Who hasn’t misplaced something? We waste so much time looking for car keys, reading glasses, and the television remote. We turn over every seat cushion and look under the sofa, only to discover the missing item was in plain view all along.

If that has happened to you, try to be a little forgiving as you learn about that time the United States lost one of its nuclear weapons — and still has been unable to find it.

Broken Arrow

It was a routine mission. It was as routine, that is, for any mission that involves carrying four hydrogen bombs on an airplane. On January 21, 1968, that’s what the crew of a U.S. B-52 bomber was doing as it patrolled the territory over Greenland and Baffin Bay. In those days, as many as a dozen bombers were on 24-hour airborne alert as part of Operation Chrome Dome. It was designed to offer an effective response to any Soviet nuclear attack.

The mission stopped being routine when a fire broke out in the cabin six hours into the mission. Despite heroic efforts to save the plane, the B-52 crashed into the ice about 8 miles (13 km) south of the U.S. airbase at Thule. One of the 7-member crew was killed.

The crash triggered an explosion among the weapons. Fortunately, it was not a nuclear detonation. Instead, the non-nuclear explosive elements detonated on impact, sending the payload flying in all directions.

The explosion also breached the containers that held the nuclear material for the weapons. As a result, about 10 Tera-Becquerel (Tera = trillion) of radioactive plutonium was spread over an area of 2.97 square miles (7.68 km²). As if that weren’t enough, the contamination also included significant amounts of uranium, americium, and tritium.

The heat from the blast and radiation made short work of the ice. When it melted, Bylot Sound became contaminated with about 5 Giga-Becquerel (Giga = billion) of radioactive plutonium. The wind carried radioactive contamination south to the settlement of Narssarssuk, about 4.35 miles (7 km) from the crash site.

In the span of a few terrifying seconds, the U.S. had its newest “Broken Arrow” – a U.S. military term that describes a major accident or loss of a nuclear weapon.

Project Crested Ice

Although Thule is a U.S. airbase, Greenland is a territory of Denmark. Suddenly, the U.S. found itself in a diplomatic kerfuffle with a nation that had declared itself to be nuclear-weapon-free.

The U.S. government immediately started cleanup and recovery operations under the code name “Project Crested Ice.” It was known informally as “Dr. Freezelove.” The details of the endeavor are in this declassified 214-page document. By the time Crested Ice wrapped up, an estimated 93% of the contamination was removed, and 147 freight cars of radioactive waste were shipped back to the USA. The remaining radioactive material was distributed so widely that recovery was impractical. A 1995 survey found 410 deaths due to cancer out of a sample of 1,500 Danish workers.

The majority of efforts of the personnel of Project Crested Ice were directed at cleanup. At the same time, military leaders pushed to get some answers about the status of the four hydrogen bombs that were in the payload.

Strategic Air Command issued statements to reassure the public that all four weapons had been recovered. Despite this, rumors circulated that at least one of the bombs was still out there somewhere. It wasn’t until 2008, when the BBC acquired declassified documents through the Freedom of Information Act, that it was confirmed that the rumors were true. Within three weeks of the crash, authorities knew they had recovered only three of the hydrogen bombs. A report written six months after the incident concluded, “An analysis by the AEC of the recovered secondary components indicates recovery of 85 percent of the uranium and 94 percent, by weight, of three secondaries. No parts of the fourth secondary have been identified.”

After the news of the missing weapon became public knowledge, the BBC interviewed former nuclear-weapons engineer William H. Chambers. He justified the decision to abandon the search for the missing nuke, saying, “There was disappointment in what you might call a failure to return all of the components … it would be very difficult for anyone else to recover classified pieces if we couldn’t find them.”

Details of this and other frightening situations can be found in this declassified 43-page report from the Department of Defense that summarizes accidents involving U.S. nuclear weapons between 1950 and 1980.

Catastrophe By Seat Cushion

An investigation into the origins of the disaster revealed a curious and disturbing cause: a seat cushion.

The cold conditions of Greenland are exacerbated when flying in a military aircraft that was not designed for comfort. Investigators learned that the crew of the B-52 tried to compensate for “frozen buns” by bringing seat cushions on their missions. On this fateful day, three cloth-covered foam cushions were placed under the instructor navigator’s seat. Unfortunately, the placement of the cushions blocked a heating vent.

During a scheduled mid-air refueling, a crew member took up his position at the instructor navigator’s seat. He found it to be uncomfortably cold, so he opened an engine bleed to draw in hot air from the engine. The heated air, brought into direct and prolonged contact with the seat cushions, triggered a fire. By the time this was discovered, the aircraft was doomed.

Ironically, nearly a decade earlier, the U.S. conducted a detailed investigation to see if the meltdown of a nuclear reactor had been caused by “goosing” or butt-pinching. It concluded that its reactors were safe from such shenanigans. Sadly, the study did not address what it would take to stop a seat cushion from triggering a nuclear disaster.

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