Chairman of the Joint Chiefs of Staff Navy Adm. Mike Mullen visits a memorial on Camp Chapman, Afghanistan, July 31, 2011, commemorating seven CIA agents killed in a December 2009 suicide attack. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

From left: Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, speaks with comedian Jon Stewart, magician David Blaine and NBA legend Karl Malone in Kabul, Afghanistan, July 31, 2011. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, greets International Security Assistance Force soldiers assigned to Mehter Lam, Afghanistan, July 31, 2011. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

U.S. Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, and Lt. Gen. Sher Mohammad Karimi, chief of the General Staff of the Afghan National Army, depart the Ministry of Defense in Kabul, Afghanistan, July 31, 2011. Mullen is on a five-day USO tour with comedian Jon Stewart, NBA legend Karl Malone and magician David Blaine visiting troops in Afghanistan and Iraq. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

Navy Adm. Mike Mullen, right, chairman of the Joint Chiefs of Staff, walks with Marine Corps Gen. John R. Allen, center, commander of International Security Assistance Force, and Army Maj. Gen. Daniel B. Allyn, left, commander of ISAF Regional Command-East, after arriving at Bagram Air Base in Afghanistan, July 30, 2011. Mullen is on a five-day tour visiting troops in Afghanistan and Iraq. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, arrives at Bagram Air Base in Afghanistan, July 30, 2011. Mullen is on a five-day tour in Afghanistan and Iraq with USO celebrities, including comedian Jon Stewart, NBA Legend Karl Malone and magician David Blane. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

Chairman of the Joint Chiefs of Staff Navy Adm. Mike Mullen addresses Marines assigned to Forward Operating Base Jackson in Afghanistan, July 30, 2011. Mullen is on a five-day USO tour with comedian Jon Stewart, NBA Legend Karl Malone and magician David Blane visiting troops in Afghanistan and Iraq. DOD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley

Defense Secretary Leon E. Panetta talks with Navy Adm. James Winnefeld Jr., commander of North American Aerospace Defense and U.S. Northern Command, after arriving at Peterson Air Force Base, Colo., July 29, 2011. DOD photo by U.S. Air Force Tech. Sgt. Jacob N. Bailey