Advances in both guns and radar fire control toward the end of World War II, coupled with higher speed aircraft, led the Army to seek a more powerful medium range/medium caliber anti-aircraft weapon. Building on technology used in the Navy’s 3”/50 automatic anti-aircraft gun, the Army developed a high velocity 75mm automatic gun fed from a 10 round magazine. Coupled with a lightweight radar and a gunfire director, the result was the M51 Skysweeper.
For the first time, the Army had mounted the gun system, the director, and the fire control radar on one carriage .
Designed to counter low and medium altitude threats up to 700 miles per hour, the M51 was developed in the early 1950s, and eventually deployed to complement 90mm and 120mm anti-aircraft guns deployed by the Army’s Anti-Aircraft Artillery Command to defend major US cities.
Even rapid fire radar directed guns struggled to successfully engage fast flying jets, and were overtaken by surface-to-air missile systems such as the Nike Ajax, which was widely fielded throughout the country. By 1957, the Skysweeper had been relegated to strictly second line duties, though examples soldiered on until as late as the 1970s.