The Nation; Chain of errors blamed for nuclear arms going undetected; Air Force inquiry says officers failed five times to check missiles before a flight to another base.

Air Force weapons officers assigned to secure nuclear warheads failed on five occasions to examine a bundle of cruise missiles headed to a B-52 bomber in North Dakota, leading the plane's crew to unknowingly fly six nuclear-armed missiles across the country.

That August flight, the first known incident in which the military lost track of its nuclear weapons since the dawn of the atomic age, lasted nearly three hours, until the bomber landed at Barksdale Air Force Base in northern Louisiana.

But according to an Air Force investigation presented to Defense Secretary Robert M. Gates on Friday, the nuclear weapons sat on a plane on the runway at Minot Air Force Base in North Dakota for nearly 24 hours without ground crews noticing the warheads had been moved out of a secured shelter.

"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."

For decades, it has been military policy to never discuss the movement or deployment of the nuclear arsenal. But Wynne said the accident...