On January 21, 1968, a U. S. B-52 Stratofortress carrying four B28FI thermonuclear bombs caught fire over Baffin Bay and crashed onto the sea ice seven miles from Thule Air Base, Greenland.
The conventional explosives in the warheads detonated on impact, pulverizing the weapons, scattering radioactive debris over a wide swath of ice, and melting a huge crater into the frozen sea. Project Crested Ice, the massive cleanup operation, saw American and Danish personnel working in sub-zero dark Arctic conditions to scrape up thousands of tons of contaminated snow, ice, and wreckage. Despite the intense efforts, components of the weapons—including primary fissile cores and thermal radioisotope material—plunged into the ocean depths beneath the shifting ice.
Cold War secrecy masked the full extent of the environmental impact and the lingering radioisotope contamination for decades, creating a geopolitical nightmare between Denmark and the United States over Greenlandic sovereign land.