The lost Tybee H-bomb is still buried off Georgia

A 7,600-pound Mark 15 hydrogen bomb has lain somewhere in Wassaw Sound off Tybee Island, Georgia, since 5 February 1958, when a B-47 crew jettisoned it after a mid-air collision with an F-86 fighter during a night training exercise.

The F-86’s pilot ejected; the damaged bomber, flown by Howard Richardson, could not slow down enough to land safely with the weapon aboard, so it was dropped from about 7,200 feet before the B-47 landed at Hunter Air Force Base. Searchers combed a three-square-mile area until 16 April 1958, when the bomb was declared irretrievably lost.

Could the Tybee bomb explode?

Not as a nuclear weapon, if the paperwork is right. The Defense Department’s official accident summary states that a nuclear detonation was impossible because the capsule — the fissile core — was not aboard. Richardson signed an Atomic Energy Commission custodian receipt before take-off, and the word “simulated” was scribbled on the line reportedly covering the capsule. Doubt lingered because in 1966 W.J. Howard, a Pentagon atomic-energy official, wrote to Congress’s Joint Committee on Atomic Energy that it had been a “complete weapon”; he later retracted that after the Air Force sent him contrary data. One error persists: the Air Force still says the bomb had no “plutonium” pit, when the Mk 15’s pit was highly enriched uranium.

How powerful was it?

Estimates differ. HistoryNet gives the Mod 0 version a 1.69-megaton yield; the Center for Arms Control cites up to 3.8 megatons — about 190 times the bomb that destroyed Nagasaki. Even without a core, the bomb carried about 400 pounds of conventional explosive.

A 2001 Air Force reassessment concluded that, if intact, that explosive would pose no hazard where it lies, probably under 5 to 15 feet of silt. In 2004 a private search team reported radiation readings seven to ten times normal nearby, later attributed to naturally occurring minerals.