The six prototype of the IS-4 heavy tank named "Object 701-6".

In 1944, the development of the IS-4 heavy tank (factory designation: IS-4-701) began. It was an attempt to develop a heavy tank for the last period of World War II and for the post-war period.

The production version of the tank was preceded by several prototypes: "Object 701-2", "Object 701-5", and "Object 701-6". These tanks were distinguished by their armament (type and caliber) as well as their armor protection. "Object 701-6" was the most successful, and in 1947 it was accepted for service under the IS-4 designation.

The IS-4 heavy tank.

One of the main features of the new tank was the layout of the ammunition: 30 multi-part loading (separate loading) rounds.

This ammunition was placed in special steel cartridges to protect them from accidental detonation and fire. Today it is widely believed that large-scale production of this tank started in 1947, but some production tanks may have been built in 1945-1946. In total, about 250 IS-4's were manufactured. Most of these tanks were sent to Far East units. In 1949, production was canceled and later these tanks were removed from service. That short operational life was due to:

- The weight of the tank exceeded the carrying capacity of most bridges and transport vehicles;
- Low reliability of the transmission;
- Below average tractability.

The wooden mockup of the IS-5.

This project began in 1944 in Factory #100 which was headed by J.Y.Kotin. There were several variants of this tank which were distinguished by differing armament, protection, and layout of the turret. The chassis was based on an existing project, but it also contained some original ideas. Only wooden scale-models of this tank were produced.

The IS-6 with the mechanical transmission during trials.

In 1954, a new project was developed in Chelyabinsk, called "Object 253". It later received the "IS-6" designation. The main feature of the new tank was an electro-mechanical transmission. The chassis of the new tank was similar to the IS-2.

There was also a tank developed and produced with a mechanical transmission such as on the IS-3. This tank received the "Object 252" designation. The chassis of "Object 252" consisted of big road wheels only (without support wheels). Later, Soviet designers chose the electro-mechanical transmission. The maximum speed of the 51.5-ton tank was 43 km/h.

The firepower of the IS-6 was equal to the IS-2, IS-3 or IS-4. Protection was better than the IS-2 or IS-3, but inferior to the IS-4.

The IS-6 with the electric-mechanical transmission.

Use of the electro-mechanical transmission was expected to increase the maneuverability of the tank. Unfortunately, it did not due to the tank's heavy weight. The transmission was also of questionable reliability. The IS-6 with the purely mechanical transmission was even less reliable.

The wooden model (1:1) of the IS-7. 1946.

In 1945, Soviet designers started a new project: "Object 260" (IS-7). This tank was distinguished from the tanks of World War Two by many features. The hull of "Object 260" was made of sloped armor plates with rakish angles. Only a wooden mockup (1:1) was made.

In 1946, another variant was built. This variant had the same designation ("Object 260"). The first prototype was finished on September 8, 1946, and passed running trials successfully. A second prototype was completed by December 25 of 1946 and also passed running trials (45km).

One of the main features of both prototypes were rubber-and-steel tracks. Such tracks were widely used by the Americans since World War II, but were previously rejected by Soviet designers. The tank was armed with a 130 mm S-26 gun with a new muzzle brake. Rate of fire was 6-8 shots per minute (very high considering the large calibre of the gun). The high rate of fire was due to a new automatic loading mechanism.

The prototype of the IS-7 heavy tank. 1948.

An Izhorsky factory manufactured two armored hulls and two turrets for the IS-7. They were tested at the Kubinka proving ground by gunfire from various guns of 88 mm, 122 mm and 128 mm calibres. The results were used for developing a final scheme of armor protection.

During 1947, Soviet designers worked on a project which was an improved variant of the IS-7. Both hull and turret were redesigned and their armor protection was increased. The tank was rearmed with the newest 130 mm S-70 (L/54) gun. Another new feature was a system of fire control which allowed the gun to lock on a target and fire automatically.

The production IS-7 heavy tank.

In the summer of 1948, the Kirovskiy factory produced four IS-7 tanks. After they passed the factory trials, they were sent for Government trials. The armor protection of the IS-7 was almost invulnerable: the tank successfully withstood German 128 mm and Soviet 130 mm guns (the best guns of that time).

The IS-7 can be considered a masterpiece of Soviet tank development. It was far superior to all other tanks of the time. Having the weight of the "King Tiger" the IS-7 was far superior in protection and armament. The last surviving IS-7 is now displayed at Kubinka.

The first production T-10.

At the end of 1948, the GBTU (General Tank Directorate) issued an order to develop and produce a new heavy tank weighing no more than 50 tons. Work on the new "Object 730" was headed by J.Y.Kotin. That tank later received the "IS-8" designation.

A wooden mockup (1:1) was built and construction of the first prototype of the IS-8 began. After trials, the factory produced a small lot of 10 tanks, a testing detachment. In the spring of 1950 at the Kubinka proving ground, these tanks were tested in government trials. Those trials were more or less successful and, as a result, a Government commission recommended the IS-8 for production, but only after a number of improvements were to be made.

The modifications were so numerous and significant that the project changed course many times. The tank was even renamed to the "IS-9", and then to the "IS-10". In March 1953, Stalin died and the abbreviation "IS" was obsolete. So the tank was renamed again, and it received the new "T-10" designation.

The T-10A on military parade. Red Square, Moscow. November 7, 1957.

The T-10 was armed with a 122 mm D-25TA gun and a coaxial 12.7 mm DShKM machine-gun (a modernised DShK). In 1955 the first two prototypes were produced: "Object 267 sp.1" with gun stabilization in the vertical plane and "Object 267 sp.2" with a 2-plane gun stabilizer. A year later these features were used in a subsequent version, the T-10A ("Object 730A").

In 1957, another modification, the T-10B ("Object 730B") was accepted into service. This tank was equipped with a 2-plane gun stabilizer, the PUOT-2 "Grom" and a T2S-29-14 sight.

Soon, a new 122 mm M-62-T2 (2A17) gun with improved ballistics was developed. This gun was equipped with a 2-plane stabilizer, the 2E12 "Liven" and a T2S-29-14 sight. The new tank ("Object 272") was also equipped with night vision devices. Under the designator T-10M the tank was accepted to service and put into production in 1957.

The T-10M heavy tank.

In 1963 the T-10M was equipped with OPVT - a special system for underwater river crossings (up to 5 metres deep). From 1967, the tanks received APS and HEAT ammunition. The T-10 wasn't exported and was never used in military conflicts. In 1966, the manufacture of the T-10 was canceled. In 1993, the T-10 heavy tank was removed from Russian Army service.

"Object 277" during trials.

In 1957, "Object 277" was developed by J.Y.Kotin's design bureau. The new tank was based on ideas from the IS-7 and the T-10. "Object 277" was armed with a 130 mm M-65 gun and coaxial 14.5 mm KPVT machine-gun. The gun was equipped with a "Groza" 2-plane stabilizer and a night vision system. Ammunition consisted of 26 shells for the main gun and 250 rounds for the machine-gun. The tank had a diesel engine of 1,090 hp.

The "Object 277" was equipped with an anti-nuclear defense system, a system of clearing the sights and a system for underwater river crossings. The crew consisted of four men, and the tank had good maneuverability. Two tanks were built in 1958.

The "Object 279" during trials. 1959-1960.

In 1957, a group of engineers, headed by L.S.Troyanov, developed a prototype of a new heavy tank, named "Object 279". This was a very unique vehicle. The tank had a classic layout, but the problem of protection was solved by an unusual design feature. The hull of the tank was covered by a thin elliptical shield. That shield protected the tank against HEAT ammunition and to prevent it from overturning during a nuclear explosion.

The thickness of the glacis plate was 269 mm, and the thickness of the turret was 305 mm. The tank was armed with a 130 mm M-65 gun and a coaxial 14.5 mm KPVT machine-gun. The ammunition carried for the main gun was 24 shells. The Engine was a 16-cylinder diesel DG-1000 (950 hp) or 2DG-8M (1000 hp). The tank's crew consisted of four men.

Another unusual feature of the tank was the chassis. It consisted of four tracks combined in pairs. Such construction increased the tank's height, but guaranteed that the tank would rarely get bogged down. The tank also had great tractability on snowy and swampy terrain. At the end of 1957, a single tank had been built, but after that the project was abandoned. The "Object 279" is now displayed at Kubinka.

The "Object 770" during trials. The chassis of the "Object 770". Kubinka.

Unlike "Object 277", this tank was based on several unique ideas. The tank was equipped with a nuclear defence system, automatic fire-extinguisher system, night vision equipment, and semi-gyrocompass.

The thickness of the glacis plate was 120 mm, and the turret was 290 mm thick. Armament consisted of a 130 mm gun M-65 and one 14.5 mm machine-gun KPVT. The amount of ammunition carried for the main gun was 26 shells and 250 rounds were carried for the machine-gun. The engine was a 10-cylinder diesel DTN-10 (1000 hp) with a water-cooling system. The crew consisted of four men.

Having very good maneuverability, this tank was very easy to control. In a Soviet tank expert's opinion, "Object 770" was one of the most exemplary vehicles of the time. Today "Object 770" is displayed at Kubinka.