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Saturday, September 13, 2014

Broken Arrows - USAF wins the trophy

"Broken Arrow" is the military term for an accidental event involving a nuclear weapon, but which does not create the risk for a nuclear war.  The 'accidental event' typically involves losing and/or damaging the weapon.

There have been 32 officially recognized "Broken Arrow" events in the United States since the dawn of nuclear weapons, as of Sept 2013.  Some of these events have been relatively minor, but others have been massive radiological accidents.  One accident with a large Hydrogen Bomb nearly made North Carolina uninhabitable... not that you would have seen THAT in the newspapers when it happened.  Apparently the news media were just as compliant in the 1950's as they are today.

I will go over a few of the more interesting Broken Arrow events.  Not surprisingly, most of these involve military aircraft crashing with weapons on board, as well as the intentional or inadvertent jettisoning of nuclear weapons.  All of these event descriptions are courtesy of Wikipedia.

On 14 February 1950, a Convair B-36B crashed in northern British Columbia after jettisoning a Mark 4 nuclear bomb - a production version of the very basic "Fat Man" device.  This was the first such nuclear weapon loss in history. The B-36 had been en route from Eielson Air Force Base near Fairbanks, Alaska to Carswell AFB in Fort Worth, Texas, on a mission that included a simulated nuclear attack on San Francisco.

Cold weather (−40 °F/−40 °C on the ground at Eielson AFB) adversely affected the planes involved in this exercise, and some minor difficulties with 44-92075 were noted before takeoff. Seven hours into the flight, three of the six engines began shooting flames and were shut down, and the other three engines proved incapable of delivering full power. The subsequent investigation blamed ice buildup in the mixture control air intakes.

The crew decided to abandon the aircraft because it could not stay aloft with three engines out of commission while carrying a heavy payload. The atomic bomb was jettisoned and detonated in mid-air, resulting in a large conventional explosion over the Inside Passage. The USAF later stated that the fake practice core on board the aircraft was inserted into the weapon before it was dropped.

One Broken Arrow event that couldn't be covered up was the fiery crash in 1966 of a B-52 bomber over Palomares, Spain.  Four thermonuclear (fusion) bombs were on board the aircraft at the time.  One weapon landed relatively intact, while one landed in the water, and was later recovered by the US Navy.

The remaining two weapons hit the ground and their conventional explosives detonated (Plutonium-based weapons need to explosively crush a hollow Plutonium sphere very precisely to detonate the weapon in a nuclear sense).  When the high explosives detonated due to the impact, they obliterated and scattered the Plutonium core.  The Plutonium, which is pyrophoric, caught fire.  This lofted the burning radiological contaminant (weapons grade Plutonium is both an alpha and neutron emitter) over about a 0.8 square mile area.  In effect, this was a "dirty bomb", where a conventional explosive scatters a radioactive contaminant.

Below, a graphic showing the locations the weapons fell at.
Where bombs fell
Wikipedia has an excellent article on the Palomares Broken Arrow, and this includes the Cold War international blowback.  There is still residual contamination of the soil, and Spain is now demanding that the U.S. perform additional clean-up.

Below, the hydrogen bomb after recovery from the ocean floor by the US Navy.

Below:  Empty casings of both the intact bombs that were recovered following the Palomares event.

Below:  Hundreds of 55 gallon drums containing Plutonium-contaminated soil awaiting shipment to the US for disposal.

The 1958 Mars Bluff, South Carolina Broken Arrow: 
On March 11, 1958 a U.S. Air Force Boeing B-47E-LM Stratojet from Hunter Air Force Base operated by the 375th Bombardment Squadron of the 308th Bombardment Wing near Savannah, Georgia, took off at approximately 4:34 PM and was scheduled to fly to the United Kingdom and then to North Africa as part of Operation Snow Flurry.  The aircraft was carrying nuclear weapons on board in the event of war with the Soviet Union breaking out.

Air Force Captain Bruce Kulka, who was the navigator and bombardier, was summoned to the bomb bay area after the captain of the aircraft, Captain Earl Koehler, had encountered a fault light in the cockpit indicating that the bomb harness locking pin did not engage. As Kulka reached around the bomb to pull himself up, he mistakenly grabbed the emergency release pin. The Mark 6 nuclear bomb dropped to the floor of the B-47 and the weight forced the bomb bay doors open, sending the bomb 15,000 ft (4,600 m) down to the ground below.

Below:  A MK 6 nuclear (simple fission) bomb, similar to the one in this story. 

Two sisters, six-year-old Helen and nine-year-old Frances Gregg, along with their nine-year-old cousin Ella Davies, were playing 200 yards (180 m) from a playhouse in the woods that had been built for them by their father Walter Gregg, who had served as a paratrooper during World War II. The playhouse was struck by the bomb. Its conventional high explosives detonated, destroying the playhouse, and leaving a crater about 70 feet (21 m) wide and 35 feet (11 m) deep. Fortunately, the fissile nuclear core was stored elsewhere on the aircraft.

All three girls were injured by the explosion, as as Walter, his wife Effie and son Walter, Jr. Seven buildings were damaged. The United States Air Force (USAF) was sued by the family of the victims and received $54,000 USD.  The incident made national and international headlines.  The crater is still present today, although overgrown by vegetation, and is marked by a historical marker; however, access to the site is limited because it is located on private property with no public access road.

The 1961 Goldsboro, North Carolina Broken Arrow:
The 1961 Goldsboro B-52 crash was an accident that occurred in Goldsboro, North Carolina, on January 24, 1961. A B-52 Stratofortress carrying two Mark 39 nuclear bombs broke up in mid-air, dropping its nuclear payload in the process.  The pilot in command ordered the crew to eject, which they did at 9,000 feet (2,700 m). Five men successfully ejected or bailed out of the aircraft and landed safely. Another ejected but did not survive the landing, and two died in the crash.  Controversy continues to surround the event as information newly declassified in 2013 reinforced long-held, public suspicions that one of the bombs came very close to detonating.

The first bomb hit the ground at nearly 700 miles per hour and buried itself in a tobacco field.  The Plutonium and Tritium were recovered, while the Uranium tamper was not.  The US Army Corps of Engineers purchased a 400ft. circular easement around the un-recovered portion of the bomb.

Coordinates for the easement around the first weapon:
Latitude: 35.493041°
Longitude: -77.859262°
(sorry don't know how to paste a Google Earth coordinate link yet!)

Below:  Recovery of a portion of the first bomb which had buried itself in the ground.

Below:  The second MK 39 themonuclear weapon that nearly destroyed Goldsboro, North Carolina.

This second bomb had deployed its chute, and three of the four steps required to detonate the weapon had activated.  These steps including charging the firing capacitors and deployment of the retarding parachute.   In 2013, information released as a result of a Freedom of Information Act request confirmed that a single switch prevented detonation of this 2.5 Megaton bomb.

According to Lt. Jack Revelle, the bomb disposal expert responsible for disarming the device, “As far as I’m concerned we came damn close to having a Bay of North Carolina. The nuclear explosion would have completely changed the Eastern seaboard if it had gone off.”   He also said the size of each bomb was more than 250 times the destructive power of the Hiroshima bomb, and large enough to have a 100% kill zone of seventeen miles.

Interactive Nuclear Weapon Blast Simulator.  Go to this website, enter Goldsboro North Carolina, and 2500 kiloton yield.  There definitely would have been a big smoking hole between Raleigh and Greenville.

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 (3,400 kg) Mark 15 nuclear bomb in the waters off Tybee Island near Savannah, Georgia, United States. During a practice exercise, the B-47 bomber carrying the bomb 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.

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. The damaged B-47 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 at 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 the nearest base, Hunter Air Force Base. The pilot, Colonel Howard Richardson, was awarded the Distinguished Flying Cross after this incident.

My comment:  It's amazing what you can get a medal for!

Some sources describe the bomb as a functional nuclear weapon, but others describe it as disabled. If the bomb had a plutonium nuclear core installed, it was a fully functional weapon. If the bomb had a dummy core installed, it was incapable of producing a nuclear explosion but could still produce a conventional explosion. 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 before 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 made of lead.  But 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 by 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.

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, the military announced the search had been unsuccessful. Based on 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 in their boat with a Geiger counter in tow. Secondary radioactive particles four times naturally occurring levels were detected and mapped, and the site of radiation origination triangulated. 

Subsequent investigations found the source of the radiation was natural.

Wikipedia also has a comprehensive list of nuclear accidents. Some of these are "Broken Arrows", some are accidental criticalities, and some are reactor accidents, all things we have discussed previously in this blog.

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