The 20mm Oerlikon, a manually operated anti-aircraft weapon, was mounted on a pedestal and could be trained through 360° and elevated from minus 5° to plus 87°. Aboard a US submarine, the 20mm was located on one or both of the submarine's gun platforms fore or aft of the periscope shears. Considered a close range, high angle  weapon, it was a recoiling, air cooled automatic AA gun which fired an explosive shell, including the "tracer" which glowed as it traveled towards its target and indicated the direction of fire. Manned generally by a three or four man crew it was capable of firing 450 rounds per minute, at 36° of elevation the 20mm AA gun had a maximum range of 5,500 yards