Military slang is also used to reinforce the (usually friendly) interservice rivalries. Some of these terms have been considered derogatory to varying degrees and attempts were made to eliminate them. Those attempts have failed because many service members take a certain perverse pleasure in the sense of shared hardship which the nickname implies. Examples of slang terms for members of the various services include: ; Jarhead: A US Marine - a reference to the "high and tight" haircut ; G.I.: A US Army soldier - This phrase is often thought to come from "General Issue". The phrase actually comes from the initials for Galvanized Iron which were stamped on the trashcans during WWII. G.I. in verb form means to clean thoroughly as in to GI the barracks. ; Grunt: A US Army soldier - sometimes, but not always, specifically refers to an infantryman ; Dogface: A US Army infantryman - common in World War II ; Doughboy: Also a US Army soldier - this term is almost exclusively used in the context of World War I ; Gun bunny: A US Army artilleryman - often specifically a cannon crewman ; Squid: A US Navy sailor ; Throttle-jockey: A jet aircraft pilot, particularly one with a penchant for speed. ; Butterbar: A Second Lieutenant in the US Army, Air Force or Marines - a reference to the insignia of rank - a single gold bar. ; The Old Man: The unit commander ; Chair Force: the US Air Force, referring to the fact that a relatively small percentage of Air Force personnel ever see combat.