Defense Secretary Robert M. Gates has nominated Gen. Martin E. Dempsey to succeed Gen. George W. Casey Jr. as Army chief of staff. Dempsey, 58, is now commander of the Fort Monroe, Va.-based Training and Doctrine Command, and served previous tours in Iraq as commander of the 1st Armored Division and the Multinational Security Transition Command. He also served as acting commander of U.S. Central Command. He graduated from the U.S. Military Academy at West Point, N.Y. Casey, who has served as chief of staff since 2007, will retire.