After a brief enlistment in the United States Marine Corps Reserve, General Clapper transferred to the Air Force Reserve Officer Training Corps program. He was commissioned in 1963 as a distinguished military graduate from the University of Maryland. He commanded a signals intelligence detachment in Thailand (where he flew 73 combat support missions in EC-47s), a signals intelligence SIGINT wing at Fort George G. Meade, Maryland, and the Air Force Technical Applications Center, Patrick Air Force Base, Florida. Clapper served as director of intelligence for three of the unified commands: U.S. Forces Korea, U.S. Pacific Command and Strategic Air Command. Also, he served as senior intelligence officer for the Air Force.[3] Clapper's final military post was as Director of the Defense Intelligence Agency. After this he briefly served as an executive in several private companies such as Booz Allen Hamilton and SRA International.
[edit] Appointment as USD(I)

After his departure from NGA in June 2006, Clapper briefly served as the chief operating officer for Detica DFI, now a US-based subsidiary of BAE Systems. For the 2006-2007 academic year, Clapper held the position of Georgetown University’s Intelligence and National Security Alliance Distinguished Professor in the Practice of Intelligence.[4] While teaching at Georgetown, Clapper was officially nominated by President George W. Bush to be Under Secretary of Defense for Intelligence on 29 January, 2007. Clapper was confirmed by the United States Senate on 11 April 2007.[5] He was only the second person to hold this position, which oversees and provides policy, program, and budgetary guidance to the defense intelligence agencies - DIA, NGA, the National Security Agency (NSA), and the National Reconnaissance Office (NRO) - and also works closely with the Director of National Intelligence (DNI).