Operation Castle: Bravo Blast
The Bravo event of the Castle series yielded 15 megatons. This was the largest detonation made by the US. Because of a miscalculation, it was twice as powerful as planned. Bravo was the single worst incident of fallout exposure for any US testing, delivering fallout to more than 7,000 square miles of ocean and islands. Both civilians and military personnel were acutely exposed to radiation levels resulting in injuries to some people.
It left a crater that is visible today in the northwest corner of the atoll.
To see a chart of the larger weapons tested in the Marshall Islands, the Pacific Proving Ground, as it was referred to by the military, click here.
To see declassified video of the blast and the bomb, click here: Blast Movie
The Bravo device was detonated from a firing station located on Enyu Island. Given the proximity of the firing station to ground zero and the surprise yield of the blast, the crew within the bunker were shaken, but well protected from the radiation. Outside the bunker after 1 hour, radiation levels were 250 Rems/hour. Inside: .035Rems/hour. To see what these doses mean, click here.
Within one minute of detonation, the blast wave from the explosion had moved outward from the burst point, stripping the nearby atoll islands of vegetation.
Enyu Island Bunkers as seen in 2001
The detonation created a serious fallout situation. The graphic below (courtesy of atomicarchive.com) shows the extent of the radiation from the blast:
To understand what these levels of radiation mean in terms of health hazards, click here.
The Fukuryu Maru, whose location is shown in the above graphic, was a small Japanese fishing boat. After the Bravo detonation radioactive ash - vaporized coral - fell on the ship. Within hours, the crew members began to experience burning and nausea. Later their skin would darken and some of the crew's hair fell out. One later died from the radiation exposure. As shown above this vessel was exposed to 1,000 rads, well above the threshold where vomiting and severe physical effects are felt.
People on Rongelap were also exposed to significant amounts of radiation and were later evacuated:
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