17th January 1966 - 'Broken Arrow'

On 17th January 1966 an American tanker plane and a B-52 bomber carrying four 1 Megaton hydrogen bombs crashed while refuelling in the air over the Spanish Mediterranean coast.
Pieces of wreckage and three of the bombs fell near the town of Palomares. The fourth bomb fell in the Mediterranean and was later found intact as too one of the bombs near Palomares.
The other two exploded in the fall and their content of fissile material was scattered over an area of about 2.3 km2 consisting of agricultural land, urban land and uncultivated land. No one was injured in the accident but a large area used for cultivating tomatoes had to be decontaminated.
About 1000 m³ of radioactively contaminated material was later removed for storage in the USA.

Related links:

Broken Arrow (Atomic Museum)

The Palomares "Broken Arrow," January 1966 (Brookings Institution)

Palomares, Spain Medical Surveillance and Environmental Monitoring (U.S. Department of Energy - Office of Health Programs)

Air Force Releases Reports on Palomares, Spain and Thule Airbase, Greenland Nuclear Weapons Accidents