In 1962, the Air Force commenced evaluation of the US Navy/US Marine Corps F-4 Phantom II as a possible replacement for older fighter aircraft in the counter-air, interdiction and close air support (CAS) roles. In January 1962, two Navy F4H-1 aircraft were loaned to USAF and, since the 18 September 1962 naming convention for all DoD aircraft had not yet taken effect, were given the interim designation of F-110A Spectre. Twenty-four additional USN F4H-1 aircraft, subsequently redesignated as F-4Bs, were loaned to USAF for additional evaluation. This evaluation resulted in a USAF decision to acquire their own version of the F-4, designated as the F-4C. Following its initial flight in May 1963, the F-4C entered USAF service with TAC in November 1963. The F-4 would prove to be one of the most numerous jet fighters ever operated by USAF, with over 2800 examples acquired for service in TAC, USAFE, PACAF and the Air Force Systems Command (AFSC), to include later versions such as the RF-4C, F-4D, F-4E and F-4G.