Cold War Soviet Prototypes

K-91 SPG

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

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


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

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


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

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

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

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


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

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

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

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


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

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

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


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


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


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

Object 268 Version 4, on December 18, 1952.

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

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

K-91 SPG specifications

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


Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965
Yuri Pasholok on the Soviet STG – Status Report (

Cold War Soviet Prototypes

K-91 (Rear mounted turret)

Heavy tank – Soviet Union
(1949) Blueprints only

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


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

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


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

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


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

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

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


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

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

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

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

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


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

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


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

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

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


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

Other K-91s

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


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

K-91 rear-mounted turret specifications

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


Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965
Yuri Pasholok on the Soviet STG – Status Report (

Cold War Soviet Prototypes

K-91 (Front mounted turret)

Soviet Union (1949) Heavy tank – Blueprints only

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


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

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

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

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


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


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

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

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


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

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

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


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


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

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


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

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

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

Other variants

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

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

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


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

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

K-91 (front turret) specifications

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


Technic and Weapons No. 9, 2013, M.V. Pavlov, I.V. Pavlov Domestic armored vehicles of 1945-1965
Yuri Pasholok on the Soviet STG – Status Report (

Cold War Soviet Prototypes

Gremyakin’s Medium Tank (STG)

Soviet Medium tank (1953) Medium Tank – Blueprints only

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


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

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

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

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

The requirements were to be:

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

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

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

Layout & Design

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

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

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

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

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

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


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

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

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


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

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

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

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

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

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


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

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


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


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

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

Torsion springs used on the Italian CV38.
Source: Unknown

Fate: Failure

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

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

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

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

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

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

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


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

STG specifications

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


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:

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.


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.


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


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.

Heavy SPGs 1941-1945, Soliankin, Pavlov, Palov, Zheltov
Zveroboy, Mikhail Baryatinsky
Heavy SPG, A.V. Karpenko

Cold War Soviet Prototypes 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.


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


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.


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


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


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.


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
Cold War Soviet Prototypes

1K17 Szhatie

Soviet Union (1990-92)
Self-Propelled Laser Complex – 1 prototype

The mysterious 1K17 Szhatie (also known as 1К17 Сжатие – ‘Compression’ in Russia, and as the ‘Stiletto’ in NATO reporting) was a unique project developed by the Soviets just before the collapse of the Soviet Union in 1991. This laser-armed tank was designed to be a type of anti-missile system. It could also disable enemy optoelectronic systems, including imaging equipment such as sights, scopes and cameras.

The 1K17 Szhatie. Photo: Vitaly V. Kuzmin


A laser-armed tank may seem like something out of Buck Rogers or Star Wars (the latter being popular at the time of the vehicle’s original conception), but this was a very real project. The idea for such a vehicle appeared in the late 1970s, early 1980s, in the form of the SLK 1K11 Stilet. This was a relatively simple vehicle, being little more than an APC with a small laser lamp on its roof.
A further development was the Sanguine, based on the ZSU-23-4 Shilka SPAAG (Self-Propelled Anti-Aircraft Gun) with a large single laser emitter mounted in place of the guns. Little is known about the trials and success or failure of these projects. There is information to suggest that during testing that the Sanguine’s laser once knocked out a helicopter’s optical system at a range of 6 miles (9.65 km) and disabled the aircraft entirely at 5 miles (8.04 km).
The project would be revisited in the late 80s, with a more elaborate design. This Self-Propelled Laser Complex (S.P.L.C.) was designed by Nikolai Dmitrievich Ustinov. Ustinov was a scientist, radiophysicist and radio technician, but specialized in laser technologies. He was even the head of a school dedicated to laser technology. The vehicle was constructed at Uraltransmash (The Ural Transport Machine-Building Plant) in Yekaterinburg, under the supervision of Head Designer, Yuri Vasilyevich Tomashov.
The first prototype of the vehicle was assembled in December 1990. In 1991, 1Q17, as it was then designated, took part in field trials which lasted until 1992. The trials were considered a success, and the S.P.L.C. was approved for construction and service, though Mr. Ustinov, unfortunately, would not live to see it, as he passed away in 1992. For a variety of reasons, it would never see service or full-scale production.

A Design From the Future

The 1K17 was based on the chassis of the 2S19 ‘Msta-S’ Self-Propelled Howitzer. The gun was removed from the 2S19’s turret and it was heavily modified. The ’Solid-State’ Laser equipment was introduced into the subsequent void left by the gun. Solid-State is a type of laser that uses a solid focusing medium, as opposed to the liquid or gas of most common high-power beam emitters.
The project soon became an extremely expensive endeavor, as the solid medium of choice for this extremely powerful laser was artificially grown rubies, each one weighing 30 kg. (66.1 lb). There were 13 laser tubes in the emitter, each one filled by a ruby. The ruby crystal was formed in the shape of a cylinder. After it was harvested, the ends were polished and covered with silver which acted as focusing mirrors. In operation, Xenon gas would spiral around the ruby. The luminescent gas was ignited by lamps in the crystal housing, which would, in turn, ignite the laser beam. The range of the beam is not known, but it is probably similar to that of the Sanguine’s; 5 – 6 miles (8.04 – 9.65 km).
It is also estimated that the laser had a pulse mode that was achieved with an aluminum-garnet device that had neodymium additives. This gave off large amounts of power in short bursts and would give the laser a pulsing effect.

A Dangerous Weapon?

As a defensive weapon, the laser was extremely effective in disabling enemy vehicles, weapons and visual equipment. It could also be used an offensive weapon, against biological targets such as humans, either pilots, crew, or infantry etc. Much of the information available regarding the effect of lasers on humans come from small-scale tests. The source for the subsequent info comes from a recording of such tests, in the book Effects of High-Power Laser Radiation by John F. Ready.
As described previously the system could disable enemy equipment. The prototype built on the Shilka is recorded as having downed a helicopter during testing. A laser this size and radiation output could easily cause computer systems to shut down. Plastics and thin metals would likely melt or warp, ruining structural integrity.
With regards to biological effects, it is well known that even pocket lasers and small-scale lasers can cause damage to the human eye with heavy retinal burns and scarring. This can result in complete blindness. This effect would be amplified due to the size and power of the 1K17’s laser system, probably resulting in instant blinding. It isn’t known to be the case, but it is likely that that the entire crew of the vehicle wore eye protection in the form of tinted goggles matched to the frequency of the light emitted. These are used in most cases when handing lasers outside of military use. The crew of any enemy vehicle looking through a telescope or gun sight would likely be blinded.
Here marks a controversial point where this weapon, if it had entered service and was used in such a fashion, would breach Geneva Convention protocols. Below is article one to three from the Convention’s Blinding Laser Weaponry protocol which was put forward by the United Nations on October 13, 1995. It came into force July 30th, 1998:
Article 1: It is prohibited to employ laser weapons specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision, that is to the naked eye or to the eye with corrective eyesight devices. The High Contracting Parties shall not transfer such weapons to any State or non-State entity.
Article 2: In the employment of laser systems, the High Contracting Parties shall take all feasible precautions to avoid the incidence of permanent blindness to unenhanced vision. Such precautions shall include training of their armed forces and other practical measures.
Article 3: Blinding as an incidental or collateral effect of the legitimate military employment of laser systems, including laser systems used against optical equipment, is not covered by the prohibition of this Protocol.

A close-up view of the emitter set up. Photo: Vitaly V. KuzminReactions of skin and other bodily tissue is a different matter. The effect of laser radiation varies between the skin tones and keratin levels, but overall results are similar. With a high-power laser emitting at lower levels, lesions and dead skin begin to appear. With increased power, the damage worsens. Severe burns can occur with damage to blood vessels, leading to heavy charring and necrosis. Internal organs can also be badly damaged, especially the brain if the head is fully exposed. Death can occur with exposure to the brain by causing deep lesions and extreme hemorrhaging. One should remember, that effects described here would be amplified greatly due to the size and power of the 1K17’s emitter. It may not have been designed to be offensive, but it could certainly be a dangerous weapon if deployed in such a manner.


The turret of the 1K17 was extremely large, being almost as long as the hull, housed the huge laser emitter. There were 13 lenses in the emitter, these were mounted in two rows of six, with one lens in the center. When not in use, the lenses were covered by armored panels. It is unknown to what degree – if any – the emitter can elevate or depress, though there is what appears to be pivot points either side of the emitter housing. Also, given that one of the laser’s intentions was to disable incoming missiles, it is likely that it can elevate to aim at airborne targets.

This view of the emitter shows the armored panels that cover the lenses when not in use. Photo: Vitaly V. Kuzmin
The rear of the turret was taken up by a large autonomous auxiliary generator unit that would provide power to the emitter. Towards the rear of the turret on the right was a cupola for the commander, mounted on here was a 12.7mm NSVT Heavy Machine Gun for self-defense. Aside from this, the tank had no other regular, that is to say ballistic, weaponry to fall back on in a defensive situation apart from any personal weapons the crew might carry. It also had six smoke dischargers. These were mounted in two banks of three on either side of the emitter on the turret cheeks.


As mentioned, this vehicle was based on the design of the 2S19 SPG, which in turn was based on the hull of the T-80 Main Battle Tank. The chassis of which was mostly unaltered apart from being lengthened slightly for improved stability. It was powered by the T-72’s V-84A Diesel engine, rated at 840 hp. This gave the SPG a speed of 37 mph (60 km/h). The driver’s position was in the center, at the front of the vehicle.

A full view of the 1K17’s hull and turret. Photo: Vitaly V. Kuzmin


The turbulent economic wake of the USSR’s disintegration in 1989, with revisions to the state’s financing of defense programs, was the death warrant for the 1K17 project. Only one vehicle was built. Its existence was only recently revealed, and the exact properties of the laser system remain classified, with no open source of data. The number of crew that operated the vehicle is even unknown.
The 1K17 does survive, however. It is preserved and displayed at the Military Technical Museum at Ivanovskaya, near Moscow. It is unclear what happened to the Stilet and Sanguine. The Stilet was photographed in 2004, at a military scrap yard near St. Petersburg. It has not been seen since.
At this time the status of Russian laser weapons development is not known but there is no information to suggest that such weapons are not currently in development although none are known to have ever been operationally deployed. The Szhatie was not the last Russian ‘laser tank’, however. Though it does not operate in the same manner, the KDHR-1H Dal (meaning ‘Distance’) is a chemical detection and monitoring vehicle and is equipped with a laser radar that can scan 45 square miles in 60 seconds. This vehicle is currently in service with the Russian Military.

An article by Mark Nash

1K17 Szhatie specifications

Dimensions (L-W-H) 19.8 x 11.7 x 11 ft (6.03 x 3.56 x 3.3 m)
Total weight, battle ready 41 tons
Crew Unknown other than Commander and Driver
Propulsion V-84A Diesel engine, 840 hp
Speed (on/off road) 37.2 mph (60 km/h)
Armament 1 high-power laser complex, 15 seperate lenses,
1 x 12.7mm NSVT Heavy Machine Gun
Total production 1
For information about abbreviations check the Lexical Index


John F. Ready, Effects of High-Power Laser Radiation, Academic Press
An article on the 1K17
An article on (Russian)
The 1K17 on
An article on Self-Propelled Lasers
A full collection of 1K17 images on Vitaly V. Kuzmin’s website,

Illustration of the 1K17 Szhatie by Tanks Encyclopedia’s own David Bocquelet. (Click to enlarge)

Cold War Soviet Prototypes

IS-7 (Object 260)

Soviet Union (1946-48)
Heavy Tank – 7 prototypes

The IS-7 (ИC-7), starting life under the project title of Object 260 (объект 260), followed on from the ill-fated IS-5 (Object 730) and IS-6 (Object 252/253). With these failures, the request was still standing for the USSR’s next heavy tank.
The IS-7 was the brain-child of the Soviet tank designer Nikolai Fedorovich Shashmurin. As well as having a hand in the design of the rather successful IS-2 which would serve well in the later years of World War II, Shashmurin also drew up plans for the ill-fated KV-4 (Object 906) project, which never came to fruition.
The IS-7 would be Shashmurin’s crowning glory and could be considered the zenith of the Iosif Stalin heavy tanks. At the time of its conception, it was one of the most technologically advanced heavy tanks in the world, and one of the most heavily armored.


The seeds of the IS-7 were first sown in December 1945 in Factory No. 100 in Leningrad, with a full-scale wooden mock-up produced soon after. Running prototypes were ready for testing in 1946. These tests ran through 1947, ending in 1948 when the designers believed they had reached a finalized design. It was then given the title of IS-7. This final design was armed with a stabilized 130 mm (5.12 in) cannon fed by an autoloader, a total of 8 machine guns, infrared scopes, and armor up to 300 mm (11.8 in) thick. It was the largest tank that the USSR had or would ever produce.
The wooden mockup of the IS-7, at this point known as the Object 260
The wooden mockup of the IS-7, at this point known as the Object 260


The tank was designed to withstand the impact of a shell fired by the 12.8 cm Pak 44 Gun found on the German Jagdtiger. The armor on the IS-7 was up to 300 mm (11.8 in) thick, some of the thickest being found on the specific pike nose, formed from homogenous steel. The upper plates were 150 mm (5.9 in) thick angled at 60 degrees. The lower glacis 100-120 mm (3.94-4.72 in) with a slight angle.
Rear cutaway view of the IS-7. Note the thicknesses of the armor on the turret and hull sides.
Rear cutaway view of the IS-7. Note the thicknesses of the armor on the turret and hull sides.
The side armor was also not to be underestimated. The upper hull was 150 mm (5.9 in) thick, while the lower sides measured 100 mm (3.94 in) and was curved outwards, meeting the upper hull seamlessly. The bending of the lower hull was done in a large press, which literally forced the metal into shape.
The mantlet was 350 mm (13.8 in) thick. The turret itself was cast, with the cheeks being the thickest part at 240-250 mm (9.45-9.84 in). They were angled, or curved, at about 50-60 degrees. The shape of the turret was extremely rounded and smooth all the way around, with no obvious shot traps or prominent cupola. There were slightly raised portions of the turret roof where crew positions were found. The commander’s station on the right was slightly higher than the gunner’s one found on the left. The top of these raised portions had direct vision blocks.
In a hull-down position, the turret would have been almost impenetrable. The armor proved not only immune to the intended 12.8 cm, but also the tank’s own 130 mm cannon.


The IS-7’s main armament consisted of the 130mm (5.11 in) S-70, although it was originally intended to carry the S-26. The S-70 was derived from a naval gun. It had a barrel length of 54 calibers. The gun could fire a 33.4 kg shell at 900 m/s and was able to penetrate up to 163 mm (6.4 in) of armor, sloped at 30 degrees, at ranges up to 2000 meters.
The 130 mm S-70 gun with the coaxial KVPT on top.
The 130 mm S-70 gun with the coaxial KVPT on top.
As mentioned above, the IS-7 was equipped with an autoloader. It is not an autoloader in the current sense of the word, however. A more accurate description would be an Automatic Loading Assistance Device, that would be operated by the tank’s two loaders. This piece of equipment was located in the turret bustle. The ammunition of the IS-7 was composed of two parts, separately loaded. As such, the charge was at the bottom of the device, while the projectile sat above. It was operated by a crank handle. The first turn would drop a projectile onto the conveyor belt located in the center of the system, a few more turns would drop the propellant behind. The conveyor would then carry the ammunition to the mouth of the breach, where it would be rammed in. The conveyor would then lift clear of the gun. The gun then fired and the process began again.
The IS-7s loading system
The IS-7s loading system.
This theoretically gave the tank a 6 to 8 rounds per minute rate of fire. Whether actual operation matched this time is unknown, as it doesn’t take into account the reloading of the device. However, it could technically be resupplied as it worked from the various ammunition racks inside the vehicle. The tank carried 25-30 rounds. The downside of this system was that the gun had to return to a neutral position for the loading device to work, meaning the gunner would have to re-lay the gun onto to a target after each shot. Should the mechanism go down, the gun could be manually loaded of course.
To say that the IS-7 was lacking in secondary armament would be an understatement of the highest order. The IS-7 was equipped with no less than 8 machineguns. Four of these were 7.62 mm (0.3 in) SGS-43s and they were mounted in a unique way. Two were placed on both flanks of the hull, towards the rear, fixed in place and fired by the driver. The machine guns were housed in a simple armored box. There were separate shoots for the spent casings and belt links. The ammunition was stored underneath.
There were two more of the machine guns fixed on the rear of the turret, facing backward. These two were staggered to accommodate the large ammunition shoots on the turret roof. Sheet metal boxes were attached to the outside of these to collect the belt links, but casings were left to fall away. It is believed these guns were operated by the gunner or loader who would take aiming orders from the commander to turn the turret left or right. The practical use of these weapons is highly questionable. Whether they would have stayed on a production model is unknown, but some of the prototypes were not equipped with the ones on the turret.
The roof was home to a 14.5 mm (0.57 in) KPVT heavy machine gun on an AA mounting that could pivot down to the left when not in use. The only way to operate this gun was by standing on the engine deck. There were tests to see if it could be remotely controlled by the commander, but these were unsuccessful.
The IS-7 had no less than 3 coaxial machine guns. As well as the KPVT mounted on top of the main armament, 2 SGS-43s were mounted either side of it.


The IS-7 was powered by the M-50T 12 cylinder diesel engine, rated at 1050 hp, and was derived from a naval marine engine. It would run through an 8-speed planetary gearbox. This would propel the vehicle to 60 km/h (33 mph) on roads, a respectable speed for a tank weighing 68 tons fully loaded. Spare diesel fuel could be stored in canvas pouches in compartments towards the rear of the vehicle on each flank.
The weight of the IS-7 was supported on 7 roadwheels on each side. These wheels also supported the return of the track, as there were no return rollers. Each wheel was attached to a road wheel arm, in turn, attached to the torsion bar suspension. The wheels had internal rubber bushings to give the all-metal wheels an extended service life.
The tracks of the IS-7 were some of the first in Soviet use to have a retaining clip in the track link pins, instead of having to rely on a wedge of metal welded to the lower hull to whack the pins back in.

Photo: – Alexey Khlopotov


After the initial factory tests, the prototype tanks were handed over to the State Commission. The test drivers were famously fond of how the IS-7 handled. Reporting that it would respond to the smallest adjustment with ease. The tests were not without incident, though.
During one of the trials, an IS-7 caught fire, despite both sets of internal extinguishers firing, the fire continued to burn resulting in the abandonment of the vehicle and its complete destruction. The cause of the fire was thought to have originated with the weight-saving plastic lined canvas fuel tanks. Quite understandably, these were deleted in later versions.
Though it was liked and generally thought to be a good vehicle, the governing bodies refused to accept it into mass production. The official reasons are not known as to it was rejected. As such, the IS-7 would never enter service, with its successor, the IS-8, later known as T-10, proving to be a more flexible vehicle and able to better meet the needs found on the now fast moving battlefields. It served from 1953 to 1996.
Only one IS-7, built in 1948, survives today and is currently on display at the Kubinka Tank Museum.
The IS-7 as it stands today in the Kubinka Tank Museum
The IS-7 as it stands today in the Kubinka Tank Museum, alongside the IS-4.

Planned Variants

Object 261

While work was ongoing with the IS-7, plans were drawn up for a self-propelled gun variant based on the IS-7’s hull. There were 3 planned versions, the Object 261-1, -2 and -3. The 261-1 was a closed type with the fighting compartment on the bow end of the vehicle. It was armed with a 152 mm (6 in) M-31 gun. The configuration was similar to the ISU series.
The 261-2 had a rear mounted open fighting compartment. For this version and the following, the chassis was reversed, meaning the drive wheels were now at the front of the vehicle. What was the IS-7’s front was the 261-2’s rear. It was armed with a long-barreled M-48 152 mm (6 in) gun. The Object 261-2 was later redesignated Object 262.
The 261-3 had the same configuration as the 261-2/262, but was up-gunned with the naval derived 180 mm (7.09 in) MU-1 gun, also known as the B-1-P. Despite them being Self Propelled Guns, designed to be behind the lines giving fire support, these vehicles were intended to be well armored, with armor 150 to 215 mm (5.91-8.46 in) thick. The vehicles didn’t go further than the scale model phase.
The small-scale mock-up of the Object 261-2/261-3
The small-scale mock-up of the Object 261-2/261-3. A Recoil-spade was also added to the rear.

Object 263

This was a tank destroyer variant, built on the same configuration to the 261. It had a rear mounted, semi-open fighting compartment. The main armament was the 130 mm (5.12 in) S-70A, with separately loading ammunition. This was a slightly modified version of the IS-7’s gun. The armor was up to 250 mm (9.84 in) thick, with a large, flat slab on the front of the vehicle, and two plates either side of the gun mantlet. The side armor was up to 70 mm (2.76 in).
As with the 261-2 and -3, the IS-7 chassis was reversed, a configuration similar to the British Archer. The driver was moved to the left of the gun. Whether the 263 would have had the same issue of the Archer’s engine heating the middle of the barrel and throwing off accuracy is unknown. Like the 261, the vehicle never went further than small scale models.
The small-scale mock-up of the Object 263
The small-scale mock-up of the Object 263. The 263 also saw the addition of a recoil-spade on the rear.

An article by Mark Nash

IS-7 (Object 260) specifications

Dimensions (L-W-H) 7.3 m x 3.3 m x 2.4 m (24ft 2in x 11ft 1in x 8ft 1in)
weight 68 tonnes
Crew 5 (driver, gunner, 2x loaders, commander)
Propulsion 1050 hp 12 cylinder M-50T diesel engine
Suspension Independant torsion bar
Speed (road) 60 km/h (33 mph)
Armament 130 mm (5.11 in) S-70
2x KPVT 14.5 (0.57) MGs
6x SGS 7.62 (0.3 in) MGs
Armor Hull: 150 mm (5.9 in, upper glacis, angled at 60 degrees) – 100-120mm (3.94-4.72 in, lower glacis). Side armor is 150 mm (5.9 in) – 100 mm (3.94 in).
Turret: 240-250 mm (9.45-9.84 in)
Total production 7 prototypes

Links & Resources

An article on the IS-7 on FTR
An article featuring the IS-7
The above link uses the following literature as the primary source: Heavy Soviet Post-War Tanks. Written by M. Baryatinsky, M. Kolomiets and A. Koschavtsev. “Armour Collection #3, 1996”
The IS-7 on (Czech)
The IS-7 on (Russian)
English translation of the article

Illustration of the IS-7 by Jarosław Janas
Illustration of the IS-7 by Jarosław Janas.

Illustration of the IS-7 by Tanks Encyclopedia’s own David Bocquelet.

Cold War Soviet Prototypes

Object 416 (SU-100M)

USSR (1950)
Light tank/SPG – 1 prototype built


Object 416 was born in the famous city of Kharkov. It was designed by The Construction Bureau of Plant No. 75. In 1944, the same design bureau had designed the A-44, a rear-turreted medium tank. The A-44 never saw development as a consequence of the ensuing Russo-German hostilities.
In 1950, the team started with a fresh blueprint, taking inspiration from their older design. The design was for a light tank with a low silhouette that would be well armored, but not overly heavy.


In 1951 the requirements for the project were altered. Due to its general characteristics, the vehicle was redesigned as a self-propelled/assault gun. Technical problems with the turret meant a working prototype was not ready until 1952. By 1953, the design had developed a little bit more, and had a properly functioning turret.
The Object 416 prototype in Kubinka. The low height of the vehicle can be observed. - Source:
The Object 416 prototype in Kubinka. The low height of the vehicle can be observed. – Source:
What came out of this was the Object 416, a lightweight vehicle with an extremely low profile and a rear mounted turret. The vehicle weighed just 24 tons, and was only 182.3 cm (5’2”) high. It was moderately armored with hull armor of only 75 mm (2.95 in) and frontal turret and mantlet armor of 110 mm (4.3 in).
The turret, though designed solely for this vehicle, shared a lot of features with the T-54’s, but was greatly expanded. It was abnormally large for a vehicle of its class and size, but for good reason. All 4 of the crew, including the driver, were positioned in the rear mounted turret. The driver sat at the front right. An ingenious system was developed, meant to allow the driver to remain facing towards the front of the vehicle regardless of where the turret was pointed. On paper, the turret was capable of a full 360 degrees of traverse, however, the driver’s seat would only rotate so far. This meant that the arc was reduced to 70 degrees left and right while the vehicle was on the move. The was also responsible for loading the 7.62 coaxial machine gun to his left.
The main armament of the 416 was the 100 mm (3.94 in) M63 cannon, a derivative of the D-10T gun found on the famous T-55. Its ballistic characteristics would have probably been much the same. For reference, the T-55’s Armor-Piercing rounds could penetrate 97 mm (3.82 in) at 3000 m (3300 yds), with its Armor-Piercing Ballistic-Cap penetrating 108 mm (4.25 in) at the same distance. These values relate to D-10T, as ballistic reports on the M63 are sparse to say the least. To reduce the effect of the heavy recoil on what was essentially a light tank, the gun was tipped with an elaborate Quad-Baffle muzzle brake. The gun was also equipped with a bore evacuator to assist in venting fumes from the cannon after firing.
Illustration made by the user Tin53 on the WoT EU forum
The gun could elevate to 36 degrees, in theory meaning it could take extremely effective hull down positions (as seen to the left). But the rear mounted turret meant the gun only depressed to -5 degrees.
An innovative feature of the gun was its chain drive loading system. The loader would drop the shell onto the tray, and the chain system would then ram the shell into the breach, saving him the arduous task of loading what is quite a large shell in a cramped fighting compartment. Of course, in the event of the chain-drive failing, the shells could be loaded manually. After loading, the chain drive would be folded out of the way to avoid being struck by the recoiling gun breech. The tank carried 18 ready rounds of 100 mm ammunition (AP: Armor-Piercing, APBC: Armor-Piercing Ballistic-Cap, APHE: Armor-Piercing High-Explosive) in the rear of the turret. There was more ammunition storage in the rear of the hull.
Under the almost bare forward hull, laid the tank’s power-plant, a 400 hp, V12 Engine. This allowed the tank to reach a top speed of 45-50 km/h. The tank’s torsion bar suspension system and track were designed specifically for it. Unusually for Soviet tanks of the time, the sprocket wheels were at the front of the vehicle. The tracks use external guide horns, rather than the more traditional center guides used on most Soviet tanks of the era.

Top-rear view of the Object 416. The size of the turret compared to the rest of the hull can be observed - Source:
Top-rear view of the Object 416. The size of the turret compared to the rest of the hull can be observed – Source:
The Object 416 during Testing
The Object 416 at Patriot Park in April 2016 - Credits: Vitaly Kuzmin
The Object 416 at Patriot Park in April 2016 – Credits: Vitaly Kuzmin


As development continued, problems arose that would affect its intended role as a light tank. Problems with steering, and firing on the move hindered the development. As such, the vehicle became more of a Tank Destroyer, and as such was re-designated as the SU-100M. One source suggests that this was the only way the project would continue to be funded.
The vehicle itself never saw service or production, losing out in tests to the SU-100P. Ironically this vehicle also ended up as a canceled project. The two vehicles sat for a long while side by side at the Kubinka Tank Museum. The Object 416 is now at the Patriot Park in Kubinka.

An article by Mark Nash

Object 416 specifications

Dimensions 6.35 oa x 3.24 x 1.83 m (20’9” x 10’8” x 6′)
Total weight, battle ready 24 tons
Crew 4 (driver, gunner, loader, commander)
Propulsion 12 cylinder Boxer diesel, 400 hp
Suspension Unsupported torsion bar
Speed (road) 45 km/h (28 mph)
Armament 100 mm (3.94 in) L/58 M-63
7.62 mm (0.3 in) coaxial machine-gun
Armor Hull: 60/45/45 mm (2.36/1.77/1.77 in)
Turret: front 110 mm, +110 mm mantlet (4.33, +4.33 in)
Total production 1 prototype

Links & Resources

Object 416 on FTR
The Object 416 on Dogs of War (Russian)
The Object 416 described by Mihalchuk-1974 (Russian)

Tank Encyclopedia’s own illustration of the Obj. 416 by David Bocquelet.