The United States abandoned a nuclear weapon beneath the ice in northern Greenland following a crash in 1968, a BBC investigation has found.
Its unique vantage point – perched at the top of the world – has meant that Thule Air Base has been of immense strategic importance to the US since it was built in the early 1950s, allowing a radar to scan the skies for missiles coming over the North Pole.
The Pentagon believed the Soviet Union would take out the base as a prelude to a nuclear strike against the US and so in 1960 began flying “Chrome Dome” missions. Nuclear-armed B52 bombers continuously circled over Thule – and could head straight to Moscow if they witnessed its destruction.
Greenland is a self-governing province of Denmark but the carrying of nuclear weapons over Danish territory was kept secret.
But on 21 January 1968, one of those missions went wrong.
In the aftermath, military personnel, local Greenlanders and Danish workers rushed to the scene to help.
Eventually, a remarkable operation would unfold over the coming months to recover thousands of tiny pieces of debris scattered across the frozen bay, as well as to collect some 500 million gallons of ice, some of it containing radioactive debris.
The documents make clear that within weeks of the incident, investigators piecing together the fragments realised that only three of the weapons could be accounted for.
Even by the end of January, one document talks of a blackened section of ice which had re-frozen with shroud lines from a weapon parachute. “Speculate something melted through ice such as burning primary or secondary,” the document reads, the primary or secondary referring to parts of the weapon.
By April, a decision had been taken to send a Star III submarine to the base to look for the lost bomb, which had the serial number 78252. (A similar submarine search off the coast of Spain two years earlier had led to another weapon being recovered.)
But the real purpose of this search was deliberately hidden from Danish officials.
One document from July reads: “Fact that this operation includes search for object or missing weapon part is to be treated as confidential NOFORN”, the last word meaning not to be disclosed to any foreign country.
“For discussion with Danes, this operation should be referred to as a survey repeat survey of bottom under impact point,” it continued.