M51 “Skysweeper” anti-aircraft guns on display at Lewis Army Museum, Joint Base Lewis-McChord. The M51 was the first anti-aircraft weapon to combine a gun laying radar, firing computer, and autoloader on a single carriage. The Skysweeper was armed with the T83E1 (later M35) 75 mm anti-aircraft gun equipped with two 10-round autoloader magazines. The 75 mm rounds had a maximum range of 13.5 km and an effective range of 6.3 km. Skysweepers were used in the US from the early to mid 1950s, and in overseas locations from the 1950s to the late ‘60s and early ‘70s.