WASHINGTON, Oct 20: The Pentagon has acknowledged that US Air Force officers failed on five occasions when they allowed a B-52 bomber to load nukes and fly across the country on Aug 30.

The incident caused US Secretary of Defence Robert M. Gates to order a review of the Pentagon’s handling of nuclear weapons.

A Pentagon investigation report, presented to Secretary Gates on Friday, said there were at least five occasions when air force weapons officers could have prevented the loading of six nuclear-armed cruise missiles on the plane.

The crew, unaware that they had nuclear cargo aboard, took off from the Minot Air Force Base in North Dakota and flew for nearly three hours, landing across the country at Barksdale Air Force Base in Louisiana.

The Pentagon investigation, however, showed that the nuclear weapons sat on a plane on the runaway at Minot Air Force Base for nearly 24 hours without ground crews noticing that the warheads had been moved out of a secured shelter.

This is the first known incident since the dawn of the atomic age in which the military lost track of its nuclear weapons for 27 hours. “This was an unacceptable mistake,” said Air Force Secretary Michael W. Wynne at a Pentagon news conference. “We would really like to ensure it never happens again.”

According to the Pentagon report, on Aug 29, North Dakota crew members were supposed to load 12 unarmed cruise missiles in two bundles under the B-52’s wings to be taken to Louisiana to be decommissioned. But in what the Air Force has ruled were five separate mistakes, six missiles contained nuclear warheads.

The chain of errors began the day before the flight when Air Force officers failed to inspect five bundles of cruise missiles inside a secure nuclear weapons hangar at Minot. Some missiles in the hangar have nuclear warheads, some have dummy warheads, while others have conventional weapons, officials said.

Maj-Gen Richard Newton, the US Air Force’s deputy chief of staff in charge of operations, told reporters that the ground crew grabbed the wrong bundle and loaded it on the plane.

On Aug. 30, the plane took off for Louisiana with the flight crew unaware that they were carrying enough destructive power to wipe out several cities.

Gen Newton, however, insisted that the military was never at risk of losing control of the warheads. The explanation apparently did not satisfy Secretary Gates who has ordered an outside panel headed by retired Gen Larry D. Welch, a former Air Force chief of staff, to review the Pentagon’s handling of nuclear weapons.

The cruise missiles were supposed to be transported to Barksdale without warheads as part of a treaty that requires the missiles to be mothballed.

Gen Newton said the warheads are normally removed in the Minot hangar before the missiles are assigned to a B-52 for transport.

The Air Force has fired four colonels who oversaw aircraft and weapons operations at Minot and Barksdale, and some junior personnel have also been disciplined, Gen Newton said. Despite the series of failures, Gen Newton said, the investigation found that human error, rather than inadequate procedures, were at fault.