From 1941 until 1945, the United States established numerous and extensive facilities for air and sea traffic in Greenland, as well as radio beacons, radio stations, weather stations, ports, depots, artillery posts, and search-and-rescue stations. The United States Coast Guard also provided a considerable portion of the civilian resupply task up and down both coasts.

The fall of Denmark in April 1940 left the Danish colony of Greenland an unoccupied territory of an occupied nation, under threat of seizure by the United Kingdom or Canada . To forestall this, the United States acted to guarantee Greenland's position. However, with the entrance of the United States into the war in December 1941, Greenland became a combatant.

Before the war, Greenland was a tightly controlled colony of Denmark, otherwise closed off to the world. After the invasion of Denmark on 9 April 1940, Greenland was left on its own, because the Royal Navy seized any ships arriving from Axis-controlled Europe. The United Kingdom and Canada initially laid plans to occupy points of interest on the island, but the United States, still neutral, firmly rejected "third party" intervention there. The sheriffs ("landsfogeder") of South and North Greenland, Eske Brun and Aksel Svane, invoking the emergency clause of a 1925 law specifying how Greenland was ruled, declared Greenland a self-ruling territory, believing this to be in the best interests of the colony as Denmark was occupied by Germany. This step was taken in coordination with the Danish ambassador to the United States, Henrik Kauffmann, and the US State Department, and comported with the American declaration of 1920 that no third nation would necessarily be accepted as a sovereign in Greenland. This diplomatic stance was seen as an extension of the Monroe Doctrine.[1]

Although the Danish government continued in power and still considered itself neutral, it was forced to obey German wishes in foreign policy matters. Kauffmann immediately recognized that his government was unable to exercise its full sovereignty, and therefore began to act in an independent capacity. On 13 April he took counsel with the Greenland sheriffs, and after some controversy they agreed to recognize him as their representative in the United States. Since the United States would not offer diplomatic recognition and aid to Greenland unless the local administration was independent, the sheriffs informed the local advisory parliament ("Landsraad") on 3 May that "there was no choice" but to act as a sovereign nation. The Danish Government continued to send orders to the colony via radio and through Portugal, but these messages were ignored.[2] In this decision they were influenced by their determination to avoid becoming subject to a Canadian occupation and thus being drawn into the war.[1]

The Greenlanders were also aware of the heavy Norwegian presence in Canada. In the event that Canada attempted to occupy the colony, they were worried that Free Norwegian Forces would be stationed in the area.[3] This was a cause for concern, as the Norwegians had been vying for control over part of the territory until the Permanent Court of International Justice settled the dispute in 1933.[4] Instead, they requested the protection of the United States, whose Treasury Department agreed to dispatch the US Coast Guard vessels, USCGC Comanche and USCGC Campbell with supplies and a consular team to establish a provisional consulate at Godthaab. Accepting the protection of the Americans, a third party, was seen as less of a threat to Greenland's sovereignty.[3] Comanche arrived at Ivigtut on 20 May, and Godthaab on 22 May, thereby establishing direct diplomatic relations with Greenland.[1] Canada sent a consul and vice-consul to Godthaab two weeks later.

The Ivigtut cryolite mine in southwestern Greenland, 1940

In 1940, the chief concern of all interested parties was to secure the strategically important supply of cryolite from the mine at Ivigtut. Cryolite was a key component used in the production of aluminum. Due to diplomatic considerations, no American soldiers could be used to protect the mines so the US State Department recruited fifteen Coast Guardsmen who were voluntarily discharged and in turn hired by the mine as guards. Three-inch naval deck guns were supplied by Campbell and the recently arrived USCGC Northland along with eight machine guns, fifty rifles, and thousands of rounds of ammunition.[5] In this way the United States maintained neutrality and still preempted British-Canadian plans for the island.

The Dane, Eske Brun, decided that Greenland should undertake its own measures to ensure its sovereignty. He made an appeal to the Greenland's guides and hunters to join an elite unit tasked with patrolling the most remote areas of the colony.[3] Using the rifles left by the Americans, he directed the creation of what became the Sirius Sledge Patrol. The 15 man volunteer team was made up of native Inuit, Danish colonists, and Norwegian expatriates.[6]

Germany made no attempts to reach Greenland in 1940. However, three Norwegian vessels reached Norwegian stations on the East Coast. Two were intercepted by the Royal Navy, one (which was left to go) by the US Coast Guard. Britain violated Greenland neutrality by destroying the Norwegian stations, drawing an American protest, and a German reconnaissance plane made a flight over the East Coast in November in order to check on a Norwegian station that had not been heard from.

In 1941, the situation shifted towards delivery of Lend-Lease aircraft to Britain via the North Atlantic island "stepping stones." Again, the United Kingdom and Canada pressed for an operation to establish an airfield near Cape Farewell. This forced the United States and the Greenland government to formalize an American protectorate in order to preserve the island's neutrality. Following surveys in 1940 and 1941, two locations for air bases were located, and a naval base established close to Ivigtut. The American bases and stations were codenamed under the Bluie West and Bluie East moniker.

President Franklin D. Roosevelt took a strong personal interest in Greenland's fate. On 9 April 1941, the anniversary of the German occupation, the Danish envoy Kauffmann, against the instructions of his government, signed an executive agreement with Secretary of State Cordell Hull, allowing the presence of American troops and making Greenland a de facto United States protectorate. The cryolite mine in Ivigtut was a unique asset that made it possible for Greenland to manage fairly well economically during the war. The United States supplied the island and sent patrol boats to survey the east coast of Greenland although this activity was limited by seasonal ice. The Coast Guard, in coordination with Eske Brun, created the Northeast Greenland Sledge Patrol, consisting of 15 men, many of them former hunters in the area. Their task was to patrol the coast to discover any German activity. However, in 1941 there was no such landing, although the Norwegian resupply trawler Buskø was encountered in September. Among its otherwise innocuous crew and passengers was a civilian Norwegian who intended to provide weather reports for German contacts in Norway. This ship was seized and brought to Boston.

In 1941, British ships continued to interfere with weather stations on the east coast. A couple of reconnaissance aircraft from Norway flew over Scoresbysund.