and that doesn't means this gun is not a effective anti-tank weapon, it's an answer to the German Panther and Tiger Tank, and it has proved itself of capable destroying both Tiger and Panther, and it's frontal armor is impenetrable for Tiger I & Panther at point blank range.
please google before you write down "Not an anti-tank role" I just don't want replying the ignorance ppl's naive comment anymore
Here are some quotes from the ever reliable wikipedia if you don't believe me about the role of this tank:
"German Army data on the penetration ranges of the 122 mm A-19 gun against the Panther tank showed it to be much less effective when the Panther stood at a side angle of 30 degrees to the incoming round: the A-19 gun was unable to penetrate the glacis plate of the Panther at any distance, and could only penetrate the bottom front plate of the hull at 100 m.[4] It was the large HE shell the gun fired which was its main asset, proving highly useful and destructive in the anti-personnel role. The size of its gun continued to plague the IS-2, and
the two-piece ammunition was difficult to handle and slow to reload (the rate of fire was only about two rounds per minute). Another limitation imposed by the size of its ammunition was the payload: only 28 rounds could be carried inside the tank."
From the section on the operation history of this tank:
"The IS-2 tank first saw combat in early 1944. IS-2s were assigned to separate heavy tank regiments, normally of 21 tanks each.[12] These regiments were used to reinforce the most important attack sectors during major offensive operations. Tactically, they were employed as breakthrough tanks.
Their role was to support infantry in the assault, using their large guns to destroy bunkers, buildings, dug-in crew-served weapons, and other 'soft' targets. They were also capable of taking on any German AFVs if required. Once a breakthrough was achieved, lighter, more mobile T-34s would take over the exploitation."
Bold added by me.