The Willys Jeep was designed and built with the sole purpose of mobilising the US army in the heat of World War II. The Overland Jeep revolutionised off-road driving for soldiers, and demand soon outstripped supply. Supply shortages meant Ford stepped in and built the Jeep under licence from Willys, adopting the instantly recognisable seven-slotted grille, which was much cheaper to produce than the original. After the war, Willys decided to offer the Jeep to civilians, and the CJ (Civilian Jeep) was born.
info from Octane