The issue of visibility was a known sore spot in early war Soviet tanks. The commander's cupola was not a popular feature until the T-50, but it took until 1942 for such a cupola to be developed for the KV-1 and T-34 tanks. The book Tank Observation Devices documents the improvement in observation range between the KV-1 and its successor, the KV-1S.
The dead zones of the KV-1 tank were as follows:
- Driver's large observation slit: 3.6 m
- Driver's small observation slit: 6.7 m
- Driver's periscope: 6 m
- Turret observation slits: 6.5 m
- Turret periscopes: 4 m
The dead zones of the KV-1S tank are as follows:
- Driver's large observation slit: 9 m
- Driver's small observation slit: 12 m
- Driver's periscope: 7.5 m
- Turret observation slits: 23 m
- Turret periscopes (front and rear): 17 m
- Commander's cupola: 28 m, 18 m, 14 m, 11 m, 9 m, depending on the observation device.