Complex sentence: The pilot vehicles used the M3 chassis with an open-topped superstructure, mounting an M1A2 105 mm howitzer and, following trials, adding a machine gun, the T32 was accepted for service as the M7 in February 1942 and production began that April.
Split into simpler sentences: The pilot vehicles used the M3 chassis with an open-topped superstructure, mounting an M1A2 105 mm howitzer, with a machine-gun added after trials. The T32 was accepted for service as the M7 in February 1942 and production began that April.