The Pe-2 regiments' operations were not always successful and the service pilots complained about insufficient defensive armament and survivability: there was a great risk of fire and insufficient armour protection, especially for the navigators and gunners. German pilots soon discovered the limited sighting angles of the ventral gun mounting and its poor reliability. The ammunition belt of the UBT machine-gun often jammed after the first burst of fire when shooting in extreme positions. The navigator and the radio operator were poorly protected. On average, ten Pe-2 gunners were wounded for every pilot, and two or three were killed for the loss of one pilot.