Development of the SPG started in the second half of 1941. The prototype underwent trials on February 12, 1942 and saw service in July 1942. The Pressed Steel Car Company produced 100 vehicles. Baldwin Locomotive Works modified the SPGs and re-equipped some M30 carriers. The vehicle saw service in the field artillery battalions and was used by the U.S.A. forces in Western Europe.
Time for the successive autoreloading of each shell into the magazine.
Characteristics are specified for Siege mode.
Characteristics are specified for Rapid mode.
Reload time of the first and second guns on double-barreled vehicles.
Characteristics are specified for vehicles with crews trained to 100%.