The M19 evolved from the 40 mm Gun Motor Carriage T65 project, which was based on an Armored Force requirement for a light anti-aircraft vehicle based on the M5 light tank chassis.
The T65E1 was accepted into service as the M19 Gun Motor Carriage in May 1944 with an order for 904 production models,[REF][REF] which was sent to Cadillac [REF].