Defense Secretary Robert Gates retires (11 images)

Secretary of Defense Robert Gates, U.S. President Barack Obama and Chairman of the Joint Chiefs of Staff Adm. Michael Mullen participate in Secretary Gates' Armed Forces Farewell Ceremony on the Pentagon River Parade Field in Arlington, Virginia, on June 30, 2011. UPI/Roger L. Wollenberg

U.S. President Barack Obama (R), and Defense Secretary Robert Gates (L), watch a fife and drum corps during an Armed Forces Farewell Tribute in honor of Gates' departure at the Pentagon in Arlington, Virginia on June 30, 2011. Former CIA Director Leon E. Panetta will become the 23rd Secretary of Defense, replacing Gates on July 1. UPI/Jim Lo Scalzo/Pool

U.S. President Barack Obama awards Defense Secretary Robert Gates the Presidential Medal of Freedom during an Armed Forces Farewell Tribute in honor of Gates' departure at the Pentagon in Arlington, Virginia on June 30, 2011. Former CIA Director Leon E. Panetta will become the 23rd Secretary of Defense, replacing Gates on July 1. UPI/Jim Lo Scalzo/Pool

Secretary of Defense Robert Gates reviews the troops during an Armed Forces Farewell Ceremony in his honor on the Pentagon River Parade Field in Arlington, Virginia, on June 30, 2011. Former CIA Director Leon E. Panetta will become the 23rd Secretary of Defense, replacing Gates on July 1. UPI/Roger L. Wollenberg