90 Mm Gun M1/M2/M3 - Anti-aircraft Operation

Anti-aircraft Operation

In anti-aircraft use the guns were normally operated in groups of four, directed by the M7 or M9 Director or Kerrison Predictors. Radar direction was common, starting with the SCR-268 in 1941, which was not accurate enough to directly lay the guns, but provided accurate ranging throughout the engagement. For night-time use, a searchlight was slaved to the radar with a beam width set so that the target would be somewhere in the beam when it was turned on, at which point the engagement continued as in the day. In 1944 the system was dramatically upgraded with the addition of the SCR-584 microwave radar, which was accurate to about 0.06 degrees (1 mil) and provided automatic tracking as well. With the SCR-584, direction and range information was sent directly to the Bell Labs M3 Gun Data Computer, and M9 Director, which could direct and lay the guns automatically. All the operators had to do was load the guns. With the SCR-584 the 90 mm became arguably the best anti-aircraft weapon of the war.