Bob Gregory was born on March 22, 1932, in Cape Girardeau, Missouri. He enlisted in the Missouri Army National Guard on March 17, 1949, and served until being selected for the Aviation Cadet Program and going on active duty with the U.S. Air Force on January 27, 1954. He was commissioned a 2d Lt and awarded his pilot wings at Greenville AFB, Mississippi, on April 29, 1955, and then attended F-86D Sabre Interceptor training at Perrin AFB, Texas, from May to September 1955. Lt Gregory next served as an F-86D pilot with the 318th Fighter Interceptor Squadron at McChord AFB, Washington, from September 1955 to October 1956, followed by service as an F-86D pilot with the 512th Fighter Interceptor Squadron at RAF Bentwaters, England, and then at Ramstein AB, West Germany, from November 1956 to June 1959. Capt Gregory served as an F-86D pilot with the 7127th Support Group and the 38th Air Base Group at Sembach AB, West Germany, from June to September 1959, and then attended Instructor Pilot Training at Moody AFB, Georgia, from October 1959 to February 1960. His next assignment was as an instructor pilot with the 3552nd Flying Training Squadron at Moody AFB from February to October 1960, followed by service as an instructor pilot with the 3575th Pilot Training Squadron at Vance AFB, Oklahoma, from October 1960 to September 1965. He attended RF-4C Phantom II Combat Crew Training and Reconnaissance training at Shaw AFB, South Carolina, from September to December 1965, and then served as an RF-4C pilot with the 9th Tactical Reconnaissance Squadron at Shaw from December 1965 until he deployed to Southeast Asia in July 1966. Capt Gregory served as an RF-4C pilot with the 6461st Tactical Reconnaissance Squadron at Udorn Royal Thai AFB, Thailand, from July to November 1966, and then with the 11th Tactical Reconnaissance Squadron at Udorn from November 1966 until he was forced to eject over North Vietnam and was taken as a Prisoner of War on December 2, 1966. It is believed that at some point after his capture he died in captivity, but the exact date of his death is unknown. He was listed in a Prisoner of War status and promoted through the ranks to Lieutenant Colonel before being declared dead on November 19, 1973. Lt Col Gregory's remains were returned to the United States on March 2, 1988, and he was buried at the Cape County Memorial Park Cemetery in Cape Girardeau, Missouri.

His Silver Star Citation reads:

Captain Robert R. Gregory distinguished himself by gallantry in connection with military operations against an opposing armed force near Hanoi, North Vietnam on 23 November 1966. On that date, Captain Gregory, despite extremely hazardous conditions, reconnoitered the Dap Cau Railroad and Highway Bridge near Hanoi. This night, low level mission imposed great demands upon the resources and capabilities of the pilot. Exposing himself for fifty-five minutes over hostile territory in a highly sophisticated and lethal anti-aircraft defense structure, Captain Gregory displayed outstanding determination in successfully obtaining the required intelligence on their assigned target. This intelligence was instrumental in restricting the flow of vital materials transported on the railroad leading northwest from Hanoi to Communist China. By his gallantry and devotion to duty, Captain Gregory has reflected great credit upon himself and the United States Air Force.