** FILE ** Defense Secretary Leon E. Panetta (center right) walks across the apron with Army Gen. Lloyd J. Austin III (center left), commander of U.S. forces in Iraq, after arriving in Baghdad on Thursday, Dec. 15, 2011. Mr. Panetta was participating in ceremonies marking the end of the U.S. military mission in Iraq. (AP Photo/Pablo Martinez Monsivais, Pool)

Photo by: Pablo Martinez Monsivais

** FILE ** Defense Secretary Leon E. Panetta (center right) walks across the apron with Army Gen. Lloyd J. Austin III (center left), commander of U.S. forces in Iraq, after arriving in Baghdad on Thursday, Dec. 15, 2011. Mr. Panetta was participating in ceremonies marking the end of the U.S. military mission in Iraq. (AP Photo/Pablo Martinez Monsivais, Pool)