IS tank family

Iosif Stalin tank
IS-2 model 1943 (fore) and IS-3 at the Great Patriotic War Museum, Minsk, Belarus
Type	Heavy tank
Place of origin	Soviet Union
Service history
Used by	Soviet Union, China, Cuba, Czechoslovakia, DPRK, Egypt, Poland
Wars	World War II*Hungarian Revolution of 1956*Six Day War*Warsaw Pact invasion of Czechoslovakia*War in Donbass
Production history
Designer	Zh. Kotin, N. Dukhov
Designed	1943 (IS-2) 1944 (IS-3) 1944–45 (IS-4)
Manufacturer	Kirov Factory, UZTM
Produced	1943–44 (IS-1) 1943–45 (IS-2) 1945–47 (IS-3) 1945–46 (IS-4)
No. built	130 (IS-1) 3,854 (IS-2) 2,311 (IS-3) 250 (IS-4)
Specifications (IS-2 Model 1944)
Weight	46 tonnes (51 short tons; 45 long tons)
Length	9.90 m (32 ft 6 in)
Width	3.09 m (10 ft 2 in)
Height	2.73 m (8 ft 11 in)
Crew	4
Armor	IS-2 Model 1944: Hull front: 100mm at 60° angle Lower glacis: 100mm at 30° angle Turret front: 100 mm (rounded) Mantlet: 155 mm (rounded) Hull side: 90 - 130 mm at 9-25° Turret side: 90 mm at 20° angle.
Main armament	D25-T 122 mm gun (28 rounds)
Secondary armament	3 × DT (2,079 rounds)
Engine	12-cyl. diesel model V-2 600 hp (450 kW)
Power/weight	13 hp/tonne
Suspension	torsion bar
Fuel capacity	820 l (180 imp gal; 220 US gal)
Operational range	240 km (150 mi)
Speed	37 km/h (23 mph)

The IS Tank was a series of heavy tanks developed as a successor to the KV-series by the Soviet Union during World War II. The heavy tank was designed with thick armor to counter German 88 mm guns and carried a main gun capable of defeating Tiger and Panther tanks. It was mainly a breakthrough tank, firing a heavy high-explosive shell that was useful against entrenchments and bunkers. The IS-2 went into service in April 1944 and was used as a spearhead by the Red Army in the final stage of the Battle of Berlin. The IS acronym is the anglicized initialism of Joseph Stalin (Ио́сиф Ста́лин, Iosif Stalin).

The KV-1 was criticized by its crews for its poor mobility and the lack of a gun heavier than the T-34 medium tank. It was much more expensive than the T-34, without having greater combat performance. Moscow ordered some KV-1 assembly lines to shift to T-34 production, leading to fears that KV-1 production would be halted and the SKB-2 design bureau, led by Kotin, closed. In 1942, this problem was partially addressed by the KV-1S tank, which had thinner armor than the original, making it lighter and faster. It was competitive with the T-34 but at the cost of no longer having the heavier armor. Production of the KV-1S was gradually replaced by the SU-152 and ended in April 1943.

The capture of a German Tiger tank in January 1943 led to a decision to develop a new heavy tank, which was given the codename Object 237. Before Object 237 had time to mature, intense tank fighting in the summer of 1943 demanded a response. Dukhov's team was instructed to create a KV tank, the KV-85, which was armed with the 52-K-derivative gun of the SU-85, the 85 mm D-5T, that proved capable of penetrating the Tiger I from 500 m (550 yd). The KV-85 was created by mounting an Object 237 turret on a KV-1S hull. To accommodate the Object 237 turret, the KV-1S hull was modified, increasing the diameter of the turret ring with fillets on the sides of the hull. The radio operator was replaced with an ammunition rack for the larger 85 mm ammunition. The hull MG was then moved to the opposite side of the driver and fixed in place to be operated by the driver. From September to October 1943, a total of 130 KV-85s were produced, before the assembly lines began to shift over. Like the KV-1S, the KV-85 served in dwindling numbers and was quickly overshadowed by the superior IS Stalin series.