McDonnell Douglas F-4C Phantom II, USAF Users, part one

Initially the F-4C in the United States Air Force, was going to be called F-110 Spectre, before the introduction of the 1962 Tri-Service designation system. As the aircraft proved to be a very nice one, they quickly adopted it and became it's largest user.

The first Phantoms to serve in Vietnam with the USAF were the F-4Cs from the 555th Tactical Fighter Squadron, that arrived in December 1964. Differing from the navy and marine counterparts where a naval aviator sat in the front place and a naval flight officer in the back, acting as an interceptor officer, the USAF's ones employed two pilots on each Phantom, on both seats. The one in the back could also pilot the airplane, albeit having less flying instruments and worse visibility. Later it was decided that a qualified Air Force Navigator acting as a weapons/targeting systems officer in the rear, instead of another pilot. However, every Phantom serving with the USAF retained their dual controls.

Sources:
1. https://en.wikipedia.org/wiki/McDonnell_Douglas_F-4_Phantom_II#United_States_Air_Force
2. Salamander Books - The Complete Book of Fighters