A newly declassified trove of Cold War-era documents has unveiled a decades-long secret at the icy heart of NATO’s northern frontier: Denmark, long a staunch advocate of non-nuclear policy, secretly allowed the United States to store and fly nuclear weapons from its territory in Greenland. The revelations, published yesterday by the National Security Archive, challenge official histories, expose covert deals at the highest levels of government, and reignite questions about Denmark’s true role in Cold War nuclear strategy.
The document collection, The United States and Greenland, Part I: Episodes in Nuclear History 1947–1968, lays bare the extent to which American military planners operated in Greenland with almost total freedom — and how Danish officials, while publicly upholding a nuclear-free stance, privately enabled those operations.
A Secret “Green Light” to Go Nuclear
At the centre of the story is Danish Prime Minister Hans Christian Hansen’s clandestine approval in 1957 for the United States to store nuclear weapons at Thule Air Base in northwest Greenland. According to declassified U.S. State Department correspondence, Hansen responded to a U.S. inquiry about potential objections to nuclear deployments not with opposition, but with silence — and a vague, non-committal document interpreted by both sides as implicit consent. He requested secrecy, recognising the political danger such an arrangement posed.
Publicly, Hansen and successive Danish governments upheld a strict policy: Denmark would not allow nuclear weapons on its soil “under the present conditions.” Behind the scenes, however, they created what scholars now call a “double standard” — forbidding nuclear deployments in Denmark proper while making Greenland, then a county within the Danish realm, an exception.
The 1951 U.S.-Danish defence agreement, which superseded wartime arrangements, gave Washington sweeping access to Greenland’s territory and airspace. As one State Department official put it bluntly in 1955, the U.S. could do “almost anything, literally, that we want to in Greenland.”
A Nuclear Outpost in the Arctic
In 1958, the U.S. Strategic Air Command (SAC) quietly stationed nuclear bombs at Thule — two Mark 6 atomic bombs, two MK 36 thermonuclear weapons, and additional components. The storage was short-lived, but it wasn’t the end of America’s nuclear footprint in Greenland.
Between 1958 and 1965, the U.S. maintained 48 nuclear warheads at Thule for Nike-Hercules air defence missiles. There were also likely deployments of nuclear-armed Falcon missiles, though exact numbers remain unknown. These deployments stood in direct contradiction to Denmark’s professed policies, but went unchallenged — and unknown to the Danish public — for decades.
More alarming were the U.S. overflights. As part of the SAC’s “Chrome Dome” programme, nuclear-armed B-52 bombers flew daily patrols across the Arctic — including routes directly over Greenland — ready to strike the Soviet Union if war broke out. By 1961, these “airborne alerts” included sorties to monitor the Ballistic Missile Early Warning System (BMEWS) radar site at Thule, considered critical to detecting Soviet missile launches.
Danish officials knew of the overflights but largely looked the other way. Some officials, like Greenland Under Secretary Eske Brun, privately raised concerns about nuclear accidents. But when asked directly by Danish diplomats, U.S. ambassadors downplayed the risk, asserting the flights were consistent with the 1951 agreement.
The 1968 Thule Crash: Secrets Come Crashing Down
On 21 January 1968, the fragile balance of secrecy and acquiescence shattered.
A U.S. B-52 bomber on airborne alert caught fire mid-flight due to a malfunctioning heating system, igniting foam cushions on board. The crew bailed out; one member died. The aircraft crashed near Thule Air Base, carrying four hydrogen bombs. Though the weapons didn’t detonate, the crash scattered radioactive debris — including plutonium-laced components — across miles of Arctic sea ice near North Star Bay.
The U.S. launched an urgent recovery operation, dispatching Air Force and Atomic Energy Commission personnel to the crash site in sub-zero temperatures and near-total darkness. Danish authorities participated in the environmental response but not the weapon recovery.
The incident triggered alarm in Copenhagen. Until then, Denmark had no formal confirmation that nuclear weapons were being flown — let alone stored — in Greenland. The crash forced the issue into the open. Shortly afterwards, Denmark publicly restated its commitment to a nuclear-free policy, this time explicitly applying it to Greenland and its airspace.
The U.S. halted airborne nuclear alert flights immediately. The BMEWS mission continued, but aerial monitoring flights were rerouted from Thule to Alaska by April 1968.
Fallout and Political Reckoning
The political consequences of the crash unfolded slowly but dramatically. In Denmark, the incident ignited long-suppressed public anxieties and spurred parliamentary debates. In the 1990s, following press revelations, the Danish government sought clarification from Washington. In 1995, the U.S. admitted — for the first time — that it had stored and flown nuclear weapons in Greenland during the 1950s and 60s.
These revelations prompted the Danish Institute of International Affairs to launch a formal investigation. Its 1996 report, Grønland under den kolde krig (Greenland During the Cold War), reproduced the original Hansen letter and documented the double standard that had defined Denmark’s nuclear posture.
Even so, large portions of the U.S. record remain classified — including key State Department cables and U.S. Embassy communications. The National Security Archive continues to pursue declassification requests to uncover the full extent of Danish-American nuclear cooperation in Greenland.
Strategic Ice
The story is more than historical intrigue. It speaks to Greenland’s enduring geopolitical significance. In 1946, the Truman administration considered purchasing the island. In 2019, President Donald Trump proposed buying Greenland again, even floating the idea of force. Though widely ridiculed, the proposal underscored Washington’s long-held view of Greenland as a strategic asset — first against the Nazis, then the Soviets, and now amid Arctic competition with China and Russia.
