Skysweeper

Skysweeper (Gun, M51, Antiaircraft or Gun automatic, 75-mm T83E6, and E7, recoil mechanism, and loader rammer) was an anti-aircraft gun deployed in the early 1950s by both the U.S. Army and U.S. Air Force. It was the first such gun to combine a gun laying radar, analog computer (director) and an autoloader on a single carriage.

The Skysweeper was introduced just as surface-to-air missiles were being deployed in the long-range role, replacing earlier anti-aircraft artillery systems. These missiles were very large and slow to react, which left short-range engagements to guns. The Army's existing guns were a motley collection of World War II-era systems that were barely effective then, and were considered largely useless against jet-powered aircraft. Missiles replaced all of the larger weapons, while Skysweeper replaced all the smaller ones.

The Skysweeper system was used for a relatively short period of time, from the mid to late 1950s in the US, and into the 1960s in some overseas locations. By that time newer missile systems were closing the range gap, and the Army was busy developing new weapons like the MIM-46 Mauler for this role. The last overseas Skysweeper were deactivated in the 1970s, never having been wholly replaced by other systems.

Anti-aircraft guns naturally fall into several categories, each for a different altitude and speed requirement. High-altitude targets require very large guns to get the needed power into the shell to reach those altitudes, but at the same time have the advantage of not needing to move very fast because at that range the change in angle of the target was small—consider the seemingly slow motion of an airliner at cruise altitude. At very low altitudes there were only seconds in which to react when spotting an aircraft over local terrain, so a hand-swung weapon was the only possibility, no matter how inaccurate. However, the short ranges meant that accuracy was not needed, nor was a large gun needed to cover the range.

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