Cold War Soviet Heavy Tank Prototypes

Object 718

Soviet Union (1945-1948)
Superheavy Tank – Blueprints Only

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

The fascination for super-heavy tanks was a common theme prior to the Second World War in several nations and continued into the war. The Soviets had their own fair share of such heresies, such as the Edward Grote’s designs, T-42, KV-4, and KV-5 and more. However, the theme of such heavy tanks slowly died during the war, with the occasional exception. One such exception was the Object 718, often called Object-705A – a 100-tonne super-heavy tank armed with a 152 mm gun and having dozens of centimeters of raw armor, as Soviet tank design moved towards more advanced protection philosophies, such as low silhouettes and steeply angled plates requiring thinner armor.

Yet, with the discovery of the German monster tanks, like the Maus and Jagdtiger, Soviet officials realized that their own heavy tanks were inferior. Although the war was over, further developments on even heavier tanks continued. On the 11th of June, 1945, the GABTU ordered the development of a 60-tonne heavy tank armed with a S-26 130 mm gun and the suspension had to be torsion bars. Kirov Chelyabinsk (ChKZ) answer to this request came in the form of the Object 705 and Object 718, while Kirov Leningrad (LKZ) came in the form of the Object 258, Object 259 and Object 260 (IS-7).

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

One of the final IS-7 prototypes. While certainly a massive tank, and likely on par with the Object 705A in terms of dimensions, the 100-tonne weight of the Object 718 makes them hard to compare.


The Object 718 was a direct evolution from the Object 705, a lighter 65-tonne heavy tank. Both vehicles featured a rear-mounted turret for better balancing of weight and to reduce gun overhang. The Object 705A was to be armed with a colossal 152 mm M-51 gun, using two-part ammunition and two loaders. Weighing 100 tonnes on paper (a figure likely to grow as the design would transition from paper to reality), the armor would have been impressive in raw thickness, yet clever use of angling the side armor plates into a diamond-like shape, the overside protection was increased. To protect itself from infantry, soft-skin vehicles, and even aircraft, a secondary turret was added to the rear of the turret, armed with 2 KPVT 14.5 mm heavy machine guns.

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

Silhouette of the Object 705. The Object 718 would have likely been similar in layout, just larger.
Source: TiV No. 09 2013


The exact details of the tank remain mostly unknown. Even a full blueprint of the hull is, so far, missing. Careful analysis and speculation would indicate that the hull was very similar to that of the ‘lighter’ Object 705, but lengthened to fit the larger turret and heftier rounds. The Object 718 would have been 35 tonnes heavier, out of which at least 10 tonnes would come from the larger turret and the 152 mm gun and its ammunition. The remaining 25 tonnes would likely come from thicker frontal armor, overall increased hull volume, and a new engine. This new engine would have been either a diesel or turbinepower output of 2,000 hp, to be able to reach useful speeds. This engine was likely the outcome of post-war Soviet-German work on turbine engines. The transmission was a planetary system automatic. In terms of suspension, a single torsion bar per wheel was used.

One of the main reasons behind the Object 718 was for more armor. Although the exact armor values are yet unknown, comparison to the Object 705 and other heavy tanks of the time (also taking in consideration the weight) results in the frontal hull being at least 220 mm thick, angled at circa 60 degrees. The side armor would be at least 150 mm thick angled inwards at circa 57°. The rear armor angled upwards and was at least 120 mm thick. According to a document on the project, it was to whitstand incoming shells with a muzzle velocity of 1200 m/s.

152 mm M-51

One of the few certain things about the Object 718 is the main armament, the M-51 152 mm gun, developed at Factory No.172 as a tank variant for the 152 mm M-31. In terms of ballistics, it was mostly identical to the regular M1935 Br-2 howitzer, but with considerable upgrades in other areas. Firstly, the archaic breech block door was replaced with a more modern horizontal sliding breech block. It also received the famous TsAKB style slotted muzzle brake, which could absorb up to 70% of the recoil, decreasing the need for powerful recoil absorption pistons. It still had two recoil absorption cylinders and two brake cylinders to absorb recoil, but these were considerably lighter, and in tandem with the muzzle brake, decreased the recoil from 1,400 mm (on Br-2) to 520 mm. Very noticeable is the sheer volume of the breech, which was needed to offset the long barrel. One prototype of the gun was built and passed factory tests in the summer of 1948.

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


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

On the roof of the turret, the turret ring of a second, smaller turret can be seen. This was a brand new design feature incorporated on some heavy ChKZ designs, first incorporated on the Object 726, and apparently, also the Object 718 (as the two were likely designed simultaneously). The turret resembles contemporary American tank secondary turrets, having a hemispherical shape. It was armed with a pair of 14.7 mm KPVT heavy machine guns. It was far too small for a crew member to fit in it, and was probably mechanically controlled from within the turret by one of the loaders. The idea was not entirely dropped after the cancellation of these super-heavy tanks. The Object 777 still used a similar turret, but with only one turret KPVT. For the turret traverse, ChKZ created hydraulic drives in 1948, but they were deemed unsuccessful and shortly after, the entire project was canceled.

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

Suspension & Running Gear

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

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

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

Side cutout view of the wheels used on the Object 718. These were likely designed specifically for the project.
Source: TiV No. 09 2013
Side cutout view of the torsion arm and torsion bar attachment on the Object 705A. Note the steep angle of the hull.
Source: TiV No. 09 2013
Cutout top view (left) and cutout side view (right) of the torsion bar arrangement. Note how they are mounted in opposite facing pairs, an unusual solution.
Source: TiV No. 09 2013

A Maturing Tank Force

Although being under development for almost 3 years (a very long time for Soviet standards), the Object 718 never got particularly far. Both the GABTU and Soviet officials began discouraging especially heavy tank projects. Even internally, ChKZ was focusing on other, more fruitful projects, like the IS-3 and IS-4 or various self-propelled guns.

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

In contrast, heavy tanks, especially super heavy ones, like the Object 718, would hinder the Soviet tank force rather than improving it. Such a heavy tank, not only requiring massive amounts of money and resources poured into developing, production and maintenance, would also require an entirely new logistical force, from rail cars to mobile bridges.

Ultimately, the Object 718, alongside its lighter brother the Object 718 and its LKZ rival, the IS-7, all got their lives cut short by the Council of Ministers of the USSR on the 18th of February, 1949, where it was requested that the development of all heavy tanks and SPGs weighing over 50 tonnes should be terminated.

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

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

The Object 718 (incorrectly known as Object 705A). Illustrated by Pavel Alexe

Object 718 Specifications

Dimensions (L-W-H) 7.2 – 3.7 – 2.4 m
Total Weight, Battle Ready 100 tonnes
Crew 5 (Commander, Gunner, Driver & 2 Loaders)
Propulsion 2000 hp diesel/turbine engine
Speed 35 km/h (hypothetical)
Range Torsion bar, 7 wheels per side
Armament 152 mm M-51 gun
coaxial 14.5 mm KPVT heavy machine gun
Secondary turret w/ dual 14.5 KPVT
Armor Hull armor:
Front top plate: 220 mm at 55°
Front bottom plate: 200 mm at -50°
Side plates: 150 mm at 57° (inwards)
Rear plates: 120 mm
Top: 30 mm
Belly: 30 mm
Total Production 0, blueprints only


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

Cold War Soviet Heavy Tank Prototypes

Object 705 (Tank-705)

Soviet Union (1945-1948)
Heavy Tank – None Built


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

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

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

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

Development first began in June 1945, immediately after the discovery and analysis of German heavy AFVs. This triggered a series of projects over several design bureaus and factories. For ChKZ, the IS-3 was proving to be a success, and the IS-4 (Object 701) was soon to enter production. In contrast, LKZ had just lost several programs, most importantly, the IS-6. But the experience gained from it led to a series of promising designs. Fast forward a couple of years, and LKZ had full-scale mock-ups of one of the best heavy tanks ever designed, and was beginning prototype production. Meanwhile, Chelyabinsk and its design institute, SKB-2, had a series of disappointments, especially in the IS-4. In parallel, ChKZ had been working on the Object 705 and 718 (also called Object 705A) designs, but, as they were not deemed crucial or urgent, progress was slow. Further problems came with the 80th order on 2nd April, 1946 from V.A. Malyshev, when the mass of heavy tanks was limited to 65 tonnes. While the Object 705 still fit the criteria, the Object 718 did not. Yet work continued regardless.

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


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

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

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


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

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

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

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

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


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

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

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

Roadwheels and Suspension

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

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

Yet blueprints of the Object 718 show a slightly different set of wheels. These were drawn as steel rimmed and with deep spacing between the rims and rest of the stapled steel lids. The wheels seem to have been mostly unique to the Object 705A. The Object 705 could have used the same wheel design or something else, as the lower weight allowed for more playroom in terms of weight thresholds on the components.

Cutout view of the roadwheel used on the Object 718. These were different to other large-diameter wheels used by ChKZ.
Source: TiV No.9 2013

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

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

Object 705A

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

Conclusion – Weight Shaming

With so little information available, it is hard to properly judge the capabilities of the Object 705 and 718, even when compared to the different variations of the IS-7. The vehicles were likely designed between 1947 and 1948, at which point the BL-13 was already outclassed (Kirov Leningrad had used it on the IS-6 and other projects in 1945). So, in that respect, the Object 705 fell behind the IS-7. Yet in terms of armor, it was on par, if not even better protected than the most advanced IS-7 variant. As for the Object 718, the lack of information prevents any conclusions to be drawn, with the one and main issue being the weight of 100 tonnes. When discussing both the Object 260s and Object 705s, it is generally clear that such heavy vehicles could prove vulnerable and simply too heavy for effective battlefield use. The heaviest Soviet tank in service, the IS-4, weighed 53 tonnes and was still considered overweight and too slow. Thus it seems almost natural that the Soviet government saw the limitations and waste of resources devoted to such heavy vehicles. The final nail in the coffin for these designs was the cancellation of all AFVs above 50 tonnes on 18th February, 1949.

Object 705 rendition, illustrated by Pavel ‘Carpaticus’ Alexe

Object 705 specifications

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


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

Cold War Soviet Heavy Tank Prototypes

K-91 (Rear-Mounted Turret)

Soviet Union (1949)
Heavy Tank – 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 Heavy Tank Prototypes Has Own Video

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 Heavy Tank Prototypes Has Own Video WW2 Soviet Heavy Tank Prototypes

Object 257

Soviet Union (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 mm
Turret armor
Front: 150 mm
Side: 150 – 120 mm
Rear: 100 mm
Top: 30 mm
Total Production 0; blueprint only
Cold War Soviet Heavy Tank Prototypes

IS-7 (Object 260)

Soviet Union (1946-1948)
Heavy Tank – 7 Prototypes Built

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 224) 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.