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Daigo Fukuryū Maru

Japanese fishing boat

  • 15 min read
  • 6 chapters

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Through Compass

The crew suffered acute radiation syndrome (ARS) for a number of weeks after the Bravo test in March. All recovered from the immediate effects of the American test detonation except for Kuboyama Aikichi, the boat's chief radioman, who died on September 23, 1954, from complications of radiation sickness. Kuboyama is considered the first victim of the hydrogen bomb and of the Castle Bravo test.

Early days and final voyage

Built in March 1947 and launched from Koza, Wakayama, the boat was originally named Dainana Kotoshiro Maru (第七事代丸; Kotoshiro Maru No. 7). It was a bonito boat and moored in Misaki Fishing Harbor, Kanagawa Prefecture. It was later remodeled into a tuna fishing boat. In 1953, it moved to Yaizu Port, Shizuoka Prefecture, with a new name, Daigo Fukuryū Maru, translated as Lucky Dragon No. 5 or the Fifth Lucky Dragon.

The Lucky Dragon No. 5 took five ocean voyages, the last of which began on January 22, 1954, and ended on March 14 of that year. The crew set off to go fishing in the Midway Sea near Midway Atoll, but when they lost most of their trawl nets to the sea, they altered their course southward near the Marshall Islands and encountered fallout from the Castle Bravo nuclear test at Bikini Atoll on March 1.

A map of the varying location of the boat in the days leading up to and after the day of the explosion is available. On March 1, the map depicts the vessel very near to the border of the US Navy issued "danger zone notice" dated October 10, 1953. Following March 1, the vessel charted a practically straight geodesic course back to its home port of Yaizu, passing the same latitude as Wake Island between March 4 and 6 and arriving at Yaizu on March 14.

The source of the map does not state how the map was created, that is, it does not state that the ship's log was consulted in the creation of the map, nor does it provide the navigator's measurements with the compass and sextant of the period. The exact position of the ship on the day of the explosion is therefore uncertain. Contemporary references give a figure of "80 miles (130 km) east of Bikini Atoll" without stating the method by which the distance was computed. According to a 1997 paper by Martha Smith-Norris, the ship was operating "14 miles" outside the 57,000 square mile "Danger Area", and it was not detected by radar or visual spotter planes.

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