IS-1

by Thorleif Olsson

When more firepower was needed, the old KV-1 was fitted with an 85mm L/53 gun. This design was called IS-1 or IS-85. The later IS series was named after Iosef Stalin himself. The IS-1 was never to be produced in large quantity, and production ceased in 1944. The IS-1 was a very important design for the tank development in the future, and its later replacement, the IS-2 and IS-3 became the world leading tanks in the immediate post-war years. The IS-1 owed much to the old KV design, but had a modified hull, improved suspension and transmission. It was heavily armoured and had a new turret, mounting the same gun as on the T-34/85, SU-100 or later IS-2.

The need for greater firepower led to trials with a 100mm gun and a 122mm gun, where the 100mm gun proved superior. Nevertheless, the 100mm gun was just a little bit better than the 122mm gun and there was spare capacity to produce 122mm guns. The new vehicles were now fitted with either a 100mm L/60 gun (IS-100) or 122mm L/43 gun (IS-122) and later, these vehicles were given IS-2 standards. In November 1943, IS-100 and IS-122 tanks were put through firing trials at NIIBT in Kubinka. A captured Panther tank was used as training target and a 122mm round crashed through the frontal armor and clear through the rear armor as well. However, the 100mm gun had better armor penetration. A surplus of 122mm tube production facilities resulted in that the new 122mm gun was now chosen as the main armament to future tanks.

Some IS-1 saw service in Ukraine in early -44, operating as a heavy breakthrough tank, but most of them were used up in the Soviet winter campaigns of 1943/44.

IS-1

(Courtesy of Thorleif Olsson)