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M1 40mm Bofors Anti-Aircraft Artillery
The most significant light antiaircraft gun of World War II was the 40mm gun made by made by Bofors, a Swedish manufacturer. The design was developed in Sweden during the 1930s and was adopted for American military use, first by the Navy in 1938 and by the Army in 1941. Production was initially small and most guns were delivered to the Navy, but by early 1943 the 40mm Bofors reached Army antiaircraft units in quantity.
The 40mm Bofors Anti-Aircraft Artillery fired a two pound projectile that exploded on contact. The ammunition was packed in clips of four rounds that fed via a chute on the top of the gun. The rapid-firing gun could operate up to 120 rounds per minute in bursts, faster than they could be fed by the crew. The gun was mounted on a four-wheel trailer -- similar to that of the M1A2 37mm antiaircraft gun -- that was towed behind a light truck at road speeds. The platform allowed the gun a 360° traverse and outriggers were provided to stabilize the platform for firing. No shield for the crew was provided.
40mm Bofors Antiaircraft Gun Gun Sights and Directors
The 40mm Bofors Antiaircraf gun crews had several methods to sight the weapon on a target. Each gun platoon (four guns) had an M5 Director, connected by cables to the guns and all fed by a common generator. In this configuration, the platoon could engage a single target simultaneously. However, in combat the crews preferred to use the Bofors speed-ring sights. The crew of each weapon had an azimuth and elevation tracker seated in bucket seats on each side of the weapon. The elevation tracker had a foot pedal to fire the gun when the sight picture was right. Each 40mm round had a tracer element to aid in correcting the lead when the first rounds missed. Later in the war, the M-5 Director was replaced by the M-7 Computing Sight ("Weissight"), an "on-carriage" aiming device mounted on the gun with tracking telescopes for the azimuth and elevation trackers. The M7 Computing Sight eliminated the need for a separate director section, its director, generator, cables, and centralized control.
In early 1943 experience in the North African Theater showed that the 40mm guns had trouble keeping up with the units they supported. As soon as the AAA units got their M5 Directors emplaced and aligned, they were alerted to move. To correct this problem, the British "Stiff Key Stick," on-board fire control device for the Bofors developed by the British was adopted.
Organization of the 40mm Bofors Antiaircraft Gun Battery
Each automatic weapons battery had two gun platoons. Each platoon had four 40mm guns (and four Quad-50 machine guns on tracks or trailers). The platoons could mass their fire, or engage several targets simultaneously.