The US Army 2-1/2-ton series, 6×6 trucks were the most widely used tactical transport vehicle of World War II. Over 800,000 were produced, 562,750 by GMC alone. The first GMC 2-1/2-ton, 6×6 was basically a six-wheel drive commercial type, designated the ACKWX-353, which entered production in 1939. The French government ordered a sizable number of ACKWX-353s in 1939 which were diverted to the British when France fell to the Germans in 1940. In 1941, the militarized version of the 2-1/2-ton, 6×6 went into production. It was code named CCKW-353, which translated as follows: C= 1941; C= conventional cab; K= front wheel drive: W= tandem rear axle; 353= 164-inch wheelbase. Early production models featured a pressed-steel, civilian-style, rounded cab. As production progressed, the all-steel cab was replaced by a simplified cab, as displayed, with a canvas roof and side doors. The GMC “Jimmys” made up the bulk of the famous Red Ball Express which operated across Northern France during the fall of 1944. Several specialized versions of the CCKW series were produced; including gas and water tank trucks, dump trucks, mobile workshops, bomb service, prime movers and, as displayed, mobile air-compressors used by USMC engineering units.