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The United States and Greenland, Part I: Episodes in Nuclear History 1947-1968

Greenland “Green Light”: Danish PM’s Secret Acquiescence Encouraged U.S. Nuclear Deployments

Pentagon Approved Nuclear-Armed B-52 Flights Over Greenland

 National Security Archive | June 3, 2025 

The Trump administration’s intention to acquire Greenland, including possibly by force, has put a focus on the history of its strategic interest to U.S. policymakers. Today, the National Security Archive publishes the first of a two-part declassified document collection on the U.S. role in Greenland during the middle years of the Cold War, covering the decisions that led to the secret deployment of U.S. nuclear weapons in the Danish territory in 1958 to the 1968 crash of a nuclear-armed B-52 bomber near Thule Air Base that left plutonium-laced debris scattered across miles of Arctic sea ice.[1]

The radioactive mess caused by the accident required a major clean-up and caused a serious controversy in U.S.-Denmark relations. The U.S. had never officially told Denmark that it was flying nuclear weapons over Greenland, although Danish officials suspected it; nor had the U.S. informed the Danes that it had once stored nuclear weapons in Greenland, although in 1957 they had received a tacit “green light” to do so from the Danish prime minister, according to documents included in today’s posting. But both the nuclear-armed overflights of Greenland and the storage of nuclear weapons there were in strong contradiction to Denmark’s declared non-nuclear policy. When the bomber crash exposed the overflights, Denmark tried to resolve the conflict by seeking a U.S. pledge that Greenland would be nuclear free.

This new publication revisits the nuclear and strategic history of the United States and Greenland as it emerged during the late 1940s through the crash in 1968, highlighting key declassified documents from the archival record, FOIA releases, the Digital National Security Archive (DNSA), and other sources. The analysis draws on the work of U.S. and Danish scholars who have written about the B-52 crash and the history of the U.S., Denmark, and Greenland during the Cold War, including revelations in the 1990s that prompted Danish experts to revisit the historical record.[2]

Part I, below, looks at U.S. strategic interests in Greenland in the early Cold War period, including Danish government acquiescence to the storage of nuclear weapons there, U.S. nuclear-armed airborne alert flights over Greenland, and the 1968 B-52 crash. Part II will document the aftermath of the accident, including the clean-up of contaminated ice, the U.S.-Denmark government nuclear policy settlement, and the failed search for lost nuclear weapons parts deep in the waters of North Star Bay.

Background

Greenland has been seen as an important strategic interest to United States defense officials and policymakers since World War II. After the fall of France in June 1940, the Nazis seized Denmark, and the Roosevelt administration feared that Germany would occupy Greenland, threatening Canada and the United States. In response, the U.S. insisted that Greenland was part of the Western Hemisphere and thus a territory that had to be “assimilated to the general hemispheric system of continental defense.” The U.S. began talks with Danish Ambassador Henrik Kauffmann, who was acting on his own authority as “leader of the Free Danes” and in defiance of the German occupiers. On 9 April 1941, Kauffmann signed an extraordinary agreement with Washington giving the United States almost unlimited access to build military facilities in Greenland and would remain valid as long as there were “dangers to the American continent,” after which the two parties could modify or terminate it. By the end of World War II, the U.S. had 17 military facilities in Greenland. After the liberation of Denmark from German rule, the Danish Parliament ratified the Kauffmann-U.S. agreement on 23 May 1945, but it assumed its early termination, with Denmark taking over Greenland’s defense.[3]

In 1946, the Truman administration gave brief consideration to buying Greenland because it continued to see it as important for U.S. security.[4] During 1947, with the U.S. beginning to define the Soviet Union as an adversary, defense officials saw Greenland as an important “primary base,” especially because they were unsure about long-term access to Iceland and the Azores.[5] Thus, maintaining U.S. access was an important concern, as exemplified in an early National Security Council report that U.S. bases in Greenland, along with Iceland and the Azores, were of “extreme importance” for any war “in the next 15 or 20 years.” For their part, Danish authorities had no interest in selling Greenland but sought to restore their nation’s sovereignty there; having joined NATO, they dropped their traditional neutrality approach and were more willing to accept a limited U.S. presence. In late 1949, the U.S. and Denmark opened what became drawn out negotiations over Greenland; during 1950, the U.S. even returned some facilities to Denmark, including Sandrestrom air base. But in late 1950, with Cold War tensions deepening, the Pentagon gave the negotiations greater priority, seeking an agreement that would let the U.S. develop a base at Thule as part of an air strategy designed to reach Soviet targets across the Arctic.[6]

In April 1951, the two countries reached an agreement on the “defense of Greenland” that superseded the 1941 treaty, confirmed Danish sovereignty, and delineated three “defense areas” for use by the United States, with additional areas subject to future negotiations. Under the agreement, each signatory would “take such measures as are necessary or appropriate to carry out expeditiously their respective and joint responsibilities in Greenland, in accordance with NATO plans.” Consistent with that broad guidance, the U.S. would be free to operate its bases as it saw fit, including the movement of “supplies,” and with no restrictions on its access to airspace over Greenland. With this agreement, Washington had achieved its overriding security goals in Greenland. To move the agreement through Parliament, the Danish government emphasized its defensive character, although the negotiators and top officials understood that U.S. objectives went beyond that.[7]

In 1955, a few years after the 1951 agreement, the Joint Chiefs of Staff tried to revive interest in purchasing Greenland to ensure U.S. control over the strategically important territory and without having to rely on an agreement with another government. But the JCS proposal never found traction in high levels of the Eisenhower administration. The State Department saw no point to it, since the United States was already “permitted to do almost anything, literally, that we want to in Greenland.” The 1951 agreement stayed in place for decades. Denmark and the United States finally modified it in 2004, limiting the “defense area” to Thule Air Base and taking “Greenland Home Rule” more fully into account.

Nuclear Issues

When the U.S. negotiated the 1951 agreement, nuclear deployments were not an active consideration in official thinking about a role for U.S. bases for Greenland. Yet by 1957, when U.S. government agencies, including the State Department, became interested in deploying nuclear bombs at Thule, they used the agreement’s open-ended language to justify such actions. According to an August 1957 letter signed by Deputy Under Secretary of State Robert Murphy, the Agreement was “sufficiently broad to permit the use of facilities in Greenland for the introduction and storage of [nuclear] weapons.” The problem was to determine whether Danish leaders would see it that way.

While Defense Department officials were willing to go ahead on the deployments without consulting the Danish Government, Murphy thought it best to seek the advice of the U.S. ambassador, former Nebraska Governor Val Peterson. Peterson recommended bringing the question to Danish authorities and, having received the Department’s approval, in mid-November 1957 he asked Prime Minister Hans Christian Hansen if he wished to be informed about nuclear deployments. By way of reply, Hansen handed Peterson a “vague and indefinite” paper that U.S. and Danish officials interpreted as a virtual “green light” for the deployments. Hansen raised no objections, asked for no information, and tacitly accepted the U.S. government’s loose interpretation of the 1951 agreement. He insisted, however, that the U.S. treat his response as secret because he recognized how dangerous it was for domestic politics, where anti-nuclear sentiment was strong, and for Denmark’s relations with the Soviet Union, which would have strongly objected.[8]

When Prime Minister Hansen tacitly approved the deployment of U.S. nuclear weapons in Greenland, he was initiating what Danish scholar Thorsten Borring Olesen has characterized as a “double standard” nuclear policy. On the one hand, in a May 1957 address, Hansen had stated that the government would not receive nuclear weapons “under the present conditions.” Thus, Denmark abstained from NATO nuclear storage and sharing plans as they developed in the following years. On the other hand, the Danish leadership treated Greenland differently with respect to nuclear weapons even though, as of 1953, it was no longer a colony but a county represented in Parliament. This double standard was not necessarily a preference for Denmark’s leaders but they felt constrained by the need to accommodate U.S. policy goals in Greenland. Thus, by keeping their Greenland policy secret, Hansen and his successors kept relations with Washington on an even keel while avoiding domestic political crises and pressure from the Soviet Union.[9]

In 1958, the Strategic Air Command deployed nuclear weapons in Greenland, the details of which were disclosed in a declassified SAC history requested by Hans Kristensen, then with the Nautilus Institute. According to Kristensen’s research and the Danish study of “Greenland During the Cold War,” during 1958 the U.S. deployed four nuclear weapons in Greenland—two Mark 6 atomic bombs and two MK 36 thermonuclear bombs as well as 15 non-nuclear components. That SAC kept bombs there for less than a year suggests that it did not have a clear reason to continue storing them in Greenland. Nevertheless, the U.S. kept nuclear air defense weapons at Thule: 48 nuclear weapons were available for Nike-Hercules air missiles through mid-1965. There may also have been a deployment of nuclear weapons for Falcon air-to-air missiles through 1965, but their numbers are unknown.[10]

Airborne Alert and the January 1968 Crash

If it had only been an issue of the U.S. storing nuclear weapons on the ground in Greenland for a few years, the matter might have been kept under wraps for years. But the crash of a U.S. Air Force B-52 on 21 January 1968 near Thule Air Base exposed another nuclear secret and caused serious difficulties in U.S.-Denmark relations. While the bomber crash was quickly overshadowed by North Korea’s seizure of the U.S.S. Pueblo the next day and the Tet offensive that began on 30 January, the coincidence of the three events was a major crisis for the overextended U.S.[11]

Beginning in 1961, accident-prone B-52s were routinely flying over Thule because Greenland had become even more salient to U.S. national security policy. To warn the U.S. of incoming bombers, the Air Force had deployed Distant Early Warning Line radar stations across Alaska and northern Canada during the 1950s and extended them to Greenland in 1960-1961. The Air Force also deployed the Ballistic Missile Early Warning System (BMEWS), with a site located near Thule Air Base in 1960. With BMEWS, the U.S. would receive 15 minutes of warning of a ballistic missile launch.

The warning time was important for U.S. Strategic Air Command (SAC) because it provided the opportunity to launch ground alert bomber forces in the event of an attack. But the possibility of an ICBM strike on U.S. airbases also helped inspire the emergence of airborne alert, whereby SAC kept nuclear-armed B-52s in the air 24 hours a day, ready to move on Soviet targets in the event of war. SAC began to test airborne alert in the late 1950s, and the flights soon became routine. By 1961, SAC had initiated “Chrome Dome,” with 12 B-52s flying two major routes, a Northern Route over North America and a Southern Route across the Atlantic. While SAC leaders used strategic arguments to justify airborne alert, they also had a parochial interest because it kept bombers in the air, giving pilots even more training.[12]

Airborne alert converged with Greenland in August 1961, when SAC and the Joint Chiefs of Staff approved a plan for two B-52 sorties a day to fly over the BMEWS site at Thule. Given the major importance of the BMEWS site, if the Soviets knocked it out in a surprise attack, they could disrupt U.S. early warning capabilities. Thus, SAC insisted on visual observation so that the B-52 crew could check whether the site was intact in the event there were failures in the communications links between Thule and the North American Air Defense Command in Colorado. SAC’s BMEWS Monitor was a routine operation for years, even after the B-52 crash in Palomares, Spain, led to decisions to scale back on airborne alert. Secretary of Defense Robert McNamara wanted to end the program altogether but accepted a JCS compromise proposal for fewer sorties.

Danish military personnel and others nearby were aware of the daily B-52 flights. Moreover, every year there were emergency landings by U.S. bombers, with three in 1967 alone. After a nuclear-loaded B-52 crashed in western Maryland in January 1964, Eske Brun, Denmark’s Under Secretary for Greenland, wondered whether the B-52s flying over Thule carried nuclear weapons and asked U.S. Ambassador William McCormick Blair about the possibility of an accident. Blair suggested that such an “unfortunate” occurrence would be the price of defending the “free world” and that the flights were consistent with the 1951 agreement. The Danes held internal discussions about whether there were any restrictions on U.S. flights over Greenland and decided not to pursue the matter.

According to Scott Sagan, the January 1968 crash was a “normal accident waiting to happen.” The heating system failed on a bomber carrying four nuclear weapons over Thule, causing foam rubber cushions placed under the seats to catch fire. The crew could not extinguish the flames and bailed out after determining that an emergency landing was impossible, with all but one of the seven crew members surviving. While the nuclear weapons carried on the plane did not detonate when the B-52 crashed on Wolstenholme Fjord, near North Star Bay, conventional high explosives carried in the bombs did, causing plutonium contaminated aircraft parts and bomb debris to scatter about the ice for miles.[13]

To recover what they could of the bombs and assess the contamination, SAC sent an emergency team to Thule, including officials from the Atomic Energy Commission (AEC). All of this occurred under incredibly difficult conditions, sub-zero temperatures, and winter arctic darkness. Danish officials joined in the effort, although they would not take part in the bomb-salvaging activity. While SAC’s disaster team discovered most of the bomb parts after the accident, it could not find some of the important pieces, which eventually necessitated an underwater search. An equally significant problem was the possible risk to the local ecology from plutonium contamination, including its impact on Inuit hunters. U.S. officials had to find a way to clean up the icy mess quickly and in a way that was satisfactory to Danish authorities.

Immediately after the accident, JCS Chair Earle Wheeler and Secretary of Defense Robert McNamara ordered nuclear-armed airborne alert flights to end. SAC would continue the BMEWS Monitor using KC-135 tanker aircraft, but that ended that April 1968 when the flights were switched to the BMEWS site in Clear, Alaska. BMEWS, including the site at Thule, remained a U.S. strategic asset until 2001, when the Air Force replaced it with the Solid State Phase Array Radar System.

Soon after the accident, the Danish Foreign Ministry issued a statement that included this language: “Danish policy regarding nuclear weapons also applies to Greenland and also to air space over Greenland. There are no nuclear weapons in Greenland.” With this statement, the Government of Denmark was beginning to abandon the “double standard” by moving toward a consistent no nuclear policy. How Danish authorities worked with Washington to confirm this policy goal will be the subject of Part II.

The crash of the B-52 was no secret in Denmark, but the fact that airborne alert flights over Greenland were routine during the 1960s did not reach public attention until the early 1990s. Prompted by the revelations, the Danish Government asked the U.S. government for more information, which led the State Department to disclose to the Danish government in July 1995 that the U.S. had deployed nuclear bombs and air defense weapons in Greenland during 1958-1965. The State Department letter was secret, but its contents began to leak. The preceding month, the Danish government had released information on the Hansen paper, creating a political scandal and prompting calls for an investigation of the historical record.

The Danish Institute of International Affairs sponsored the research and published its report in 1996, Grønland under den kolde krig: Dansk og amerikansk sikkerhedspolitik 1945–1968 [Greenland During the Cold War: Danish and American Security Policy 1945-1968 ]. The report, which included a full reproduction of the Hansen paper, among other revelations, disclosed much of this once-hidden history.[14] Nevertheless, significant State Department and U.S. Embassy records remain classified and have been the subject of declassification requests by National Security Archive to the U.S. National Archives.

June 4, 2025 Posted by aletho | Deception, Militarism | Denmark, Greenland, NATO, United States | 1 Comment