[6] They were mainly designed as breakthrough tanks, firing a heavy high-explosive shell that was useful against entrenchments and bunkers.

The IS-3 served on the Chinese-Soviet border, the Hungarian Revolution, the Prague Spring and on both sides of the Six-Day War.

The 1944 model was produced with a revised front slope that was better from an armor point of view while still saving weight.

"[7] 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 the Leningrad Kirov Plant (LKZ), which was never series-produced for service use.

Its semi-hemispherical cast turret (resembling an upturned soup bowl), became the hallmark of post-war Soviet tanks.

[8] 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 limited success in the German Elefant/Ferdinand tank destroyer during World War II.

[citation needed] The IS-7 heavy tank design began in Leningrad in 1945 by Nikolai Fedorovich Shashmurin[9][10] and was developed in 1948.

[11][12] 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.

[15] 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.

The IS-2 was best used for bunker assault using its high-explosive ammunition, as its reload rate, just 2 rounds per minute, made it ineffective as a tank destroyer.

The IS-3 saw service on the Chinese-Soviet border, the Soviet invasion of Hungary, the Prague Spring and on both sides of the Six-Day War.