IS-7: A titan too late for the war

Article from translated by comrade Robopon for TAP. It’s his first translation, so please provide feedback.

IS-7 (ИС-7) was born in a strange and difficult time for the soviet tank industry. The Red Flag over the Reichstag brought not only the joy of victory but also problems for all aspects of Soviet post-war industry. Destroyed cities needed to be rebuilt, evacuated factories needed to be brought back, everything needed to be changed.

The Commissariat of Tank Industry was reformed into the Commissariat of Transport Engineering and in early 1946 it was renamed into a Ministry of the same name. Wartime fighting vehicles needed to be upgraded according to a new doctrine for the time of peace. They needed to be more reliable in order to provide longer service, since immediate war losses weren’t a factor anymore. A lot of works on future projects were terminated and others were developed with lesser enthusiasm.

Among those post-war projects was a tank later named “Object 260” («Объект 260»). The works on this one started way back in 1944. It was planned that this vehicle would embody all advancements of Soviet heavy tank design at that time. The project was assigned to the design bureau of Josef Kotin at Experimental Factory № 100.

Other variants of this project were created in the spring of 1945: “Object 257”, “Object 258” and “Object 259”. After all considerations, the final variant of the vehicle was presented and designated “Object 260”, more known as IS-7.

Over 20 institutions and science facilities were assigned for its development. They proposed a lot of unique technical solutions never used before in such machines.

The working blueprints of IS-7 were finished already in September 1945. The frontal armor was made similar to the IS-3, but much thicker, 150 mm of upper front plate (pike nose) instead of 100 mm of its predecessor. The mass of the vehicle was quite impressive at 65 tons.

Such a heavy vehicle needed a new, more powerful engine, capable of around 900-1200 hp. The development of such an engine was assigned to multiple facilities, but none of them was having much of a success until the Kirov factory in cooperation with factory № 500 presented a new engine named TD-30 that allowed the speed of up to 60 km/h on hard terrain and around 30 km/h on soft terrain. The engine was installed on the first two IS-7 prototypes. The quality was deemed unsatisfactory, a lot of work was still required so the TD-30 engine was later changed to the 1050 hp M-50T naval diesel engine.

The torsion bar suspension for the new tank was developed from suspension variants tested on serial vehicles and included a lot of new and unique ideas for Soviet engineering, like dual action shock absorbers and various hydraulic assists which in result reportedly made the tank very easy to control.

A new 122mm cannon was put into development and planned to be mounted on “Object 260”, but the work wasn’t completed in time. In early 1946 the Central Design Bureau of Ordnance was assigned to develop a new 130mm cannon named S-26, whose ballistics were close to the B-13 naval cannon of the same caliber. An autoloading mechanism with a conveyor belt feeding system was used to achieve a rate of fire of around 6 shots per minute. In addition to the main armament, multiple machineguns were installed: one 14,5mm coaxial and six 7,62mm.

The first IS-7 was completed on September 8th 1946. Until the end of this year the tank reached a mileage of 1000km and the trials were deemed successful. The second vehicle was issued on December 25th and never completed any real driving tests. In addition to two preproduction models several more parts were built: two hulls and two turrets for firing tests of 88mm, 122mm and 128mm caliber tank guns. The results of these tests were used when developing the final armor profile variant.

The Central Design Bureau of Ordnance also proposed a new S-70 cannon instead of the S-26. This cannon was able to fire 33,4 kg two part AP ammunition with 900 m/s starting shell velocity. The aiming equipment was also improved in order to provide good accuracy when firing at a long range. The second high caliber machinegun was installed on top of the turret, on a special mount. It was controlled remotely and could be fired at both ground and air targets. Two more machineguns were placed in the gun mantlet, two on the sides of the hull and two on the sides of the turret facing forward, eight machineguns in total.

The tank was equipped with an automated fire extinguishing system that could be activated three times. It was installed in the engine compartment.

The IS-7 crew consists of five people – driver, commander, gunner and two loaders. The commander was seated to the right of the gun, the gunner to the left. Loaders were also operating the machineguns.

In the summer of 1948, the Kirov factory produced four tanks. Initial trials showed that despite the weight of the vehicle it can easily reach a top speed of 60 km/h and it has a great off-road capacity. The committee was very impressed by the mobility of the tank.

During further firing tests the IS-7 was proven to be nearly invincible by withstanding fire from a German 128mm gun and its own 130mm. Crew protection tests were conducted on dogs and it showed superb crew survival capabilities in combat. The dogs were seated in place of every crew member during a firing test; all dogs survived and reportedly haven’t felt a thing.

Not everything went perfectly. The tracks of one tank got damaged when a shell bounced off from the angled hull side and hit the chassis. Another tank was set on fire due to an engine failure and the automated fire extinguishing system failed to put it out. The crew got out safely and the tank burned out completely. Still all the trials were passed successfully.

It’s hard to say how good the IS-7 could’ve actually been. The first 50 tanks were never fully produced due to financial problems. The industry just couldn’t afford that and the Soviets focused on producing cheaper medium tanks. Another problem was that the infrastructure for a 68 ton tank just wasn’t there, railroads were not capable of transporting cargo so heavy. All works on IS-7 were soon abandoned.

Surely, “Object 260” had very impressive characteristics and easily outmatched any WW2 vehicle and even its direct competition. In the 50s the British “Conqueror” and American M103 were the most heavily armored and heavily armed tanks in the world. Both tanks had 120mm cannons (L1 and M58 correspondingly), a very powerful armament. The IS-7 was completely invulnerable to these guns frontally and also was smaller and much more mobile (60kph vs. 34kph) while having a similar mass. Anything that could have a hope of defeating the IS-7 was developed only around 70-80s.

The entire concept of a heavy tank was outdated at this point. NATO was formed in 1949 to oppose the USSR and the nature of conflict changed. “The Big Game” now was played with nuclear weapons and aviation while local conflicts were being resolved with cheaper and easier to produce tanks.

The IS-7 was the peak of Soviet heavy tank design. The tank was ahead of its time and embodied lots of extremely potent tank design methods and technologies. But the history wasn’t very kind to this titan, it was forgotten and fell into obscurity, overshadowed by T-10, but that’s a story for another day. One last surviving IS-7 resides on display in the Kubinka Tank Museum near Moscow.

Original article by Nikolay Nevskyi:

All pics are taken from