IS tank family

Iosif Stalin tank
Heavy Tanks Evolution USSR.jpg
Evolution of some selected vehicles of the Soviet heavy tanks lineage (KV-1 to T-10M).
TypeHeavy tank
Place of originSoviet Union
Service history
Used bySoviet Union, China, Cuba, Czechoslovakia, DPRK, Egypt, Poland
Production history
DesignerZhozef Kotin
Nikolay Dukhov
  • 1943 (IS-2)
  • 1944 (IS-3)
  • 1944–45 (IS-4)
ManufacturerKirov Factory, UZTM
Unit costIS-2 Model 1944: 264,400 rubles[1]
  • 1943–44 (IS-1)
  • 1943–45 (IS-2)
  • 1945–47 (IS-3)
  • 1947–49 (IS-4)
No. built
  • 130 (IS-1)
  • 3,854 (IS-2)
  • 2,311 (IS-3)
  • 250 (IS-4)
Specifications (IS-2 Model 1944[2])
Weight46 tonnes (51 short tons; 45 long tons)
Length9.90 m (32 ft 6 in)
Width3.09 m (10 ft 2 in)
Height2.73 m (8 ft 11 in)

ArmorIS-2 Model 1944:
Hull front: 100 mm at 60° angle
Lower glacis: 100 mm 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.
D25-T 122 mm gun (28 rounds)
DShK, 3×DT (2,079 rounds)
Engine12-cyl. diesel model V-2
600 hp (450 kW)
Power/weight13 hp/tonne
Suspensiontorsion bar
Fuel capacity820 l (180 imp gal; 220 US gal)
240 km (150 mi)
Speed37 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).

Design and production

Object 237 KV-85 and IS-85/IS-1

The KV-85 was a stop-gap solution until the introduction of the IS series. Note the modified KV chassis with the removal of the hull machine-gunner/radio operator's station with one operated by the driver, and the driver's station slightly centered at the front; a staple design of all IS-series tank.
IS-85 (IS-1) Prototype equipped with D-5T gun. Later IS-2 converted models were replaced with the 122mm D-25T gun whilst retaining the same hull.

The KV-1 was criticized by its crews for its poor mobility and the lack of a larger caliber gun 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.[3] 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[4] and ended in April 1943.[5]

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.[6] 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 stopgap 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 series.[7]

The Object 237 prototype, a version of the cancelled KV-13, was accepted for production as the IS-85 heavy tank.[8] First deliveries were made in October 1943, and the tanks went immediately into service. Production ended in January 1944. Its designation was simplified to IS-1 after the introduction of the IS-122, later renamed as IS-2 for security purposes.[9]

Object 240 IS-2


By 1943, engineers had succeeded in mounting the 85 mm gun to the T-34 medium tank, making it as well-armed as the KV-85 heavy tank. Efforts to up-gun the IS-85 began in late 1943. Two candidate weapons were the D-25 122 mm tank gun, the ballistic characteristics of which were identical to the A-19 122 mm gun,[10] and the D-10 100 mm gun, which was based on a naval dual-purpose gun. The D-10 had been designed for anti-tank fire and had better armor penetration than the A-19, but the smaller caliber meant it had a less useful high explosive round. Also, the D-10 was a relatively new weapon in short supply, while there was excess production capacity for the A-19 and its ammunition. Compared to the older F-34 76.2 mm tank gun, the D-25 delivered 5.37 times the muzzle energy.

After testing both the D-25 and D-10 on the IS-122, the former was selected as the main armament of the new tank. The D-25 used a separate shell and powder charge, resulting in a lower rate of fire compared to the single-piece ammunition used in most tanks, a serious disadvantage in tank-to-tank engagements. Soviet proving-ground tests showed that the D-25 could penetrate the front armor of the German Panther tank at 2,500 m (2,700 yd) while the D-10 could do so at a maximum range of 1,500 m (1,600 yd).[10][11] It was therefore considered an adequate anti-tank gun.

Projectiles and charges of the separate-loading ammunition of the A-19/D-25T 122mm gun. Left to right: cartridge case, high-explosive/fragmentation shell OF-471, armor-piercing high explosive shell BR-471, armor-piercing ballistic capped shell BR-471B. All shells are shown from two sides.

A Wa Pruef 1 Report dated 5 October 1944 has data on the penetration ranges of the 122 mm A-19 gun against a Panther tank angled at 30 degrees; this estimated that the A-19 gun was unable to penetrate the upper glacis plate of the Panther from any distance, could penetrate the lower glacis plate from 100 m (110 yd), could penetrate the mantlet from 500 m (550 yd) and could penetrate the front turret from 1,500 m (1,600 yd).[12] The Panther's 40–50 mm (1.6–2.0 in) thick side armor would have been exposed and vulnerable at such an angle; the sides at 30 degrees were penetrable from over 3,500 m (3,800 yd) according to the same Wa Pruef 1 report.[12] Testing with captured Tiger Ausf Bs in Kubinka showed that the 122 mm D-25T was capable of penetrating the Tiger Ausf B's turret from 1,000–1,500 m (1,100–1,600 yd) and the weld joint or edges of the front hull plates at ranges of 500–600 m (550–660 yd).[13] In 1944, the BR-471 was the sole armor-piercing round available. An improved version, the BR-471B (Russian: БР-471Б) was developed in spring 1945, but was available in quantity only after World War II ended.[14]

According to the same Wa Pruef 1 report, it was estimated that at 30 degree obliquity the hull armor of the Soviet IS-2 model 1943 would be defeated by Tiger I between 100 and 300 m (0.062 and 0.186 mi) at the driver's front plate and nose,[15] while the IS-2's 122 mm gun would penetrate the Tiger's front armor from between 500 and 1,500 m (0.31 and 0.93 mi).[15] A Panther had to close to 600 m (660 yd) to guarantee penetration of the IS-2's frontal armor (The Panther's 75 mm gun could penetrate the IS-2 model 1943's mantlet from 400 m (440 yd), front turret from 800 m (870 yd), and driver's front plate from 600 m (660 yd)[16]), while the IS-2 could penetrate the Panther at ranges of 1,000 m (1,100 yd).[17][Notes 1] However, in the summer of 1944, the Germans experienced a shortage of manganese and had to switch to using high-carbon steel alloyed with nickel, which made armor very brittle, especially at the seam welds. The performance of the 122 mm AP shells of the IS-2 against the Panther improved considerably. The reports from the front described cases where the BR-471 APHE round 122 mm projectile fired from 2,500 m (2,700 yd) ricocheted off the front armor of a Panther, leaving huge breaches to it.[18][unreliable source?] According to Steven Zaloga, the IS-2[17] and Tiger I could knock each other out in normal combat distances below 1,000 m (1,100 yd). At any range, the performance of each tank against each other was dependent on the crew and combat situation.[19]

Line drawing of IS-2

The large 122 mm HE shell was its main asset, proving highly useful and destructive as an infantry-killer. In extremis, the IS-2 engaged enemy heavy armor with OF-471 (Russian: ОФ-471) high explosive projectiles. These shells had a mass of 25 kg (55 lb), a muzzle velocity of 800 m/s (2,600 ft/s), and were equipped with a 3.8 kg (8.4 lb) TNT charge. The explosive power could blow off an enemy tank turret, drive sprocket and tread of the heaviest German tank even if it could not penetrate the armor.[20][21][20][21] Mechanical shock and explosion was often enough to knock out enemy heavy tanks.[20]

The most recognizable disadvantage of the D-25T gun was its slow rate of fire due to the large size and weight of the shells; only one to one and a half rounds per minute could be fired, initially.[22] After some design improvements, including a semi-automatic drop breech over the previously manual screw breech, the rate of fire increased to 2–3 rounds per minute.[22], and according to other sources, the increase may have amounted to 3–4 rounds per minute.[23] Another limitation imposed by the size of its ammunition in a relatively small vehicle was the ammunition stowage: only 28 rounds could be carried inside the tank, with a complement of 20 HE rounds and 8 AP rounds the norm.[24][25]


The IS-122 prototype replaced the IS-85 and began mass production as the IS-2. The 85 mm guns could be reserved for the new T-34-85 medium tank and some of the IS-1s built were rearmed before leaving the factory and issued as IS-2s. It was slightly lighter and faster than the heaviest KV model 1942 tank, with thicker front armor and a much-improved turret design. The tank could carry thicker armor than the KV series, while remaining lighter, due to the better layout of the armor envelope. The KV's armor was less well-shaped and featured heavy armor even on the rear, while the IS series concentrated its armor at the front. The IS-2 was slightly lighter than the Panther, much lighter than the Tiger I and Tiger II and had a lower silhouette than both. Western observers tended to criticize Soviet tanks for their lack of finish and crude construction. The Soviets argued that it was warranted, considering the need for wartime expediency and the typically short battlefield life of their tanks.[26]

Armor plan of IS-2, models 1943 (top) and 1944 (bottom).

Early IS-2s can be identified by the 'stepped' front hull casting with its small, opening driver's visor. The early tanks lacked gun tube travel locks or anti-aircraft-capable machine guns and had narrow mantlets.

In late 1944, the stepped hull front was replaced with an improved single casting of 120 mm thickness angled at 60 degrees. This new nose lacked the opening driver's visor. It is sometimes incorrectly referred to as the IS-2M, but that designation actually refers to a much later modernization program from the 1950s. Other minor upgrades included the addition of a travel lock on the hull rear, wider mantlet and, on very late models, an anti-aircraft machine gun.

In comparison to the Tiger I, the IS-2 had modest advantages in armour, even though it was 10 tons lighter[27]

In the mid-1950s, the remaining IS-2 tanks (mostly model 1944 variants) were upgraded to the IS-2M standard, which introduced fittings such as external fuel tanks on the rear hull (the basic IS-2 had these only on the hull sides), stowage bins on both sides of the hull and protective skirting along the top edges of the tracks.

Object 703 IS-3


There are two tanks known as IS-3: Object 244 was an IS-2 rearmed with the long-barrelled 85 mm cannon (D-5T-85-BM) and developed by LKZ (in Leningrad), which was never series-produced for service use.

Object 703 was developed in late 1944 by ChTZ (in Chelyabinsk) and left the factory shop in May 1945.[28] This tank had an improved armour layout, and a semi-hemispherical cast turret (resembling an upturned soup bowl), which became the hallmark of post-war Soviet tanks. While this low, hemispherical turret improved protection, it also significantly diminished crew headroom, especially for the loader. The low turret also limited the maximum depression of the main gun, since the gun breech had little room inside the turret to elevate, and this limited the extent to which the IS-3 could take advantage of hull-down positions.[29] The IS-3's pointed prow earned it the nickname Shchuka (Pike) by its crews. It weighed slightly less and stood 30 centimetres (12 in) lower than previous versions. Wartime production resulted in many mechanical problems and a hull weldline that had a tendency to crack open.[30]

The IS-3 came too late to see action in World War II. The first public demonstration of the IS-3 came on 7 September 1945 during the Allied victory parade on Charlottenburger Straße in Berlin, with the heavily reinforced 71st Guards Heavy Tank Regiment of the 2nd Guards Tank Army.[28] Starting in 1960, the IS-3 was slightly modernized as the IS-3M, in a manner similar to the IS-2M.

Object 701 IS-4


There are two tanks known as IS-4: Objekt 245 and Objekt 701. Objekt 245 was an IS-2 rearmed with a long 100 mm D-10T cannon. The other IS-4 was a new vehicle projected by LKZ in parallel with the IS-3 known as Objekt 701 by the same design and development bureau. For the latter, the IS-2 hull was lengthened, with an extra set of road wheels added and an improved engine. Both hull and turret armor were increased. Several alternative armaments were explored in paper studies but ultimately the IS-2's original 122 mm gun was retained. An effort was also made to make use of technical data derived from study of the German wartime Panzer V Panther tank, which influenced the layout of the Objekt 701's engine cooling system. The tank was approved for mass production from 1947 to 1949 but, due to disappointing speed and mobility, only 250 were built. Most of these were transferred to the Russian Far East. In 1949, production was cancelled and later these tanks were removed from service.

Object 252/253 IS-6

There existed two different IS-6s: the Object 253 was an attempt to develop a practical electrical transmission system for heavy tanks. Similar systems had been tested previously in France and the United States and had been used with some success in the German Elefant/Ferdinand tank destroyer during World War II. The experimental transmission proved unreliable and was dangerously prone to overheating, and development was discontinued. The alternative Object 252 shared the same hull and turret as the Object 253, but used a different suspension with no return rollers, and a conventional mechanical transmission. The design was deemed to offer no significant advantages over the IS-2, just the reload time was less, and the IS-6 project was halted.

Object 260 IS-7

An IS-7 tank during trials (1948)

The IS-7 heavy tank was developed in 1948.[31][32] Weighing 68 tonnes, thickly armoured and armed with a 130 mm S-70 long-barrelled gun, it was the largest and heaviest member of the IS family.[33]

The armour was engineered in a similar fashion to the IS-3, with a pike nose on the upper glacis. When shot at frontally, the extreme angle that the pike nose presents results in a much higher likelihood of a ricochet. Thus, the armour protection could be enhanced without having to use excessive amounts of materials. However, if the pike nose was shot at a sideways angle, it would not have a relative thickness high enough to ricochet the shell. In spite of its weight, it was easy to drive due to numerous hydraulic assists. The loaders noted that the IS-7 was comfortable and that the autoloader was easy to use. It was also able to achieve a top speed of 60 km/h thanks to a 1050-horsepower engine giving it a power to weight ratio of 15.4 hp/tonne, a ratio superior to most contemporary medium tanks. Its armour was not only immune to the Jagdtiger's 12.8 cm Pak 44 but was even proof to its own 130mm. Due to the reasons unknown, most likely because of the considerable issues arising from its mass (bridges, rail transport - no Soviet/Russian tank accepted into service afterwards exceeded 55 t), the tank never reached the production lines.[34][unreliable source?]

Object 730 T-10

The IS-10[35] (also known as Objekt 730) was the final development of the KV and IS tank series. It was accepted into service in 1952 as the IS-10,[35] but due to the political climate in the wake of Stalin's death in 1953, it was renamed T-10.

The biggest differences from its direct ancestor, the IS-3, were a longer hull, seven pairs of road wheels instead of six, a larger turret mounting a new gun with fume extractor, an improved diesel engine, and increased armour. General performance was similar, although the T-10 could carry more ammunition.

T-10s (like the earlier tanks they replaced) were deployed in independent tank regiments belonging to armies, and independent tank battalions belonging to divisions. These independent tank units could be attached to mechanized units, to support infantry operations and perform breakthroughs.

The T-10M is the final iteration of this type. It featured a longer gun barrel than previous models with 5-baffle muzzle brake and 14.5 mm machine gun. This was the last Soviet heavy tank to enter service. When the advanced T-64 MBT became available it replaced the T-10 in front line formations.


Soviet heavy tanks of World War II[36]
T-35 T-100 SMK KV-1
M1945[clarification needed]
IS-3[37][unreliable source?][38]
Crew 11 7 7 5 5 5 5 4 4 4
Weight (tonnes) 45 58 55 43 45 47 42.5 46 46 46.5
Gun 76.2 mm
M. 27/32
76.2 mm
76.2 mm
76.2 mm
76.2 mm
76.2 mm
76.2 mm
85 mm
122 mm
122 mm
Ammunition 100 111 111 114 114 70 28 28
Secondary armament 2×45 mm
5×7.62 mm
45 mm 45 mm DT 4×DT 4×DT 4×DT 3×DT 3×DT, DShK 2×DT, DShK
Engine 500 hp
M-17M gasoline
500 hp 850 hp
600 hp
V-2K diesel
600 hp
600 hp
600 hp
600 hp
600 hp
600 hp
Fuel (litres) 910 600 600 600 975 975 820 520 + 270
Road speed (km/h) 30 35 36 35 35 28 45 40 37 37
Road range (km) 150 150 335 335 250 250 250 240 150 (225)
Armor (mm)[clarification needed] 11–30 20–70 20–60 25–75 30–90 20–130 30–82 30–160 30–160 20–220
Other Languages
azərbaycanca: İosif Stalin Tankı
български: ИС (танк)
čeština: IS (tank)
Deutsch: IS-Serie
Bahasa Indonesia: IS (famili tank)
Lëtzebuergesch: Iosif Stalin Tanks
Nederlands: IS-serie
српски / srpski: IS tenkovi
українська: ІС (танк)
Tiếng Việt: Xe tăng Iosif Stalin