85 mm Guns

Rival D-5 and S-31 guns might appear identical to the casual observer, but in reality, they had many subtle differences. The following data sheet contains the some data values regarding the KV-85 and IS-1 tanks that reveals some of them.

	IS tank, S-31 gun	IS tank, D-5 gun	KV-1S tank, S-31	KV-1S tank, D-5
Tank length	8460	8420	8210	8450
Tank width	3060	3060	3270	3270
Height (gun horizontal)	2700	2700	2600	2600
Height (gun elevated)	3280	3160	2600	3365
Clearance	380	380	380	400
Width between tracks	3060	3060	3265	3265
Track in contact with ground, length	4540	4700	4600	4600
Track in contact with ground, width	650	650	650	650
Vertical gun angle	-2 to +21	-3.5 to +22	-3.5 to 15	-2.75 to 23
Horizontal gun angle	360	360	360	360
Bore axis height	1900	1945	2070	1965
Gun dead zone (m)	50	23	42	35
Shell mass	AP: 9.2 kg HE: 9.54 kg
Total round mass	AP: 15.85 kg HE: 16.2 kg
AP muzzle velocity	800	800	800	800
Muzzle energy (ton-meters)	300	300	300	300
Penetration at 1000 meters at a 30 degree angle	83-98 mm

CAMD RF 38-11355-1529

As we can see, there are some differences in the size of the tanks that accommodate the gun, as well as various features, most notably gun depression. The IS can depress the D-5 more than the S-31, and even though the KV-85 can depress the S-31 slightly more, the higher bore axis gives that gun a much larger dead zone. Additionally, 15 degrees of gun elevation is quite unacceptable for a breakthrough tank that is expected to fight in urban conditions.