duction. There were roughly six versions of the tank based on the design and production modifications introduced.
The first variant was the baseline production IS-1 armed with the 85mm gun and three DT machineguns. For the sake of the hull's enhanced armor survivability and ease of production, some of these vehicles had their mid section (glacis) of their step bows slanted at a higher angle (75E compared to the previous 72E) as well as the length of the casting's sides reduced and the track adjuster's attachment to the hull side.
The second version had the same running gear as the IS-1, but a new turret had to be developed owing to the tank's D-25 screw-type breach lock gun with the German-type twin-chamber muzzle brake. It differed from the IS-1's turret in having the cupola and periscope sight's armored cover shifted to the left, bulged turret side on the left, gun's elongated armor protection cone and a hub on the mantlet.
Someone with an online name of Amizaur measured several JS-2s in Poland and did find that the cast armor of the step front JS-2 was 120mm of cast armor. In his examinations though he found that the castings varied by 5-10%. So the one captured by the Germans could be an early poorly made tank or transitional thickness.
[Research in the section is not complete]