Although the flight took place a week ago, news of the incident has only just come to light.
The B-52 took off from Minot Air Force Base in North Dakota, landing at Barksdale Air Force Base in Louisiana more than three hours later. It was only then that crews discovered that the six cruise missiles mounted on the bombers' wings were armed with W80-1 warheads, which have yields of between 5 and 150 kilotons of TNT equivalent.
An Air Force spokesman, Lt. Col. Edward Thomas, claimed that the flight had at no time posed a threat to public safety. Sources in the U.S. military, speaking anonymously due to a ban on official discussion of nuclear weapons, said that the launch of the missiles was only possible through a complex, multistage procedure.
The Air Force has started an investigation into the incident, headed by Major-General Douglas Raaberg, director of Air and Space Operations at Air Combat Command Headquarters. It has also ordered the grounding of all bombers and fighter planes on September 14 to review procedures.
A squadron commander in charge of the warheads, each of which has up to ten times the destructive power of the Hiroshima atom bomb, has been relieved of his duties, while crews responsible for the error have been banned from handling nuclear munitions.
U.S. Rep. Edward Markey, a senior member of the Homeland Security committee, called the flight "absolutely inexcusable."
"Nothing like this has ever been reported before and we have been assured for decades that it was impossible," Markey said.