During the height of the Cold War, the United States Strategic Air Command maintained Operation Chrome Dome, keeping nuclear-armed B-52 bombers constantly airborne near the Soviet border. On January 21, 1968, a fire broke out in the navigator cabin of a B-52G flying over Baffin Bay. The crew was forced to abandon the aircraft, which crashed onto the sea ice of North Star Bay near Thule Air Base, Greenland.
The conventional explosives inside the four B-52 nuclear bombs detonated upon impact, spreading radioactive material over a vast area of ice. A massive Joint US-Danish cleanup effort, codenamed Project Crested Ice, worked under polar darkness and extreme cold to scrape up thousands of tons of contaminated snow, ice, and debris. However, classified documents declassified decades later revealed that not all weapon components were recovered.
Secondary bomb casing analysis and seabed searches suggested that the primary fusion stage or active core of weapon number four sank beneath the seabed through the melted ice. Despite extensive submarine search missions, the missing piece of nuclear history remains somewhere on the ocean floor in the frigid Arctic depths.