Homestead Air Force Base, Florida, in preparation for his first tour in Southeast Asia. Assigned to the 480th Tactical Fighter Squadron, 366th Tactical Fighter Wing at Da Nang Air Base, South Vietnam in 1968, Ritchie flew the first "Fast FAC" mission in the F-4 forward air controller program and was instrumental in the spread and success of the program. He completed 195 combat missions. In 1969, he was selected to attend the Fighter Weapons Course at Nellis Air Force Base, Nevada, becoming, up to that point, the Air Force Fighter Weapons School's youngest-ever instructor at age 26. He taught air-to-air tactics from 1970 to 1972 to the best USAF pilots, including Major Robert Lodge, who later became his flight leader in Thailand and himself shot down three MiGs. Ritchie volunteered for a second combat tour in 1972 and was assigned to the 432nd Tactical Reconnaissance Wing at Udorn Royal Thai Air Force Base, Thailand. Flying F-4 Phantom IIs with the famed 555th ("Triple Nickel") Tactical Fighter Squadron he shot down his first Mikoyan-Gurevich MiG-21 on 10 May 1972, scored a second victory on May 31, a third and fourth on July 8, and a fifth on August 28. All of the aircraft he shot down were MiG-21s, and all were shot down by the much-maligned AIM-7 Sparrow radar-guided air-to-air missile. Ritchie became the United States Air Force's first and only pilot ace of the Vietnam War. An advantage that the Triple Nickel pilots had over other US aircrews was that eight of their F-4D Phantoms had the top secret APX-80 electronic set installed, known by its code-name Combat Tree. Combat Tree could read the IFF signals of the transponders built into the MiGs so that North Vietnamese GCI radar could discriminate its aircraft from that of the Americans. Displayed on a scope in the WSO's cockpit, Combat Tree gave the Phantoms the ability to identify and locate MiGs when they were still beyond visual range. May 1972, kills 1 and 2 Ritchie's assignment on May 10, the first major day of air combat in Operation Linebacker, was as element leader (Oyster 3) of one of two flights of the F-4D MiGCap for the morning strike force. Oyster flight had three of its Phantoms equipped with Combat Tree IFF interrogators, and two days previously its flight lead, Major Robert Lodge, and his WSO Capt. Roger Locher had scored their third MiG