The British and American armies wanted a half track that would carry an anti tank gun. An M3 half track was adapted in 1941 by adding M1897A 75 mm gun.
The M3 75 mm Gun Motor Carriage had the fuel tanks moved towards the rear to make room for the 75 mm gun.
The 75 mm M1897A was a copy of a French gun used in World War I.
Initially the gun shield was the full height version, but this caused the silhouette to be too high, so it was reduced.
Gun would fire at velocity of 2,000 ft/sec and penetrate 3 inches at 1,000 yards. Detachable canvas top. The APC shell weighed 18 lbs.