Audit is ordered for U.S. nuclear arsenal

Gates had already ordered a high-level investigation into how the four nose-cone fuse assemblies for U.S. intercontinental ballistic missiles were shipped overseas in place of common helicopter batteries -- the military's second major nuclear-related incident in less than a year.

Senior Pentagon officials have called the episode "extremely embarrassing," and it has both strained relations with China and called into question the U.S. military's ability to maintain its arsenal of catastrophic weapons.

"This is about the trust and confidence of the American people and our stewardship of the most dangerous weapons in the world," said Geoff Morrell, the Pentagon's press secretary.

"Getting to the bottom of this incident and ensuring our nuclear arsenal and associated components are properly safeguarded must be a top priority of this department. Secretary Gates believes this situation is totally and completely unacceptable."

Gates has ordered the Air Force, the Navy and the Defense Logistics Agency to take inventory of and assess control measures for all nuclear weapons and their associated parts within 60 days "to verify positive control and accountability of all such materials," according to a memo released Thursday.

Though the United States has tight control procedures for such devices and equipment, those measures did not prevent the nose cones from being shipped overseas without anyone noticing.

The measures also failed last August, when the Air Force unknowingly flew nuclear warheads between North Dakota and Louisiana, losing track of them for 36 hours.