David Gannon was born on July 2, 1947, in Centreville, Maryland. He enlisted in the U.S. Army on September 6, 1966, and was trained in the Field Artillery before entering Officer Candidate School on October 18, 1967. Gannon was commissioned a 2d Lt in the Field Artillery and then completed Helicopter Pilot Training, earning his wings as an Army Aviator on May 6, 1969. He then deployed to Southeast Asia, where he served with the 116th Assault Aviation Company of the 1st Aviation Brigade in the Republic of Vietnam from June 1969 to April 1970, followed by service as a Field Artillery Battery Commander at Fort Sill, Oklahoma, from April 1970 to November 1971. Capt Gannon then returned to Southeast Asia, this time flying with the 213th Assault Support Helicopter Company of the 1st Aviation Brigade from November 1971 to May 1972. Upon returning from his second tour in Vietnam, he left active duty and remained in the inactive reserves until November 1, 1973, when he joined the 97th Army Reserve Command at Fort Meade, Maryland. Maj Gannon served with the 195th Aviation Assault Support Company and the 327th Corps Aviation Company before retiring from the Army Reserve in 1985. After retiring from the Army, he worked as an Instructor and Chief Pilot with U.S. Air, flying the Shorts 330 and DHC-7 and -8.

His 2nd Distinguished Flying Cross Citation reads:

For heroism while participating in aerial flight evidenced by voluntary actions above and beyond the call of duty: Captain Gannon distinguished himself by exceptionally valorous actions while serving as aircraft commander aboard a cargo helicopter on a support mission to the 5th Vietnamese division forward elements who were in critical need of food and ammunition. On the first three missions supplies were provided and over 90 wounded were extracted. On the fourth missions mortar fire was received at the landing zone, however, the aircraft remained at the landing zone until all supplies were unloaded and the wounded placed on board. Captain Gannon returned to An-Loc for the fifth mission and again mortar rounds began falling and the aircraft sustained several hits causing structural damage, however, Captain Gannon expertly maneuvered the aircraft to a safe landing. Captain Gannon's actions were in keeping with the highest traditions of the military service and reflect great credit upon himself, his unit and the United States Army.