The US Army realized that with the coming war in Europe, mobile artillery was a must and self-propelled artillery was ideal. Early adaptations of half-track-based gun mounts revealed that the best system would have to be armored and fully tracked. The first iteration of a fully tracked and armored carriage was the pairing of a 105mm howitzer with a reworked M3 Lee chassis. This pairing was designated as the T32 during its development and trials, and upon production authorization was redesignated at the M7 Howitzer Motor Carriage.

During early production of the M7, a number of these vehicles were diverted to support the British A