The US Air Force has launched an investigation after a B-52 bomber flew across the US last week mistakenly loaded with nuclear-armed missiles.
Air Force officials have been quick to insist that the public was never in any danger and that the weapons - the nature of which they declined officially to specify - remained in secure custody at all times.
Officials are nevertheless likely to be deeply concerned that the weapons in effect went missing from the time they were accidentally mounted on to the pylons of the B-52's wings until the oversight was discovered on landing at Barksdale Air Force Base in Louisiana three-and-a-half hours later.
The episode was first reported by the Military Times, which said five warheads had gone missing, and subsequently confirmed by the Pentagon, which said the number of warheads was in fact six.
The chairman of the House Armed Services Committee, Ike Skelton, called the incident "deeply disturbing" and said he would be pressing the military for more details.
Missing nuclear warheads have been a staple of nightmare-scenario popular fiction ever since the dawn of the atomic age. One of America's top stated national security priorities is ensuring that a nuclear warhead or warheads - from any of the world's nuclear powers - does not go missing and fall into the hands of a sophisticated guerrilla group such as al-Qa'ida.
Although there was never any question of these particular warheads falling into enemy hands, the security lapse in and of itself is likely to be viewed as troubling.
"The American people, our friends, and our potential adversaries must be confident that the highest standards are in place when it comes to our nuclear arsenal," Mr Skelton said.
According to the Military Times, the warheads were mounted on a class of advanced cruise missile that is being decommissioned. The intention was to transfer the missiles to Barksdale without the warheads. But the munitions team with the 5th Bomb Wing at Minot Air Force Base in North Dakota appears to have forgotten to remove the warheads.
Military experts agreed it was highly unlikely that the W80-1 nuclear warheads could have detonated, even if the plane had crashed, because of the elaborate safeguard mechanisms associated with nuclear devices. But a crash could have caused the high explosives associated with the warheads to detonate. Some of the plutonium inside the warheads could also have leaked out, creating a potential public health hazard, Steve Fetter, a nuclear expert, told the Military Times.
The W80-1 warhead carries a yield of between five and 150 kilotons. By comparison, the bomb dropped on Hiroshima in 1945 measured roughly 15 kilotons.
A major-general who runs air and space operations at the Air Force's Air Combat Command Headquarters will now conduct a full investigation into the incident. The team responsible for the missile loading at Minot have been suspended from munitions duties pending further training, Ed Thomas, an Air Force spokes-man, said. Mr Thomas sought to minimise the risks that the incident exposed. "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."
He added: "The Air Force takes its mission to safeguard weapons seriously. No effort will be spared to ensure that the matter is thoroughly and completely investigated."