Although some progress towards detente had been made with the signing in 1963 of the Test Ban Treaty between the USA and the Soviet Union, there were still plenty of itchy fingers around nuclear buttons when, on January 17 1966, during a routine mid-air refueling operation off the Mediterranean coast of southern Spain, a US B-52 bomber collided with a KC-135 tanker aircraft. The B-52 was patrolling the European skies on a typical Cold War sortie when the accident occurred at 9,000 m (30,000 ft). Both planes crashed to the ground outside the fishing village of Palomares in Andalusia, killing the entire tanker crew and three members of the bomber crew; the remaining four crewmen managed to parachute to safety.
What made this mid-air collision no ordinary accident was the fact that the B-52 bomber was carrying a nuclear payload comprising four H-Bombs. Three bombs crashed with the plane; although the hydrogen cores remained intact, the non-nuclear explosives in two of them detonated upon impact, contaminating a wide area of agricultural land with plutonium dust. Although the American authorities played down the significance of the incident, the massive clear-up operation that followed gave ample evidence of how worried they were. Two thousand US servicemen were involved and blanket embargoes were placed on the local tomato crop and fishing industry.
The fourth bomb, which had been jettisoned over the water, was eventually found on the sea-bed after an intensive 80-day search by more than 30 ships. The Palomares incident remains the worst accident ever to have occurred involving American nuclear weapons; the clean-up and subsequent compensation claims are said to have cost the USA over $180 million.
When: January 17 1966
Where: Palomares, Andalucia, Spain
Death toll: Seven US crewmen were killed in the accident. Whilst there were no direct civilian casualties on the ground, the local population are still given annual medical checks to this day.
You should know: As recently as October 2006 the USA and Spain agreed to undertake a further clean-up of radioactive land in the Palomares area.