 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 . 
