In 1949, Denmark joined NATO (North Atlantic Treaty Organization) and abandoned its attempt to remove the United States bases. By the outbreak of the Korean War next year, the USAF embarked on a global program of base-building in which Thule (at the time) would be considered the crown jewel owing to its location across the Pole from the USSR, as well as its merit of being the northernmost port to be reliably resupplied by ship. Thule became a key point in American nuclear retaliation strategy. Strategic Air Command (SAC) bombers flying over the Arctic presented less risk of early warning than using bases in the United Kingdom. Defensively, Thule could serve as a base for intercepting bomber attacks along the northeastern approaches to Canada and the US. A board of Air Force officers headed by Gordon P. Saville made a recommendation to pursue a base at Thule in November 1950. It was subsequently supported by the Joint Chiefs of Staff and approved by President Truman. To replace the agreement entered into during World War II between the US and Denmark, a new agreement with respect to Greenland was ratified on 27 April 1951 (effective on 8 June 1951). At the request of NATO, the agreement became a part of the NATO defense program. The pact specified that the two nations would arrange for the use of facilities in Greenland by NATO forces in defense of the NATO area known as the Greenland Defense Area. Thule AB was constructed in secret under the code name Operation Blue Jay, but the project was made public in September 1952. Construction for Thule AB began in 1951 and was completed in 1953. The construction of Thule is said to have been comparable in scale to the enormous effort required to build the Panama Canal. The United States Navy transported the bulk of men, supplies, and equipment from the naval shipyards in Norfolk, Virginia. On 6 June 1951 an armada of 120 ships sailed from Naval Station Norfolk. On board were 12,000 men and 300,000 tons of cargo. They arrived at Thule on 9 July 1951. Construction, aided by continuous daylight in summer, took place around the clock. The workers lived on board the ships until quarters were built. Once they moved into the quarters, the ships returned home. On 16 June 1951, the base was accidentally discovered by French cultural anthropologist and geographer Jean