The immediate reason for the requested resignations of General Michael Moseley, the Air Force chief of staff, and Air Force Secretary Michael Wynne was a report on the accidental shipment of nuclear triggers to Taiwan.

The nuclear-trigger investigation - led by Admiral Kirkland Donald, the military's senior official on nuclear safety matters - found that the Air Force was failing to focus on its nuclear mission even after a high-profile incident last year in which a B-52 bomber crew unknowingly flew six nuclear warheads from North Dakota to Louisiana.

'The stewardship of our nuclear deterrent is the most sensitive mission that we have,' Mr Gates told a Pentagon news conference on Thursday. 'The declining standards...in my view required strong action.'

The Defence Secretary was particularly disappointed that the Air Force had not taken significant steps to shore up its nuclear controls after the B-52 incident, said Pentagon press secretary Geoff Morrell.

The nuclear weapons, on cruise missiles attached to the plane's wings, were not discovered missing from their repository at Minot Air Force Base for about 36 hours.

Mr Gates said the dismissals were necessary because the Air Force began focusing on its nuclear problems only after the shipment to Taiwan was disclosed earlier this year.

He acknowledged that problems in securing the United States' nuclear arsenal go back decades, but added that the current leadership should have recognised and corrected them.

Mr Gates said the two dismissals were based solely on Adm Donald's classified report, which he received last week. Officials briefed on the findings said it was highly critical of Air Force handling of nuclear technology.

The parts shipped to Taiwan included four electrical fuses used to trigger nuclear weapons aboard US missiles. The fuses were shipped to Taiwan by the Defence Logistics Agency, but the Air Force provided the fuses.

The fuses were sent to Taiwan in 2006 and the mistake went undetected until March this year.

Defence policy analyst Loren Thompson at the Lexington Institute said that apart from the 'formal reason' for the dismissals, Mr Gates felt that 'the Air Force just wasn't on the policy page he was on'.

On Capitol Hill, Democrats praised Mr Gates' quick action and for holding senior officials accountable for failures, unlike his predecessor Donald Rumsfeld.

Mr Gates appointed former defence secretary James Schlesinger to head a task force to ensure the 'highest levels' of control over nuclear weapons.

He already has candidates in mind to replace Mr Wynne, and possible replacements for Gen Moseley include General Kevin Chilton, head of US Strategic Command; General John Corley, chief of Air Combat Command; and General Norton Schwartz, head of US Transportation Command, according to defence officials.

LOS ANGELES TIMES, WASHINGTON POST