During World War II, the Soviet Iosef Stalin (IS) tank was developed to replace the KV heavy tank. The new heavy tanks proved a success during the war, and went on to set the template for Soviet tanks for decades. Below are some interesting about the IS tanks, the formidable heavy tanks with which the Red Army closed WWII.

The Red Army vs German Tiger Tanks

The standard Soviet heavy tank when it joined WWII was the KV. In 1941, the standard antitank gun on Germany’s dedicated armor-killing tank, the Panzer III, was 37mm. That was puny when facing KV tanks, which simply shrugged off the Panzer III’s shots. The Germans quickly upped their firepower. They upgraded their Panzer IVs with more powerful guns that had greater penetration ability against armor. Then in 1942, they rushed the Panzer VI Tigers into service with powerful 88mm guns.

Against the Tigers’ thick armor, especially up front, the Soviets discovered that their KV’s 76.2mm gun was largely ineffective. Moreover, the slow KVs were unable to maneuver and close in on the enemy quickly, like the Red Army’s T-34s medium tanks could, in order to fire at the Tigers from closer ranges and at weaker spots so as to inflict damage. Something had to be done – and done quickly.

The Need for a New Heavy Tank

The KV had a weak gun that could not damage the German heavy tanks. Simultaneously, its armor that could be penetrated by the Tigers from long range. Thus, the rationale for the KV disappeared. It was far more expensive than the T-34, but lacked greater combat performance to justify the greater cost. To cope with the tougher threat environment while fulfilling the KV’s designated role as a breakthrough tank, the IS line was designed with thick sloped armor to counter 88mm shells.

The Iosef Stalin tanks had thicker armor than the KV. However, because of a better layout, they were lighter and faster than KVs, as well as lighter than Tigers and Panthers, and had a lower silhouette. IS tanks were equipped with powerful guns that, while intended primarily to fire high explosive shells at infantry strong points and bunkers, were also capable of taking out Tigers and Panthers.

The Arrival of the Iosef Stalin (IS) Tanks

The IS line was born from an interim evaluation tank, a KV armed with an 85mm gun. The increased firepower was good, but the KV’s armor was inadequate. So the Red Army issued directives for a new tank design to be armed with an 85mm gun, but with better armor than the KV. The result was the IS-1, which entered service in 1943.

The new heavy tank kept the KV’s running gear and hull, but had greater armored protection thanks to a welded turret, and was armed with an 85mm gun. In 1944, IS-1s were succeeded by the IS-2, armed with a 122mm gun that had separate shell and powder charges. That resulted in a slow rate of fire of only 1.5 rounds a minute initially, later improved to 3 or 4 rounds.

The IS vs German Heavy Tanks

The huge shells and powder charges meant that fewer could be stored inside the IS-2s, which were limited to 28 shells on board, usually a mix of 20 high explosive, and 8 antitank. The slow rate of fire and fewer shells was balanced by devastating power, as the 122mm gun could penetrate a German Panther’s front armor at 2700 yards, and its side armor from 3800 yards.

That gave the Iosef Stalin tanks a significant standoff distance advantage versus the Panzer V Panthers. While an IS-2 could destroy a Panther from up to 3800 yards away, a Panther would have to close in to 870 yards to penetrate the IS-2’s turret, and 660 yards to penetrate its front armor. Against the Tiger, testing showed that the IS-2’s gun could penetrate its turret at 1600 yards, and its front armor from 660 yards.

The Iosef Stalin tank was even more effective against infantry, as its 122mm high explosive shells proved murderous against strong points and bunkers. At a pinch, the 122mm HE shells could also be fired at German tanks, and if they struck, no matter the distance, the explosion could cause cracking and even tear off the front armor’s weld.

The mechanical shock could disable the enemy tank even without penetrating its armor. Eventually, the very concept of heavy tanks was made obsolete by the introduction of main battle tanks. Nonetheless, IS tanks continued to serve around the world for decades after WWII, and were used as late as the Six Day War by both sides of the conflict.

Some Sources and Further Reading

Baryatinsky, Mikhail – The IS Tanks, IS-1, IS-2, IS-3 (2006)

History Halls – British Tanks of World War II: The Rugged Churchill

Stokes, Neil – KV Tanks on the Battlefield (2014)

Zaloga, Steven – IS-2 Heavy Tank, 1944-73 (2011)