A B-52 bomber crashes near Thule Air Base, contaminating the area after its nuclear payload ruptures. One of the four bombs remains unaccounted for after the cleanup operation is complete.

The Boeing B-52 Stratofortress is an American long-range subsonic jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the United States Air Force (USAF) since 1955 and was flown by NASA from 1959 to 2007. The bomber can carry up to 70,000 pounds (32,000 kg) of weapons and has a typical combat range of around 8,800 miles (14,200 km) without aerial refueling.

On 21 January 1968, an aircraft accident, sometimes known as the Thule affair or Thule accident, involving a United States Air Force (USAF) B-52 bomber occurred near Thule Air Base in the Danish territory of Greenland. The aircraft was carrying four B28FI thermonuclear bombs on a Cold War "Chrome Dome" alert mission over Baffin Bay when a cabin fire forced the crew to abandon the aircraft before they could carry out an emergency landing at Thule Air Base. Six crew members ejected safely, but one who did not have an ejection seat was killed while trying to bail out. The bomber crashed onto sea ice in North Star Bay, Greenland, causing the conventional explosives aboard to detonate and the nuclear payload to rupture and disperse, resulting in radioactive contamination of the area.

Pituffik Space Base, formerly Thule Air Base, is a United States Space Force base located on the northwest coast of Greenland in the Kingdom of Denmark under a defense agreement between Denmark and the United States. 150 United States guardians serve there, after the United States significantly reduced its presence from 6000 personnel during the Cold War. Denmark was a founding member of NATO in 1949, and the 1951 Greenland Defense Agreement allowed the United States to operate the base under a NATO framework, as long as both Denmark and the United States remain NATO members. Under the agreement, the Danish national flag must be flown at the base to recognize that the base is on Danish territory, but the United States is allowed to fly its own flag alongside the Danish flag on the facilities it operates.