Michael Hoffman, Army Times, reports:

A B-52 bomber mistakenly loaded with six nuclear warheads flew from Minot Air Force Base, N.D., to Barksdale Air Force Base, La., on Aug. 30, resulting in an Air Force-wide investigation, according to three officers who asked not to be identified because they were not authorized to discuss the incident.

The B-52 was loaded with Advanced Cruise Missiles, part of a Defense Department effort to decommission 400 of the ACMs. But the nuclear warheads should have been removed at Minot before being transported to Barksdale, the officers said. The missiles were mounted onto the pylons of the bomber’s wings.

Advanced Cruise Missiles carry a W80-1 warhead with a yield of 5 to 150 kilotons and are specifically designed for delivery by B-52 strategic bombers.

Air Force spokesman Lt. Col. Ed Thomas said the transfer was safely conducted and the weapons were in Air Force custody and control at all times.

However, the mistake was not discovered until the B-52 landed at Barksdale, which left the warheads unaccounted for during the approximately 3 1/2 hour flight between the two bases, the officers said.

An investigation headed by Maj. Gen. Douglas Raaberg, director of Air and Space Operations at Air Combat Command Headquarters, was launched immediately to find the cause of the mistake and figure out how it could have been prevented, Thomas said.

Air Force officials wouldn’t officially specify whether nuclear weapons were involved, in accordance with long-standing Defense Department policy regarding nuclear munitions, Thomas said. However, the three officers close to the situation did confirm the warheads were nuclear.

Officials at Minot immediately conducted an inventory of its nuclear weapons after the oversight was discovered, and Thomas said he could confirm that all remaining nuclear weapons at Minot are accounted for.

“Air Force standards are very exacting when it comes to munitions handling,” he said. “The weapons were always in our custody and there was never a danger to the American public.”

At no time was there a risk for a nuclear detonation, even if the B-52 crashed on its way to Barksdale, said Steve Fetter, a former Defense Department official who worked on nuclear weapons policy in 1993-94. A crash could ignite the high explosives associated with the warhead, and possibly cause a leak of the plutonium, but the warheads’ elaborate safeguards would prevent a nuclear detonation from occurring, he said.

“The main risk would have been the way the Air Force responded to any problems with the flight because they would have handled it much differently if they would have known nuclear warheads were onboard,” he said.

The risk of the warheads falling into the hands of rogue nations or terrorists was minimal since the weapons never left the United States, according to Fetter and Michael O’Hanlon, a senior fellow at the Brookings Institution, an independent research and policy think tank in Washington, D.C.

The crews involved with the mistaken load at the 5th Bomb Wing at Minot have been temporarily decertified from performing their duties involving munitions pending corrective actions or additional training, Thomas said.

Air Combat Command will have a command-wide mission stand down Sept. 14 to review their procedures in response to this oversight, he said.

“The Air Force takes its mission to safeguard weapons seriously,” he said. “No effort will be spared to ensure that the matter is thoroughly and completely investigated.”