President Obama on Friday announced former Pentagon official Ashton Carter as his choice to lead the Defense Department, calling him one of America's top national security leaders who has a "relentless dedication to our armed services." The president's selection of Carter, 60, who was deputy defense secretary from October 2011 to December 2013, was widely rumored but not confirmed by the White House until now. If confirmed by the Senate, Carter would be Obama's fourth Pentagon chief in his roughly six-year administration.