15. The Red Army’s Heavy Tank
In 1941, Germany’s dedicated armor-killing tank, the Panzer III, had a 37mm gun whose shells simply bounced off the Soviet heavy KV tanks. The Germans quickly upped their firepower, upgraded their Panzer IVs with more powerful antitank guns, and in 1942, rushed the Panzer VI Tigers into service with powerful 88mm guns. Against the Tigers’ thick armor, especially up front, the KV’s 76.2mm gun proved largely ineffective. Moreover, the slow KVs were unable to maneuver and close in quickly, like lighter T-34s could, to fire at the Tigers from closer ranges and at weaker spots so as to inflict damage. With a weak gun that could not damage the German heavy tanks, and armor that could be penetrated by the Tigers from long range, 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.
So the Soviets upped their heavy tank game with the Iosef Stalin (IS) line, developed to replace the KV heavy tank family and address its shortcomings. The IS proved a success during the war and went on to set the template for Soviet tanks for decades. 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. IS tanks had thicker armor than the KV, but because of a better layout 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.