A “Broken Arrow” is defined as an unexpected event involving nuclear weapons that results in the accidental launching, firing, detonating, theft or loss of the weapon.
A B-52 bomber carrying four nuclear weapons crashed on sea ice after a cabin fire, near Thule Air Base in Greenland. Non-nuclear high explosive material inside the bombs exploded, leading to approximately 6700 cubic meters of ice being contaminated and later removed.
Further materials:
https://www.atomicarchive.com/almanac/broken-arrows/index.html#1960
