Newly released government documents reveal that a 42,000-pound hydrogen bomb, one of the most powerful ever made, accidentally fell from a bomber near Albuquerque 29 years ago, a newspaper said today.
Non-nuclear explosives, which are used to trigger armed nuclear devices, detonated in the unarmed Mark 17 bomb when it hit the ground 4 1/2 miles south of Kirtland Air Force Base's control tower, the Albuquerque Journal reported.
The newspaper said it obtained the documents through the Freedom of Information Act.
No one was injured when the bomb hit an uninhabited area owned by the University of New Mexico, creating a crater about 12 feet deep and 25 feet in diameter, the newspaper said.
The documents said minor radioactive contamination was detected in the crater.
"It is possibly the most powerful bomb we ever made," said Stan Norris, a research associate with the Natural Resources Defense Council and a specialist on nuclear weapons.
The government documents did not show the exact explosive yield of the bomb, but Norris said most researchers believe that it was more than 10 megatons. A megaton is the equivalent of 1 million tons, or 1,000 kilotons, of TNT.
Norris said the largest nuclear weapon in the U.S. arsenal today has a yield of about 9 megatons.
The atomic bomb dropped on Hiroshima in World War II had a yield of about 16 kilotons.
The "Nuclear Weapons Databook" said the Mark 17 was "the first droppable thermonuclear bomb to be tested." The Mark 17, made at Los Alamos National Laboratory in 1952, was 24 1/2 feet long and 5 feet in diameter.
The Mark 17 "was very primitive by today's standards, in terms of safety devices," Norris said. "But it didn't go off, and we don't know how serious the accident was."
The Mark 17 fell from an Air Force B-36 bomber flying to Kirtland from Biggs Army Air Field in Texas on May 22, 1957, the documents said.
The government first reported the accident in 1981 in a brief release saying only that a nuclear weapon of some kind had been dropped.
The documents obtained by the Journal contain the first publicly disclosed description of the type of weapon involved and why the accident occurred.
The exact reason why the bomb fell from the airplane, taking the bomb-bay doors with it, was not given. But the government documents indicate that a safety release mechanism apparently was moved to the wrong position.
The bomb was "supported in the bomb bay by means of a 'wraparound' sling that is releasable at one of its ends by means of a release mechanism," a 1957 Defense Department document said.
Once a safety pin is removed, the sling could be released by a cockpit manual release connected by wire to the release mechanism, the document said.
A protective cover enclosed the wire near the release mechanism. But the sling had been repositioned and the cover was moved, causing a length of the manual release wire to be exposed, it said.
The last paragraph of the document, which may have explained what happened to the exposed and unprotected release wire, was edited out of the document released to the Journal.