The Willys MB U.S. Army Jeep (formally the Truck, 1/4 ton, 4x4) and the Ford GPW were manufactured from 1941 to 1945. These small four-wheel drive utility vehicles are considered the iconic World War II Jeep, and inspired many similar light utility vehicles. The World War II Jeep later evolved into the "CJ" civilian Jeep.
Even though the world had seen widespread mechanisation of the military during World War I, and the United States Army had already used four-wheel drive 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.
One account of the origin of the term "jeep" begins when the prototypes were being proven at military bases. The term "jeep" was used by Army mechanics for any untried or untested vehicles.
Willys made its first 25,000 MB Jeeps with a welded flat iron "slat" radiator grille. It was Ford who first designed and implemented the now familiar and distinctive stamped, slotted steel grille into its cars, which was lighter, used fewer resources, and was less costly to produce. Along with many other design features innovated by Ford, this was adopted by Willys and implemented into the standard World War II Jeep by April 1942.
TEXT FROM WIKIPEDIA - WILLYS JEEP