seen in Croatia 2012
from wikipedia: Even though the world had seen wide-spread mechanisation of the military during World War I, and the US Army had already used 4x4 trucks in it, supplied by the Four Wheel Drive Auto Co. (FWD), by the time World War II was dawning, the United States Department of War were still seeking a light, cross-country reconnaissance vehicle.
As tensions were heightening around the world in the late 1930s, the U.S. Army asked American automobile manufacturers to tender suggestions to replace its existing, aging light motor vehicles, mostly motorcycles and sidecars but also some Ford Model T's. This resulted in several prototypes being presented to army officials, such as five Marmon-Herrington 4x4 Fords in 1937, and three Austin roadsters by American Bantam in 1938 (Fowler, 1993). However, the US Army's requirements were not formalized until July 11, 1940, when 135 U.S. automotive manufacturers were approached to submit a design conforming to the army's specifications for a vehicle the World War II technical manual TM 9-803 described as "... a general purpose, personnel, or cargo carrier especially adaptable for reconnaissance or command, and designated as 1/4-ton 4x4 Truck."
Marmon-Herrington converted Ford 1/2 ton truck, sometimes called the "Grandfather of the Jeep"
By now the war was underway in Europe, so the Army's need was urgent and demanding. Bids were to be received by July 22, a span of just eleven days. Manufacturers were given 49 days to submit their first prototype and 75 days for completion of 70 test vehicles. The Army's Ordnance Technical Committee specifications were equally demanding: the vehicle would be four-wheel drive, have a crew of three on a wheelbase of no more than 75 (later 80) inches and tracks no more than 47 inches, feature a fold-down windshield, 660 lb payload and be powered by an engine capable of 85 ft·lb (115 N·m) of torque. The most daunting demand, however, was an empty weight of no more than 1,300 lb (590 kg).
Only two companies entered: American Bantam Car Company and Willys-Overland Motors. Though Willys-Overland was the low bidder, Bantam received the bid, being the only company committing to deliver a pilot model in 49 days and production examples in 75. Under the leadership of designer Karl Probst, Bantam built their first prototype, dubbed the "Blitz Buggy" (and in retrospect "Old Number One"), and delivered it to the Army vehicle test center at Camp Holabird, Maryland on September 23, 1940. This presented Army officials with the first of what eventually evolved into the World War II U.S. Army Jeeps: the Willys MB and Ford GPW. Willys MA jeep at the Desert Training Center, Indio, CA, June 1942. The Ford car was then designated GPW, with the "W" referring to the "Willys" licensed design. During World War II, Willys produced 363,000 Jeeps and Ford some 280,000. Approximately 51,000 were exported to the U.S.S.R. under the Lend-Lease program. A further 13,000 (roughly) amphibian jeeps were built by Ford under the name GPA (nicknamed 'Seep' for Sea Jeep). Inspired by the larger DUKW, the vehicle was produced too quickly and proved to be too heavy, too unwieldy, and of insufficient freeboard. In spite of participating successfully in the Sicily landings (July 1943) most GPAs were routed to the U.S.S.R. under the Lend-Lease program. The Soviets were sufficiently pleased with its ability to cross rivers to develop their own version of it after the war (GAZ-46).