Major General Richard Newton said: "Nothing like this has ever occurred."
"This was a failure to follow procedures, procedures that have proven to be sound."

According to Newton, a six-week investigation concluded that the transfer resulted from "a series of procedural breakdowns and human errors".

He said it was also "an erosion in adherence to weapons handling standards" at both air force bases.

"It was a lack of effective supervision, a lack of effective leadership, and the fact that they were not following, nor did they adhere to these very strict checklist guideline procedures."

Damage control 

Meanwhile, at least four officers were removed from their posts in the wake of the incident.

About 65 air force members also had their permission to handle nuclear weapons withdrawn.

The US military does not usually comment on the movement of nuclear arms but Michael Wynne, the secretary of the air force, said he had decided to make an exception.

Wynne said: "We would not be this upset with ourselves, nor be striving to restore confidence, if this did not involve nuclear weapons."

Attention to detail 

Air force members assigned at the bases' weapons storage area are said to have failed to examine all the pylons.

A pylon is a finlike device used to attach engines, fuel tanks or bombs to an aircraft wing or fuselage.

During an inspection, a pylon was moved to the aircraft by trailer, but air force personnel failed to verify that it had the right load.

"The crew is required to inspect the munitions before departing. They did not do that," Newton said.

The B-52 departed at 8.40am on August 30, arriving at Barksdale air base in Louisiana at 11.23 am.

It was not unloaded until about 8.30pm.

When the nuclear armed weapons were discovered,  Robert Gates, the US defence secretary and George Bush, the president, were notified.