“Broken Arrow” is the military’s code word for an accident involving a nuclear weapon. Since 1950, there have been almost three dozen acknowledged “Broken Arrow” incidents. Six times, the US has lost a nuclear weapon in an accident that it was unable to recover, including a Navy plane that crashed into Puget Sound with a nuclear depth charge, and an attack plane that rolled off a carrier near Japan and sank with its B43 nuclear bomb. Several times, nuclear weapons have been dropped or accidentally released near American cities. In many of these, the nuclear weapon’s conventional explosives actually detonated, and only the bomb’s safety precautions prevented a nuclear explosion.
In the early years of the Cold War, the US Air Force Strategic Air Command was on 24-hour duty, prepared to retaliate at any time to a Soviet nuclear attack. As part of their training, US Air Force bombers would make practice flights across the country and around the world, carrying nuclear weapons. For safety, the plutonium cores that triggered the nuclear explosion were removed and either stored separately in the airplane (in a metal rack known as “the birdcage”) or kept on the ground. Later, the Strategic Air Command began putting portions of its bomber force on “airborne alert”, circling in the air with live (but “safed”) nuclear weapons: it was intended to protect the bombers from being caught on the ground in a surprise Russian attack.
In February 1950, a B-36 Peacemaker strategic bomber was scheduled to make a training flight, taking off from Alaska and making a mock bombing run in Texas before returning. The Peacemaker carried one Mark 4 nuclear bomb, with the plutonium core removed. As the bomber crossed over Canada, however, ice began to clog the engine carburetors, and three engines had to be shut down. As the remaining engines began to lose power, the crew realized that the plane could not make it to safety. Steering the bomber out over the Pacific Ocean, the pilot jettisoned the nuclear weapon. The Mark 4’s conventional explosives detonated on impact and the bomb was destroyed. The crew then turned back over land and bailed out. Twelve of the seventeen airmen were rescued. The B-36 flew on autopilot for a short time until it crashed into a remote mountain in British Columbia.
As it turned out, 1950 was a bad year for the Air Force. The Korean War was raging, and the US had made the secret decision to move a number of atomic bombs to staging areas in Asia where they could be readied for possible use. In April, a B-29 Superfortress took off from a base in New Mexico, bound for Guam. It was carrying General Robert Travis and a number of other officers. It was also carrying a Mark 4 bomb. When the plane developed engine trouble, it tried to make an emergency landing, but the landing gear was disabled. The resulting crash set off the 2.5 tons of conventional explosive inside the Mark 4, killing a number of people on the plane and on the ground, including General Travis.
Three months later, a B-50 Superfortress (a modified version of the B-29) in Ohio crashed during a training flight, and in August a B-29 failed to make an emergency landing in California. In both of these cases, the resulting fire set off the conventional explosives in the nuclear bombs they had been carrying. Then in November 1950, a USAF B-50 experienced engine failure while flying over Canada. Before making an emergency landing, the crew set their nuclear weapon to self-destruct and dropped it over the St Lawrence River in Quebec. Although the bomb did not contain a nuclear core, it was destroyed when its explosives detonated.
In May 1957, a B-36 carrying a Mark 17 hydrogen bomb was making a landing approach at a base just outside of Albuquerque NM when the bomb broke loose, tore through the bomb bay doors, and fell onto a cattle ranch. The implosion explosives detonated on impact, killing one of the cows, but although the plane was carrying a plutonium core for the Mark 17, it was separated in the “birdcage” and was not inside the bomb.
Later in 1957, a C-124 cargo plane with engine trouble was forced to jettison two of the three nuclear weapons it was carrying, dropping them off the Jersey shore, and in another incident a B-47 crashed on landing in Florida, with the resulting fire detonating the conventional explosives in the nuclear bomb it carried. In both cases, the plane had also been carrying plutonium cores.
The year 1958 was also not a good one for the USAF. There were five Broken Arrows that year, including one of the most famous.
One of the most potentially serious accidents happened in January at a base in Morocco. A B-47 was taking off on a training mission carrying a nuclear weapon with its plutonium core intact and installed in the bomb, though the weapon’s electrical system had been “safed”. A tire blew on takeoff, the tail hit the ground, and the fuel tank caught on fire. Remarkably, the bomb’s conventional explosives did not detonate.
One of the best-known Broken Arrows in the US happened a month later. While conducting a mock practice bombing run on Savannah GA, a B-47 bomber was intercepted by an F-86 fighter who was also on a training mission. Somehow, the two planes collided in the dark, and the crew of the crippled B-47 jettisoned their weapon, a Mark 15 hydrogen bomb, just off the coast, where it fell somewhere off the mouth of the Savannah River near Tybee Island. Despite several search attempts, the bomb was never recovered.
Just a month later, another B-47 was flying over the town of Florence SC when the shackles in the bomb bay failed, and a nuclear bomb tore through the bomb bay doors and fell out of the airplane. Several people on the ground were injured when the impact detonated the bomb’s explosives.
There were two incidents in November 1958. First a B-47 crashed on takeoff in Texas, with the resulting fire setting off the explosives in the nuclear bomb it was carrying. Then another B-47 burned on the ground in Louisiana. This time the explosives did not detonate, though the nuclear bomb was destroyed in the fire.
Another well-known Broken Arrow happened in January 1961. A B-52 Stratofortress was flying airborne alert over the city of Goldsboro NC, with two intact but “safed” Mark 39 hydrogen bombs, when it developed a fuel leak that led to an explosion, destroying the plane. Both of the Mark 39s fell free, with one of them deploying its parachute and landing undamaged. The second bomb’s parachute failed, and it broke apart on impact, scattering pieces over a wide area. The thermonuclear “second stage” of the bomb was never found, but enough of the wrecked Mark 39 was recovered for the Air Force to determine that five of the bomb’s six electrical switches had been triggered, and only the manual sixth “safe” had prevented the 20-megaton nuclear explosion.
What is probably the most famous Broken Arrow incident happened in January 1966. A B-52 on airborne alert over the Mediterranean was refueling from a tanker plane for its return to the US when the two jets collided. The Stratofortress was carrying four safed B-28 hydrogen bombs, which fell near the town of Palomares, Spain. Two of the B-28s detonated their explosives on impact, scattering radioactive material over a large area. One of the remaining bombs was found in a streambed. The other one fell into the Mediterranean, where it was found by a local fisherman (who negotiated with the Air Force for payment of salvage rights).
The last known Broken Arrow happened in January 1968. A B-52 was flying an airborne alert over Greenland when a fire broke out, forcing the crew to make an emergency landing at the US base in Thule. The bomber crashed short of the runway. One of the four hydrogen bombs aboard detonated its conventional explosives. Two of the bombs melted right through the pack ice and fell into the arctic ocean below. One of these was found on the seafloor 11 years later; the other was never found at all.
After 1968 the Air Force ended its practice of “airborne alerts”. Since then, there have been no known Broken Arrow incidents involving nuclear bombs. The last known American nuclear weapons accident happened in 1980, when a Titan II intercontinental ballistic missile in Arkansas exploded during maintenance (a mechanic dropped a wrench and punctured a fuel tank), blowing the ICBM’s 9-megaton warhead completely out of the silo.