Thursday, February 10, 2011

1958 Tybee Island B-47 Crash

The Tybee Island B-47 crash was an incident on February 5, 1958, in which the United States Air Force lost a 7,600-pound Mark 15 hydrogen bomb in the waters off Tybee Island near Savannah, Georgia, USA. During a practice exercise the B-47 bomber carrying it collided in midair with an F-86 fighter plane. To prevent a detonation in the event of a crash and to save the aircrew, the bomb was jettisoned. Following several unsuccessful searches, the bomb was presumed lost somewhere in Wassaw Sound off the shores of Tybee Island.

The B-47 bomber was on a simulated combat mission from Homestead Air Force Base in Florida. It was carrying a single 7,600-pound bomb. At about 2:00 AM, the B-47 collided with an F-86. The F-86 crashed after the pilot ejected from the plane, but the B-47, despite being damaged, remained airborne, albeit barely. The crew requested permission to jettison the bomb in order to reduce weight and prevent the bomb exploding during an emergency landing. Permission was granted and the bomb was jettisoned at 7,200 feet while the bomber was traveling about 200 knots (370 km/h). The crew did not see an explosion when the bomb struck the sea. They managed to land the B-47 safely at Hunter Army Air Field.

Starting on February 6, 1958, the Air Force 2700th Explosive Ordnance Disposal Squadron and 100 Navy personnel equipped with hand held sonar and galvanic drag and cable sweeps mounted a search for the bomb. On April 16, 1958 the military announced that the search efforts had been unsuccessful. Based upon a hydrologic survey, the bomb was thought by the Department of Energy to lie buried under 5 to 15 feet of silt at the bottom of Wassaw Sound.

In 2001, the United States Air Force conducted a study to determine whether the bomb posed a threat to residents of the surrounding area. The Air Force says with certainty that the bomb contains conventional explosives and highly enriched uranium, which could pose an environmental or proliferation threat. The Air Force determined that it was prudent to leave the bomb covered in mud at the bottom of the sea floor rather than disturb it and risk the potential of detonation or contamination.

The risk of corrosion of the alloy casing of the bomb is less if it is completely covered in sand. But if, due to the shifting strata in which it is buried, part of the alloy casing of the bomb is exposed to seawater, rapid corrosion could occur, as demonstrated in simulation experiments. Eventually, the highly enriched uranium could be leached out of the device and enter the aquifer that surrounds the continental shelf in this area. Frequent storms, hurricanes, and strong currents frequently change the sands of the continental shelf near Tybee Island.