ISU-152-2) with the 152 mm BL-10
Object 247 (ISU-152-2) with the 152 mm BL-10. This vehicle is distinguishable by the length of its barrel (it was slightly shorter compared to the BL-8), its muzzle brake, and its altered gun replicator.

  • The Object 247 fitted the 152 mm BL-10 gun, an improvement of the BL-8. This vehicle can be distinguished by its muzzle brake and slightly altered gun mantlet, whereby the rectangular tip of the gun replicating system had been angled, unlike the original ISU mantlet.
  • It could penetrate 205 mm of armor from 1000 m.
  • The gun had a muzzle velocity of 851 m/s with a 43.56 kg HE shell.
  • It had a maximum range of 17,000 m.
  • It could carry 20 HE shells.
  • Testing revealed that barrel integrity and angle of horizontal guidance were poor.
  • It was eventually deemed that there was no need for this work to continue, mostly because the war was over, and there was no need to combat heavily armored German vehicles.
  • Consider also, that whilst the barrel length was a little shorter than the BL-8, it, too, would still suffer from maneuverability issues as a result.

Object 250 (ISU-130)

Object 250 (ISU-130) with the 130 mm S-26
Object 250 (ISU-130) with the 130 mm S-26. This vehicle is distinguishable by its unique muzzle brake.

  • The Object 250 (ISU-130) was built in autumn, 1944 and featured a 130 mm (5.12 in) S-26 gun. This gun is sometimes referred to as a naval gun, but this is not entirely accurate – the S-26 derived from a naval gun and featured a rectangular muzzle brake and horizontal wedges.
  • It could penetrate 196 mm of armor from 1000 m.
  • It had a muzzle velocity of 702 m/s, firing a 33.4kg HE shell, with 1.5-2.5 rounds per minute.
  • It had a range of 15,000 m.
  • It could carry 25 shells, which were smaller than 152mm shells, meaning that it provided similar ballistic results to the 152mm BM guns, but could carry more shells.
  • In October 1944, the ISU-130 underwent factory trials, and the following month, trials were held at the Polygon.
  • A major concern came from the caliber – 130mm. The issue was that the army would have to make special arrangements for the 130mm naval shells to be supplied to the army, and thus it was decided that a gun using current army-issue 122mm or 152mm would be preferable.
  • Testing of the ISU-130 ended in 1945, and the gun was sent to the TaSKB for completion, but the war was over, and the project was disbanded.
  • The ISU-130 is currently preserved at the Kubinka Tank Museum.

The ISU-130 preserved at Kubinka.
The ISU-130 preserved at Kubinka.

Object 251 (ISU-122-3)

Object 251 (ISU-122-3) with the 122 mm S-26-1.
Object 251 (ISU-122-3) with the 122 mm S-26-1. This vehicle is distinguishable by its round gun mantlet and its unique cylindrical muzzle brake.

  • The Object 251 was derived from the ISU-130. It featured essentially a 122 mm version of the 130 mm S-26, which was designated the S-26-1. It had a round muzzle brake, different components, but the mantlet was the same shape.
  • It could penetrate 204 mm of armor from 1000 m.
  • It had very similar ballistics to the BL-9, but had a muzzle velocity of 1000 m/s, firing a 25kg shell.
  • It could fire a disappointing 1.5-1.8 rounds per minute.
  • It underwent field tests in November 1944, but according to sources, something (probably the mantlet and / or gun mechanism), was simply not strong enough to withstand firing the gun.
  • The gun project was totally completed in June 1945, but was abandoned due to the war’s end.
  • (Note that the ISU-122-2 was the ISU-122S with the 122 mm D-25S, hence the skip from ISU-122-1 to ISU-122-3).

Conclusion

The “ISU High Powered Gun Projects” were, in many respects, a failure. True, the guns were incredibly potent, particularly in the case of the S-26-1, which could penetrate 204 mm from 1000 m. They also had a very long range, only limited by the elevation of the ISU mantlet. However, they were simply not practical and mechanically reliable enough for their intended purpose, which was to knock out the thickest armored Wehrmacht tanks consistently, and from long ranges.
Even if the vehicles were put into serial production, how often these tanks would face off with the most heavily armored vehicles of the Wehrmacht is questionable. With Jagdtigers, King Tigers, and Ferdinands being so rare, the war was more likely to have ended before the ISU High Powered Projects saw combat with the vehicles they were designed to destroy. What had ultimately put the nail in the coffin for these guns was that the war had ended, and they were no longer necessary.

Sidenote: Designations and identification through photos

In the writing of this article, it has been exceptionally difficult to pin down which photos correspond to which project. Indeed, some sources only mention four (in some cases, only three) High Powered Gun Project vehicles. It has been the author’s conclusion that there were five such High Powered Gun Projects mounted onto ISU chassis, as outlined in Solyankin’s book “Советские тяжелые самоходные артиллерийские установки 1941-45″. Most online sources, particularly non-Russian language sources, are incredibly inaccurate. Gun statistics were mostly provided by a Soviet data set as provided by Tankarchives.blogspot. However, these statistics sometimes differ with Solyankin.

Notes:

1 – Note 1 – Most data has been obtained from this Soviet data set. However, certain statistics have not been given and have been obtained from alternative (potentially dubious) sources. Where necessary, statistics provided by Solyankin have been used, but these are questionable.
2 – Note 2 – Experienced crews were able to load much faster. Consider that the BM guns were likely tested by experts in test ground conditions, thus likely making their rounds per minute data higher than would be in the field, by more typical tank crews.
3 – Note 3 – Obtaining the ISU-122S’ ammo capacity has been difficult. It is reported that with a crew of four, instead of five (IE, one loader instead of two), then ammo capacity was increased, but the only given figure is 30, presumably with two loaders.
Sources:
Germany’s Panther Tank: The Quest for Combat Supremacy”, by Thomas Jentz
Sturmgeschutz & Its Variants”, by Walter J. Spielberger
“Советские тяжелые самоходные артиллерийские установки 1941-45”, by A.G. Solyankin
battlefield.ru
battlefield.ru (second page)
forum.axishistory.com
tankarchives.blogspot
tankarchives.blogspot (second page)
tankarchives.blogspot (third page)
armchairgeneral.com forums
WW2 AT Penetrations.pdf
alternatewars.com
alternatewars.com (second page)
ftr.wot-news.com
3.bp.blogspot

BL-9

BL-8

BL-10

S-26

S-26-1

ML-20S

D-25S

12.8cm PaK 44 L/55

Chassis Object 243 Object 246 Object 247 Object 250 Object 251 ISU-152, SU-152 ISU-122S Jagdtiger
Caliber 122 mm 152 mm 152 mm 130 mm 122 mm 152 mm 122 mm 128 mm
[email protected] deg 204 mm from 1000 m
157 mm from 1500 m
155 mm from 2000 m
203 mm1
from 2000 m (Dubious)
205 mm from 1000 m
202 mm from 1500 m
160 mm from 2000 m
196 mm from 1000 m
184 mm from 1500 m
156 mm from 2000 m
204 mm from 1000 m
157 mm from 1500 m
156 mm from 2000 m
125 mm from 500 m 147 mm from 500 m
138 mm from 1000 m
and 129 mm from 2000 m
200 mm from 1000 m
30 degree angle
PzGr.43 shell
Rounds per Minute 2 3 1 No data 1 1.5-2.25 1.5-1.8 1-3 2
(crew dependent)
1-3 2,3
(crew dependent)
2
Muzzle velocity 950m/s1(AP)
700 m/s (HE)
850 m/s (presumably HE) 1 826 m/s (AP)
851 m/s (HE)
898 m/s (AP)
702 m/s (HE)
1000 m/s (AP and HE) 600 m/s (HE) 800 m/s (HE) 950 m/s (AP)
Range 10,700 m 18,500 m 1 17,000 m 15,000 m 1 15,000 m 1 6000 m 5000 m 24,410 m
Shell Weight and Type 11.9kg AP 43.56kg HE 43.56kg HE 33.4kg HE 25kg HE 43.56kg HE 25kg HE 28kg HE
28.3kg AP
Ammo Capacity 20 21 1 20 25 24 20
(ISU-152)
30 1, 3 38-40
Overall length, chassis included 11.15 m (36.58 ft) 11.82 m (38.78 ft) 11.67 m (38.29 ft) 11.42 m (37.47 ft) 11.26 m (36.94 ft) 9.18 m (30.12 ft) 9.85 m (32.32 ft) 10.65 m (34.94 ft)


Illustration of the Object 247/ISU-152-2 armed with the 152mm BL-10 gun by Tank Encyclopedia’s own David Bocquelet

Categories
WW2 Soviet Prototypes

Matilda II Mk.IV with ZiS-5 76mm

USSR (1941)
Infantry Tank – 1 Prototype Built

In the early stages of WWII, Great Britain started a lend-lease relationship with the Soviet Union. Along with the Churchill III, Tetrarch, Valentine and Universal Carrier, the famous Queen of the Desert Matilda II soon found itself in the USSR.

Between 1941 and 1943, some 1084 Matildas were shipped to the Soviet Union. Only 918 were ever received by the Red Army, however. It is suggested that the others never made it to the end of the famous Arctic Convoys. This is one-third of the entire 2987 vehicle production run of the Matilda.

The Matilda equipped with the 76mm ZiS-5 gun . Photo: pinterest

Fighting Under the Red Flag

The Matilda IIs that found their way to the USSR were mostly Mk.IIIs and Mk.IVs, with Leyland diesel engines. Diesel being the preferred fuel of the Soviets. The Soviets identified the Matilda as the “British Mk.2”. The 170th and 171st Tank Battalions of the South-Western and Kalininsk fronts were the first units to receive the tank. At the time of the Battle of Moscow, their first action under the Soviet flag, only 145 Matildas had been received. Along with the Valentine, the Matildas only made up 2 percent of all Soviet armor used. The 170th only had 13 of them at the time.

Matilda’s tanks of the Soviet 5th Mechanized Corps, 68th Army. Photo: Osprey Publishing

Soviet crews fell in love with the Matilda, however, and up until 1942 they deemed it “the toughest tank on the western front”. To the Soviets, of course, the German front was the “Western” front. The only thing they didn’t like were the tracks, that were ill-suited to icy conditions. The tank fought on several fronts under Soviet use, mostly on Western Front, but also at North Caucasian Front and Bryansk Front until at least early 1944. In December 1943, the 5th Mechanized Corps of the 68th Army, fighting on the Western front, still had 79 fully operational Matildas.

Soviet Modification

The Red Army soon realized that the standard 40mm 2 pounder cannon of the Matilda was becoming less and less effective against German armor. As such, in December 1941 at design office number 92, Vasiliy Grabin, the famous designer of the ZiS-3 gun, made plans to mount the Soviet’s own 76mm tank gun M1941 ZiS-5 (76-мм танковая пушка обр. 1941 г. ЗиС-5), on the Matilda.

The ZiS-5/F-96 gun used on the Matilda. Photo: warspot.ru

This was the same gun found on early war KV-1s. It was re-designated as F-96 for the project. The weapon was a substantial improvement over the 40mm/2-pounder. The 76mm shell could penetrate up to 61mm of armor at 1,000 meters and could fire numerous types of ammunition including HE-F (High Explosive – Fragmentation), APCR (Armor Piercing Composite Rigid) and APHE (Armor Piercing High Explosive). The gun could elevate to roughly 20 degrees, but could only depress 2 degrees. 120 guns were originally put-by for the project, however this was later cut down to only 40.

Cramped

Just one Matilda, still having its British War Department (W.D) numeral markings, was experimented on. Extensive modifications of the turret were implemented to allow the larger gun to fit, requiring a complete redesign of the mantlet. The new mantlet was based on the KV-1’s, and to grant a little extra room inside the turret, a gasket roughly an inch thick was placed in-between the mantlet and turret face.

The turret of the Matilda was cramped to begin with, so one can only imagine how much more uncomfortable it would’ve been with the 76mm inserted. It is unknown as to whether this Matilda would’ve kept the same amount of crew as the stanard tank. If so, the loading and general operating of the gun would likely have been an awkward task.

Another view from the front shows how disproportionate the mantlet looks to the rest of the Vehicle. Phot: ftr.wot-news.com

Fate

In January of 1942, the modified tank was sent to Moscow for testing. Come March 1943, the Commissar for Tank Industry, V. Malysheva and Commissar for weapons D. Ustinovu contacted the design team in a letter basically telling them the project was canceled as the guns were needed for the USSR’s own tanks, which were rolling off the assembly line by the battalion load. Because of this, the project was canceled with just the one prototype built. The prototype was likely scrapped soon after. It is possible that the component parts were put back into circulation. The guns may have been re-installed on their respective vehicles with the F-96 going back to a KV, and the 2-Pounder going back onto the Matilda hull.

There is, however, and unverified German intelligence report that the 36th and 37th Tank Brigade were equipped with 76mm armed Matildas. There is no concrete evidence to back this up though. It may be that the tanks were mistaken for Matilda CS versions, of which there was 130 sent to the Soviets.

This image shows the gun at maximum elevation. Photo: warspot.ru

The Soviets were not the first to attempt an up-gunning of the vehicle. As well as the experiments on using the Littlejohn adapter for the 2-pounder, the British army attempted mounting the QF 6 pounder gun in a new turret taken from the A27 Cromwell. Like the Russian concept, this too was scrapped with one prototype built.



The ZiS-5 armed Matilda. This illustration was produced by Tank Encyclopedia’s own by David Bocquelet.

Matilda II specifications

Dimensions 18 ft 9.4 in x 8 ft 3 in x 8 ft 7 in (5.72 x 2.51 x 2.61 m)
Total weight, loaded 25.5 tons (25.6 tonnes)
Crew 4 (driver, gunner, loader, commander)
Propulsion 2x Leyland E148 & E149 straight 6-cylinder water cooled diesel 95 hp engine
Max. Road Speed 15 mph (24.1 km/h)
Operational Road Range 50 miles (807 km)
Armament 76mm ZiS-5 Gun
Armor 15 mm to 78 mm (0.59-3.14 in)
Total production 1 prototype
Data source Infantry Tank Mark II Specifications, by J.S. DODD The Vulcan Foundry Ltd, Locomotive Works, August 1940

Sources

Infantry Tank Mark IIA* Specifications, The Vulcan Foundary Ltd by designer Sir John Dodd August 1940
Infantry Tank Mark II manual, War Department
Osprey Publishing, New Vanguard #8, Matilda Infantry Tank 1938-45

Soviet Matildas on FTR
Matilda Mk.IV on Panzernet.net (Czech)
A live journal entry on the Matilda IV (Russian).
An article by Yuri Pasholok on Warspot.ru.
Osprey Publishing, New Vanguard #247: Soviet Lend-Lease Tanks of World War II