 In USAF service, the F-4 was initially designated the F-110 Spectre prior to the introduction of the 1962 United States Tri-Service aircraft designation system. The USAF quickly embraced the design and became the largest Phantom user. The first USAF Phantoms in Vietnam were F-4Cs from the 555th Tactical Fighter Squadron "Triple Nickel", which arrived in December 1964.
