Mustang is a military slang term used in the United States Armed Forces to refer to a commissioned officer who began their career as an enlisted service member.
Department of Defense military pay tables authorize approximately ten percent pay premiums for officers in grades O-1, O-2 and O-3 who have credit for over four years of enlisted or warrant officer service before commissioning (Grades O-1E, O-2E, O-3E).
[2] A mustang is characterized by former enlisted service before transitioning to officer rank.
As a slang term, there is no official U.S. Government definition or set of criteria to determine which officers can properly be called a mustang.
By the end of World War II, it was understood across the armed forces that a Mustang was an officer with service in the enlisted ranks before commissioning.