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Iosif Stalin Tank
Home > Tanks > IS Tank Series
modified: Nov 10, 2012
The Iosif Stalin tank (IS tank, also called JS tank, ИС танк) is a series of Soviet heavy tanks named after Joseph Stalin and developed during the Great Patriotic War. They were based on the KV-13 heavy tank. The IS -3 was viewed as the most potent tank of its time.

The IS tank series has its origins in the KV-13. Kotin's design team was experimenting with new suspensions, hull layouts and turrets by constructing various variants of the KV-13. One example is the KV-1S which was upgraded to an 85mm D-5T gun and designated the KV-1S-85. However, the turret of this new prototype was not large enough for the 85mm gun and its recoil.

Based on the KV-13 research, a new tank codenamed izdeliye 237 (Item 237) emerged. This tank had an 85mm gun and armor thickness similar to that of the KV-1 Model 1942. Since the hull and turret were redesigned as well as transmission and power-train upgrades being introduced, izdeliye 237 was almost as mobile as the KV-1S. Stalin and GKO members viewed the prototype in August 1943. It was approved under the designation IS-85 and production began in September 1943. A total of 67 IS-85s were completed by the end of 1943 with an additional 40 being built at the beginning of 1944.

Firing trials of the 85mm D-5T gun on captured German Tiger I tanks were conducted at Chelyabinsk. The 85mm gun had to be within the Tiger I's own 88mm gun range in order to reliably penetrate the German tank.

The Kirovsky Factory adapted the 100mm BS-3 anti-tank gun to the IS-85 with the designation IS-100. It also adapted the 122mm A-19 gun under the name IS-122 heavy tank (Izdeliye 240, IS-2 Model 1943). Firing trials were conducted on a captured Panther at NIIBT in November 1943. Although the 100mm gun demonstrated better armor penetration, the 122mm gun was favored due to the surplus of 122mm tube production facilities and sufficient ammunition base. However, a few IS-85s were armed with 85mm guns before the 122mm gun was selected. When the IS-122 was approved by the GKO, the IS-85s were re-gunned before entering service.

For security purposes, izdeliye 237 was designated the IS-1 and izdeliye 240 became the IS-2. In 1943, in addition to the prototypes, 102 IS-2s were manufactured. Demand for the IS-2 was so high that the NKTP began the construction of a new assembly facility at Tankograd.

The IS-2's first combat use was with the 11th Guards Heavy Tank Regiment in April of 1944. The regiment, commanded by Col. Tsiganov fought several skirmishes with the Tiger I tanks of the s.Pz.Abt. 503 near Tarnopol. A single IS-2 was destroyed before the Germans quickly retreated.

The new hull of the IS-2 provided a better ballistic protection compared to the KV. The stepped armor glacis plate of the IS-1 was replaced with a flat sloping type which improved protection without increased thickness. It was able to withstand a German 88mm armor-piercing round at over 1000m. The new anti-tank gun had 3.5 times more kinetic energy on impact than the 76mm gun. It's gun can penetrate 160mm armor from a range of 1000m. However, the small turret volume allowed stowage of only 28 rounds. These were of the split type slowing the rate of fire to 2 or 3 rounds per minute. The turret was retained due to the cost of replacement and lack of time. A total of 2,250 IS-2s were built.

The IS-2 underwent improvements in the spring of 1944 becoming the IS-2m (m: modifikatsirovanniy)(IS-2 Model 1944). The major change was the implementation of the new and simpler angled bow casting. The fire control was improved and internal changes were also made. The D-25T gun, which was similar to the A-19 save for the its drop-breech which quickened loading, was also introduced. Also during this time, experimental versions of the IS-2 were built. The IS-1E variant for example, had new electrical transmission and a new road wheel arrangement. However, none of these experimental versions were accepted.

While experiments were conducted on the IS-2, a team under Dukhov at TsKB-2 was created to examine the re-configured IS-2. One new version was the IS-3 with a new hemispherical turret and the other - IS-4 with a longer hull and thicker armor.

The design of the IS-3 incorporated ideas from two teams. Kotin's team developed a frontal armor glacis consisting of two plates welded together at an angle, sloping down the vehicle's front. This reduced the tank's weight and increased hull strength and resistance to enemy fire. N.L. Dukov's team developed a heavily-rounded turret armored with a 122mm gun. The shape of the turret increased protection by deflecting the kinetic energy of shells and also improved the internal layout. Minister of Tank Industry, V.A. Malyshev, decided to incorporate both ideas. The IS-3 also had large stowage bins attached to the side hull over the tracks.

In October 1944, the first prototype was shown to Marshals G.K. Zhukov and A.M. Vasilevsky and was approved for production. The first production models appeared in early 1945. About 350 IS-3 were produced concurrently with the IS-2m.

Although official Soviet accounts indicate that the IS-3 saw combat towards the end of the war in Germany, internal Soviet histories and heavy tank designers contradict this claim. The IS-3 was known as Shchuka (Pike) due to its pointed bow. The IS-3 was similar to the IS-2m except for the armor layout. The IS-3 was considered the most advanced and powerful heavy tank of its time. Production of the IS-3 lasted until 1951 at Chelyabinsk with about 1800 built. The shape of IS-3 influenced later Soviet tanks as well as Western designs.

The IS-3 remained in Soviet Army service until the 1960s while undergoing modifications to improve unreliable engine and gearbox, and a hull that was defective in some areas. However, modifications were partially successful and Soviet tank doctrine was favoring the medium tank as the main armored vehicle.

L.S. Troyanov's design team was working on a new version of the IS-2 under the codename Obiekt 701. Three designs were presented to the Red Army's tank directorate. Obiekt 701-2 was armed with the 100mm S-34 gun. Obiekt 701-5 had a different armor configuration. And Obiekt 701-6 mounted the standard 122mm D-25T gun with thicker armor and lengthened hull. The Obiekt 701-6 design was selected for further development. The basic armor for the hull was increased to 160mm and the turret to 250mm. The 750hp V-12 engine had a revised cooling system. In 1947, Obiekt 701-6 was accepted for series production as the IS-4.

IS-4 production was stopped after only 200 units had been built due to the poor speed and mobility of the vehicle. During the Korean War, almost all IS-4 regiments were sent to the Far East where they would form the shock force for a tank army. However, Stalin chose not to intervene in the conflict. The IS-4s remained in the region and stayed in service until the 1960s. They were modernized in the late 1950s along the same lines as the IS-3M.

IS-2M and IS-3M
The IS-2 and IS-3 underwent improvements after the Second World War. In 1954, IS-2s began to be rebuilt as the IS-2M. Main gun ammunition was increased from 28 to 35 rounds. The improved V-54K-IS engine was used with a modernized engine cooling and oil flow system. New radios and intercoms as well as an improved driver's periscope were included. Stowage was increased by adding tool bins on the front hull side. Dirt skirts were also added.

The IS-3 modernization program began in 1960. It included hull reinforcement, replacement of the 12.7mm DShK machine gun with the DShKM, and addition of a driver's TVN-2 night vision. The V-54K-IS engine was used with the Mutlitsiklon air filter system. New wheels with improved ball-bearings were added from the T-10 heavy tank. Dust skirts were added over the suspension as well as an increase in external stowage. The IS-3M took part in the 1956 Hungarian Revolution against insurgent forces.

After the Second World War, the SKB-2 design bureau was divided into several teams at the Chelyabinsk plant and the reopened Kirov Plant. There were three different designs that were being developed. The main Kotin team used IS-4 components while focusing on the advantages of an electrical transmission. This project was called Obiekt 703.

Electrical transmissions offered more usable power to the tracks, improved steering and mobility. During the Second World War, a test-bed, called the IS-1E, was built on a IS-1 chassis. The Obiekt 703 transmission was based on a 385kW DK-305A generator. Although the project was redesignated the IS-6, it was not suitable for mass production. In the first day of its trials, the prototype burst into flames just after exiting the hangar.

The electrical transmission required too much cooling. Izdeliye 252 was an effort to recover the design by using the IS-4 mechanical transmission. However, the project was terminated since it did not provide any advantages over existing tanks.

Concurrent with the development of the IS-6, Nikolai Shashmurin's team was working on a new tank designated the IS-7. However, this design did not resemble any Soviet heavy tank. Shashmurin incorporated components developed by Soviet naval research institutes. The tank was powered by a 1050hp marine diesel engine. It mounted a 130mm gun derived from the 56-SM naval gun. This gun was the most powerful weapon to be mounted on a Soviet tank up to that point.

Secondary armament included a 14.5mm KPVT coaxial heavy machine gun. In addition, six 7.62mm machine guns were provided, two coaxially in the mantlet, two on the right side of the hull, and the last two on either side of the turret in small armored barbettes. An additional 14.5mm KPVT heavy machine gun was located in a remote control mount on the roof to serve in the antiaircraft role.

The IS-7 was the heaviest Soviet tank ever built weighing in at 68 tonnes. Due to its powerful engine, the IS-7 could attain higher road speeds than previous Soviet heavy tanks. The IS-7 firepower and armor matched those of NATO tanks in the 1960s. The suspension employed internal shock absorbers in the wheels based on the German Tiger II.

The first IS-7 prototype was completed in 1948. The tank was criticized for its extremely cramped space, heavy ammunition, and excessive number of machine guns. The shock absorbers were quickly worn out and caused breakdowns when the tank was operated at top speed. The great weight of the IS-7 would strain the Soviet rail and road network as well as requiring high initial and maintenance costs. Only a few test IS-7s were built.

The IS-8 used many components from the experimental IS tanks. The electrical turret traverse and elevation, and the short torsion bar suspension were based on that of the IS-7. The V-12-5 engine was derived from the IS-4 and IS-6. The tracks were taken from the IS-4. The D-25TA gun was an improved version of the one on the IS-2 and IS-3. The new 122mm BR-472 ballistic-capped projectiles which have better penetration than the BR-417B were used.

The basic turret armor was raised to 200mm. Improved engine cooling was achieved by boosting the airflow through the radiators using exhaust gases. The hull was lengthened and had an additional set of road wheels similar to the IS-4.

Production began at Chelyabinsk in late 1950 or early 1951. Production may have also been extended to the tank plant in Omsk.

During the period of De-Stalinization, the IS-8 was redesignated the T-10. The T-10A mounted the new D-25TS gun with a stabilization system in the vertical axis as well as a bore evacuator. The T-10A had a simple rammer to assist the gunner. The gunner loaded the projectile and casing on a tray and the rammer pushed them into the breech. A new TPS-1 periscopic sight and a TUP telescopic sight replaced the Tsh-2-27 sight. A TVN-1 night vision device for the gunner and a GPK-48 gyrocompass were also added.

The T-10B was the next variant that emerged in the mid 1950s. This version had a two-axis stabilization system for the gun and T2S-29 fire control sights.

The T-10M, introduced in 1957, was the final variant. The most significant improvement was the use of the M-62-TS gun which had better armor penetration. This gun could fire the BP-460A HEAT projectile. The M-62-TS gun was fitted with the Liven two-axis stabilization system and had a distinguishable multi-slotted muzzle brake.

Other modifications on the T-10 include the replacement of both the 12.7mm DShK coaxial and anti-aircraft machine guns with 14.5mm KPVT heavy machine guns. The T-10M was powered by a 750hp V-12-6 engine. Production of the T-10 ended in 1962. About eight thousand units of all variants were produced which makes the T-10 quantitavely the most significant of the Stalin tank series.

Assault Guns
Several assault gun variants were based on the IS tank series. These include the ISU-152 and ISU-122.

References: EWWW2, IHT, OW, RTWW2, STCV, TBOT, WW2T
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