Women should be allowed to serve aboard America's fleet of nuclear submarines, the nation's top military officer, Adm. Michael Mullen, quietly has told the Senate Armed Services Committee. If the Navy agrees to it, this would be a huge policy change and potentially a significant expansion of career opportunities for female officers and sailors. Women have been barred by Navy policy from submarines, even as the sea service began 15 years ago to integrate females into other seagoing combat roles including aboard surface warships and in fighter jets. Mullen, former chief of naval operations and a career surface warfare officer,...