M9 gun director

A US 90 mm anti-aircraft gun and crew during a demonstration at Bell Laboratories in 1943. The M9 gun director can be seen in the center background of the photo.

The M9 gun director was an electronic director developed by Bell Labs during World War II. This computer continuously calculated trigonometric firing solutions for anti-aircraft weapons against enemy aircraft. When cued by the SCR-584 centimetric gun-laying radar and used in concert with anti-aircraft guns firing shells with proximity fuzes, it helped form the most effective anti-aircraft weapon system utilized by the Allies during the war.