U.S. Secretary of Defense Robert Gates (L) and Secretary of State Hillary Clinton smile during a joint news briefing on the new Nuclear Posture Review at the Pentagon in Washington April 6, 2010. The Obama administration, kicking off an intensive week of nuclear diplomacy, unveiled a revamped policy on Tuesday restricting U.S. use of its atomic weapons stockpile. REUTERS/Yuri Gripas (UNITED STATES - Tags: POLITICS MILITARY ENERGY)