1958 Tybee Island mid-air collision
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 (3,400 kg) 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 protect the aircrew from a possible detonation in the event of a crash, the bomb was jettisoned. Following several unsuccessful searches, the bomb was presumed lost somewhere in Wassaw Sound off the shores of Tybee Island.
Accident
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 (3,400 kg) 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 from exploding during an emergency landing. Permission was granted and the bomb was jettisoned at 7,200 feet (2,200 m) 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 Air Force Base, later Hunter Army Air Field. The pilot, Colonel Howard Richardson, was awarded the Distinguished Flying Cross after this incident for his role in piloting the B-47.
Bomb
The 12-foot (4 m) long Mark 15 bomb weighs 7,600 pounds (3,400 kg) and bears the serial number 47782. It contains 400 pounds (180 kg) of conventional high explosives and highly enriched uranium. The Air Force maintains that the bomb's nuclear capsule, used to initiate the nuclear reaction, was removed prior to its flight aboard B-47. As noted in the Atomic Energy Commission "Form AL-569 Temporary Custodian Receipt (for maneuvers)" signed by the aircraft commander, the bomb contained a simulated 150 pound cap which was made of lead. However, according to 1966 Congressional testimony by then Assistant Secretary of Defense W.J. Howard, the Tybee Island bomb was a "complete weapon, a bomb with a nuclear capsule," and one of two weapons lost up to that time that contained a plutonium trigger. Nevertheless, a study of the Strategic Air Command documents indicates that in February 1958, Alert Force test flights (with the older Mark 15 payloads) were not authorized to fly with nuclear capsules on board. Such approval was pending deployment of safer "sealed-pit nuclear capsule" weapons that did not begin deployment until June 1958.
Recovery efforts
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. 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 (2 to 5 m) of silt at the bottom of Wassaw Sound. In 2004, retired Air Force Colonel Derek Duke claimed to have narrowed the possible resting spot of the bomb to a small area approximately the size of a football field. He and his partner located the area by trawling the area in their boat with a Geiger counter in tow. Secondary radioactive particles 4 times the naturally occurring levels were detected and mapped, and the site of radiation origination triangulated. Subsequent investigations found the source of the radiation was natural. In any case, a geiger counter is not efficient in detecting the alpha radiation from enhanced uranium.
Ongoing concerns
The risk of corrosion of the alloy casing of the bomb is less if it is completely covered in sand. But if part of the alloy casing of the bomb is exposed to seawater due to the shifting strata in which it is buried, 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. Storms, hurricanes, and strong currents frequently change the sands of the continental shelf near Tybee Island. To date, no undue levels of unnatural radioactive contamination (over and above the already high levels thought to be due to monazite, a locally occurring sand which is naturally high in radiation) have been detected in the regional Upper Floridan aquifer by the Georgia Department of Natural Resources. This event, as well as the 1956 B-47 disappearance, were the basis for NCIS Episode "Broken Arrow," which aired in 2010.
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 (3,400 kg) 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 protect the aircrew from a possible detonation in the event of a crash, the bomb was jettisoned. Following several unsuccessful searches, the bomb was presumed lost somewhere in Wassaw Sound off the shores of Tybee Island.
Accident
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 (3,400 kg) 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 from exploding during an emergency landing. Permission was granted and the bomb was jettisoned at 7,200 feet (2,200 m) 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 Air Force Base, later Hunter Army Air Field. The pilot, Colonel Howard Richardson, was awarded the Distinguished Flying Cross after this incident for his role in piloting the B-47.
Bomb
The 12-foot (4 m) long Mark 15 bomb weighs 7,600 pounds (3,400 kg) and bears the serial number 47782. It contains 400 pounds (180 kg) of conventional high explosives and highly enriched uranium. The Air Force maintains that the bomb's nuclear capsule, used to initiate the nuclear reaction, was removed prior to its flight aboard B-47. As noted in the Atomic Energy Commission "Form AL-569 Temporary Custodian Receipt (for maneuvers)" signed by the aircraft commander, the bomb contained a simulated 150 pound cap which was made of lead. However, according to 1966 Congressional testimony by then Assistant Secretary of Defense W.J. Howard, the Tybee Island bomb was a "complete weapon, a bomb with a nuclear capsule," and one of two weapons lost up to that time that contained a plutonium trigger. Nevertheless, a study of the Strategic Air Command documents indicates that in February 1958, Alert Force test flights (with the older Mark 15 payloads) were not authorized to fly with nuclear capsules on board. Such approval was pending deployment of safer "sealed-pit nuclear capsule" weapons that did not begin deployment until June 1958.
Recovery efforts
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. 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 (2 to 5 m) of silt at the bottom of Wassaw Sound. In 2004, retired Air Force Colonel Derek Duke claimed to have narrowed the possible resting spot of the bomb to a small area approximately the size of a football field. He and his partner located the area by trawling the area in their boat with a Geiger counter in tow. Secondary radioactive particles 4 times the naturally occurring levels were detected and mapped, and the site of radiation origination triangulated. Subsequent investigations found the source of the radiation was natural. In any case, a geiger counter is not efficient in detecting the alpha radiation from enhanced uranium.
Ongoing concerns
The risk of corrosion of the alloy casing of the bomb is less if it is completely covered in sand. But if part of the alloy casing of the bomb is exposed to seawater due to the shifting strata in which it is buried, 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. Storms, hurricanes, and strong currents frequently change the sands of the continental shelf near Tybee Island. To date, no undue levels of unnatural radioactive contamination (over and above the already high levels thought to be due to monazite, a locally occurring sand which is naturally high in radiation) have been detected in the regional Upper Floridan aquifer by the Georgia Department of Natural Resources. This event, as well as the 1956 B-47 disappearance, were the basis for NCIS Episode "Broken Arrow," which aired in 2010.
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