Mark 21 nuclear bomb
The Mark 21 nuclear bomb was a United States nuclear gravity bomb first produced in 1955. It was based on the TX-21 "Shrimp" prototype that had been detonated during the Castle Bravo test in March 1954. While most of the Operation Castle tests were intended to evaluate weapons intended for immediate stockpile, or which were already available for use as part of the Emergency Capability Program, Castle Bravo was intended to test a design which would drastically reduce the size and costs of the first generation of air-droppable atomic weapons (the Mk 14, Mk 17 & Mk 24). At long, in diameter, and weighing , the Mk-21 was half the length and one-third the weight of the Mk-17/24 weapons it replaced. Its minimum yield was specified at four megatons.
Daigo Fukuryū Maru
The "Daigo Fukuryū Maru" encountered the fallout from the U.S. Castle Bravo nuclear test at Bikini Atoll, near the Marshall Islands, on March 1, 1954. When the test was held, the "Daigo Fukuryū Maru" was catching fish outside the danger zone that the U.S. government had declared in advance. However, the test was more than twice as powerful as predicted, and changes in weather patterns blew nuclear fallout, in the form of a fine ash, outside the danger zone. On that day, the sky in the west lit up like a sunset. Seven minutes later, the sound of the explosion arrived, with fallout reaching the ship two hours later. The fishermen attempted to escape from the area, but they took time to retrieve fishing gear from the sea, exposing themselves to radioactive fallout for several hours.