There have been 225 four-star generals in the history of the U.S. Air Force. Of these, 221 achieved that rank while on active duty, 3 were promoted after retirement, and one was promoted posthumously. Generals entered the Air Force via several paths: 60 were commissioned via the U.S. Military Academy (USMA), 49 via the aviation cadet program, 44 via the U.S. Air Force Academy (USAFA), 40 via Air Force Reserve Officer Training Corps (AFROTC) at a civilian university, 12 via AFROTC at a senior military college, 8 via Air Force Officer Training School (OTS), 4 via the U.S. Naval Academy (USNA), 4 via Reserve Officer Training Corps (ROTC) at a civilian university, 2 via direct commission (direct), one via direct commission inter-service transfer from the Army National Guard (ARNG), and one via direct commission inter-service transfer from the Royal Canadian Air Force (RCAF).