Then came a surprise. The computer simulations showed that at a certain point from stockpile to target, the weapon would “fail catastrophically,” according to Bruce T. Goodwin, principal associate director at Livermore for weapons programs. Such a failure would mean that the weapon would not produce the explosive yield expected by the military — either none at all, or something quite different than required to properly hit the target.

“So we went in and thoroughly investigated that, and determined that the way the weapon is handled by the military had to be changed, or you would be susceptible to having the weapons fail catastrophically when, God forbid, they should ever be used,” Goodwin said. He added that the fault occurred in the “real dynamics of the vehicle” — a term describing the weapon’s trajectory and behavior — and could not have been revealed by underground explosive testing or by examining the components.

Following the discovery and a multi-year effort, the B-83 bombs and the military’s handling procedures for the weapons have been fixed, officials said.