KANDAHAR, AFGHANISTAN - JUNE 05:  U.S. Secretary of Defense Robert Gates (R) hands a challenge coin bearing his name to a soldier as he thanks troops for their service at Forward Operating Base (FOB) Walton June 5, 2011 in Kandahar province, Afghanistan. The gradual withdrawal of U.S. combat troops from Afghanistan set to begin next month will be done responsibly and will not expose other coalition and Afghan forces to undue risks, Gates said on Sunday.  Gates arrived on his final trip to Afghanistan as Pentagon chief, following his address to the 10th IISS Asia Securities Summit in Singapore.  (Photo by Jason Reed - Pool/Getty Images)