The military uses the term “broken arrow” to describe any incident in which a nuclear weapon is lost, stolen or inadvertently detonated. That might seem like a rare phenomenon, but records show that the United States has experienced more than 30 such close calls since the beginning of the nuclear age. Risks were particularly high during the Cold War, when bombers armed with thermonuclear weapons patrolled the skies around the clock. With so many planes in the air, a few experienced mishaps that led to crashes and unplanned bomb drops. In 1957, a 42,000-pound hydrogen bomb accidentally fell through the bomb bay doors of a B-36 bomber as it flew over New Mexico. The bomb’s non-nuclear conventional explosives detonated upon impact, killing a grazing cow and leaving behind a crater 12 feet deep. Luckily, the nuclear payload did not blow. Another famous near-disaster came in 1961, when a B-52 bomber suffered a fuel leak and exploded over Goldsboro, North Carolina. The plane broke apart and released two Mark 39 hydrogen bombs. All that prevented one of them from detonating was a single low-voltage safety switch.
Similar fail-safe measures have ensured that no broken arrow has ever resulted in a nuclear blast, but there have been a few incidents in which a weapon was lost and never found. During the Vietnam War, a plane carrying a nuclear bomb slid off the aircraft carrier Ticonderoga and disappeared in the Pacific. In 1968, the submarine Scorpion mysteriously sank with all 99 hands—and two nuclear-tipped torpedoes—off the coast of the Azores. The Soviet Union experienced a similar disaster two years later, when the nuclear submarine K-8 went down in the Bay of Biscay. All told, the combined broken arrows of the United States and Russia have left several dozen nuclear warheads lost at sea.