Had extra 25-35 mm of armor that was screwed onto the turret and welded to bow and driver's area. Starting in 1942 these had a cast turret. A hull machine gun was added.
Some of the KV-1s had extra armor added. Some had apliqué armor added, while others had screens attached by bolts.
The foundries at Kuznets Basin produced a cast turret. This turret weight over seven tons.
In 1941 the 76.2 mm ZiS-5 was first installed in the KV-1.