[1][2] Based on the M3 half-track chassis, it was produced by the Autocar Company between July 1942 and February 1944, and served alongside the M16 Multiple Gun Motor Carriage.

A 386-cubic inch (6.330 cc) White 160AX, 128-horsepower (95 kW), 6-cylinder gasoline engine gave the M15 a power-to-weight ratio of 15.8 horsepower per ton and a maximum road speed of 41.9 mph (67.4 km/h).

[8][9] A United States Army Armored Force requirement for a mobile anti-aircraft gun to support the coming North African Campaign resulted in the T28 project being revived soon after its cancellation.

[2] The new vehicles used the larger M3 half-track chassis and an M2E1 sight for target spotting,[10][11] receiving the designation T28E1 Combination Gun Motor Carriage (CGMC).

[12][13] A total of eighty T28E1s were produced from July to August 1942 by White,[2] all of which had a mount lacking protection for the gun combination and crew.

[20] The M15 "Special" was the unofficial name for an M15 (and probably other CGMCs) adapted in depots in Australia to carry only a single Bofors 40 mm gun.

[1][17][18] To enhance ground support firepower during the Korean War, depots in Japan were searched for vehicles that could be refurbished for possible combat use.

[20] The proficiency of this mobile weapon can be attributed to three characteristics: its mobility, enabling it to work well in close support of combat troops in forward areas and to patrol roads over which heavy traffic must travel under constant threat of bombing and strafing; its flexible firepower, combining the volume of caliber .50 with the knocking power of the 37 mm; and the facility which the fire is controlled, by using the tracer stream from the caliber .50 to bring it on target before opening up with the full volume of armament.

Numerous cases are cited in which a "mouse trap" effect has been obtained which enemy planes came in much closer on the initial caliber .50 fire than they would on a light cannon and were caught by the 37 mm.

[21] One T28E1 was captured at Kasserine by the Germans and rebuilt as an equipment and troop carrier to replace vehicles destroyed by Allied aircraft.

[22] Each US Army armored division was allocated an anti-aircraft artillery (AAA) battalion of four companies, each equipped with eight M15 CGMCs and eight M45 Quadmount-equipped M16 MGMCs.