History of WWII Willys Jeep
In 1940, the U S Army asked 135 tractor and car manufacturers to design and build a four-wheel drive, 40 horsepower, 1,300 pound reconnaissance car. The working prototype had to be available for a testing in 49 days. Only two companies responded, The American Bantam Car Company and Willys-Overland Motors. Because the Bantam Company promised to deliver the working prototype in 45 days, they won the contract.
The Army tested the prototype for 30 days. Unfortunately for Bantam, the War Department gave Ford and Willys the Bantam blueprints and they then each submitted prototypes to compete with the Bantam in the Army’s trials, the vehicles tested were the Willys Quad and the Ford Pygmy
Of the three prototypes the Ford looked more like the Jeep we know today. The initial contract was awarded in October, 1941. Jeeps supplied were the Bantam BRC 40, the Willys MA and the Ford GP.
Production of the standard jeep as we know it today started in 1942 with the Willys MB and the Ford GPW. Jeeps built by Willys up to April 1942 had slat grills, all Ford Jeeps had the distinctive stamped slotted grill, adopted by Willys from April 1942. 
The first 16,000 Willys MB’s and 15,000 Ford GPW’s bodies had the names Ford or Willys stamped in the rear panel, where on later Jeeps; the Jerry can would be placed. These are known as script Jeeps.
Until 1943 Willys and Ford used separately manufactured bodies. In early 1944 one manufacturer, the American Central Manufacturing Company began building bodies for both Ford and Willys. These bodies are referred to as “composite” bodies. The Bantam Car Company was not awarded a contract for any more Jeeps, but got the contract to build Jeep trailers. The engine was a 2,200cc side valve 4 cylinder, the Willys-Overland ‘Go Devil’ model. All engines were produced by Willys but in 1942 Ford began to produce GPW engines to the Willys design.
War time production of Jeeps was:
Bantam – Mk 11 / BRC 2,675
Willys – MA / MB 363,496
Ford – GP / GPW 281,448
Total 647,619
Ford also produced the GPA amphibious Jeep, known as ‘seeps’ some 12,778 were made.
The (French) Hotchkiss M201 Jeep was produced from 1955 to 1966 with some 27,628 being made.
Military Jeep Documentary
Willys Jeep the history