Donald H. Rumsfeld was sworn in as the 21st Secretary of Defense on January 20, 2001. Before assuming his present post, the former Navy pilot had also served as the 13th Secretary of Defense, White House Chief of Staff, US Ambassador to NATO, US Congressman and Chief Executive Officer of two Fortune 500 companies. Secretary Rumsfeld attended Princeton University on academic and NROTC scholarships (A.B., 1954) and served in the US Navy (1954-1957) as an aviator and flight instructor. In 1957, he transferred to the Ready Reserve and continued his Naval service in flying and administrative assignments as a drilling reservist until 1975. He transferred to the Standby Reserve when he became Secretary of Defense in 1975 and to the Retired Reserve with the rank of Captain in 1989. Full bio.