Russian JS-1/JS-85 Armor Corrected

The JS-1/JS-85 was further development of the Soviet heavy tank program.   It may or may not have used the same turret as the KV-85.   An official looking armor scheme is shown at the right.  While the hull is clearly different the turret is the same design of the KV-85.  But since we don't have photos of captured JS-85s the actual values are in question. 
In the beginning of July 1943 two versions of the JS tank were ready for testing.  One with a S-31 85mm gun and one with the D5-T 85mm gun (Object #237).   At the same time two tanks built on the KV-1S chassis were also ready.  One had the modified KV-1S turret with an S-31 gun (Object #238) and the other (Object #239) had a turret from Object #237.  In the tests the winners were Object #237 and Object #239.   These were renamed JS-85 and KV-85 respectively.

Development history link
In the early blueprint in this article link counting pixels the thickness as correct the front drivers plate of 120mm@30° will give the glacis of 62-74mm @75° and lower front plate of 100mm@30° . 

To the right are photos of captured JS-2 with the step front.  The thickness values differ from the drawing armor scheme. The front hull of 120mm drawing is 105mm when the tank is built.  The lower hull is only 95mm when the drawing says it should be 100mm. The turret rear is shown in the drawing is 100mm but the Germans found it to be 110mm.  Also, along the side are some applique armor panels that increase the armor from 90mm to 95mm. 

We have seen from the previous page that the armor of the turret of the KV-85 is different than the final JS-2.  Did the Russians change the armor thickness of the JS series before or after the 122mm gun was installed?   The following may answer that question.

The IS tank's configuration changed considerably during pro

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]