LINEAR VS THRESHOLD: THE GREAT DEBATE On July 2, 1958 an American-owned, Hiroshima-built yacht sailed into the test zone near Bikini Atoll in the Marshall Islands District. On it were Dr. Earle Reynolds, his wife and children, and a Japanese citizen born in Hiroshima. About 12 hours after entering the latitude and longitude of the zone, the Phoenix was bounded by the U.S. Coast Guard and ordered to Kwajalein. Their entry into the zone was inten- tional, the result of a moral decision to protest the testing by the United States of nuclear weapons. The adventure of this sole sailboat in the waters of the Marshall Islands was representative of a great worldwide concern by many people at that time with the effects of radioactive fallout on man as a result of nuclear testing. The world's first "superbomb" perhaps better known as a thermonuclear or H-(Hydrogen) bomb was detonated by the United States on Fugelab Island of Eniwetok Atoll on October 31, 1952 at 1915 (GCT). A little over one year later, the Union of Soviet Socialist Republics detonated its first H-bomb device on December 12, 1953. The United Kingdom followed with its first H-bomb explosion on May 15, 1957 (ENW). The international anxiety which developed over the effects of these tests and their fallout was due to the fact, discussed earlier, that thermonuclear explosions in the megaton range reached heights of 90,000 feet or more. A-bomb explosions normally left their fallout in the troposphere which soon returned to earth. H-bomb detonations, however had begun to "load" the stratosphere with fallout that would disperse all over the world and only gradually fall out over a period of months or years. 35