17th January 1966 an American plane crashed near the Spanish village of Palomares. What was the valuable cargo?

The 1966 Palomares B-52 crash, or the Palomares incident, occurred when a B-52G bomber of the United States Air Force's Strategic Air Command collided with a KC-135 tanker during mid-air refuelling at 31,000 feet (9,450 m) over the Mediterranean Sea. Of the four Mk28-type hydrogen bombs the B-52G carried, three were found on land, and one in the sea. The non-nuclear explosives in two of the weapons detonated upon impact with the ground, resulting in the contamination of a 2-square-kilometer (490-acre) area by plutonium.