Origin of the term "jeep"
There are many explanations of the origin of the word "jeep," all of which have proven difficult to verify. Probably the most popular notion holds that the vehicle bore the designation "GP" (for "Government Purposes" or "General Purpose"), which was phonetically slurred into the word jeep. However, R. Lee Ermey, on his television series Mail Call, disputes this, saying that the vehicle was designed for specific duties, was never referred to as "General Purpose," and that the name may have been derived from Ford's nomenclature referring to the vehicle as GP (G for government use, and P to designate its 80-inch (2,000mm) wheelbase). "GP" does appear in connection with the vehicle in the TM 9-803 manual, which describes the vehicle as a machine, and the vehicle is designated a "GP" in TM 9-2800, Standard Motor Vehicles, September 1, 1949, but whether the average jeep-driving GI would have been familiar with either of these manuals is open to debate.
This account may confuse the jeep with the nickname of another series of vehicles with the GP designation. The Electro-Motive Division of General Motors, a maker of railroad locomotives, introduced its "General Purpose" line in 1949, using the GP tag. These locomotives are commonly referred to as Geeps, pronounced the same way as "Jeep."
Many, including Ermey, suggest that soldiers at the time were so impressed with the new vehicles that they informally named it after Eugene the Jeep, a character in the Popeye cartoons that "could go anywhere."
The term "jeep" was first commonly used during World War I (1914–1918) by soldiers as slang for new recruits and for new unproven vehicles. This is according to a history of the vehicle for an issue of the U.S. Army magazine, Quartermaster Review, which was written by Maj. E. P. Hogan. He went on to say that "jeep" had these definitions as late as the start of World War II.
"Jeep" had been used as the name of a small tractor made by Minneapolis-Moline.
The term "jeep" would eventually be used as slang to refer to an airplane, a tractor used for hauling heavy equipment, and an autogyro. When the first models of the jeep came to Camp Holabird for tests, the vehicle did not have a name yet. Therefore the soldiers on the test project called it a jeep. Civilian engineers and test drivers who were at the camp during this time were not aware of the military slang term. They most likely were familiar with the character Eugene the Jeep and thought that Eugene was the origin of the name. The vehicle had many other nicknames at this time such as Peep (the term originally used in the Armored Force), Pygmy, and Blitz-Buggy, although because of the Eugene association, Jeep stuck in people's minds better than any other term.