In 1939, the army was in need of something new. Frustrated with the antiquated motorcycle and sidecar, and looking to replace the Model T Ford, which was (astonishingly) still in use for combat situations, the Army put out a call to auto manufacturers to develop a new brand of durable, rigorous, fast, light, and strong cars for use in combat, hauling, personnel movement, and a great deal of other applications.
There was a list of requirements, the most important of which were the gross vehicle weight (1200 lbs.), hauling capability (600 lbs.), four wheel drive, speed capabilities of at least 50 mph, and a rectangular-shaped body. Three automobile manufacturers entered the bidding (out of 135 invitations), with the Willys-Overland companys prototype (left) winning out over Bantam and Ford after rigorous testing which included fully loaded Jeeps run through a wide variety of troublesome terrain. In fact, in order to achieve the durability the Army desired, the army instructed their test drivers to break the cars if possible.
However, as America got involved in the war, it became evident that the Willys-Overland company was not able to produce the necessary amounts of Jeeps needed; the company simply did not have the necessary infrastructure. However, Ford did. In a unique request, the Army asked ford to produce the Willys-Overland design, so as to make all parts interchangeable.
Ford produced the GPW model, while Willys-Overland produced the MB model. Keep in mind that these two vehicles were largely the same.
Fords GPW Model. 277, 896 built by wars end
Willys-Overland MB model. 335,531 units produced by wars end
With Fords assistance, the Jeep became one of the most important pieces of machinery in the war. It was used to build bridges, haul ammunition and troops, clear roads, provide impromptu altars, be an ambulance, provide battlefield support with mounted machine guns, and of course, just be a car.
The Axis powers tried to create their own version of the Jeep. The Nazis produced the Volkswagen, which did not stand up to battlefield rigor. The Japanese made the Datsun, which like the Volkswagen, was ineffective in battle.
However, upon liberating much of Central Europe, the GIs who had become so attached to their beloved Jeeps were in for a big surprise. As they descended upon Germany in their Ford-made trucks, they quickly saw that the Nazis were also driving Ford-made automobiles. In fact, the relationship between Ford and Nazism was well-established well before the war. Hitler admired the assembly line technology, developed by Ford, so much that he kept a picture of Henry Ford on his desk. In fact, the German leader bestowed the highest honor possible upon a foreigner upon Ford in 1938, the Grand Cross of the German Eagle. A month later, James Mooney, a senior executive for GM, accepted an award for distinguished service to the Reich. As Michael Dobbs states in the Washington Post, Nazi Armaments chief Albert Speer told [author Bradford Snell] in 1977 that Hitler would never have considered invading Poland without synthetic fuel technology provided by General Motors.
Regardless, the Jeep was so rugged, trustworthy, and technologically superior to any other car that it was not replaced until the development of the HUMVEE in 1981. Civilian models of advancements on the original Jeep are still in production today, thanks to Allied World War Two innovations.
(Willys-Overland prototype image taken from http://www.willysoverland.com/history.html)
 Pictures, statistics from: Redmond, Derek. The Universal Jeep 1942-1986, A Timeline http://www.film.queensu.ca/CJ3B/Poster/GPW.html
 Dobbs, Michael. Ford and GM Scrutinized for Alleged Nazi Collaboration The Washington Post November 30, 1998 http://www.washingtonpost.com/wp-srv/national/daily/nov98/nazicars30.htm