fission weapon), raising expectations to a near certainty that the concept would work. On November 1, 1952, the Teller–Ulam configuration was tested in the "Ivy Mike" shot at an island in the Enewetak atoll, with a yield of (over 450 times more powerful than the bomb dropped on Nagasaki during World War II). The device, dubbed the Sausage, used an extra-large fission bomb as a "trigger" and liquid deuterium, kept in its liquid state by of cryogenic equipment, as its fusion fuel, and it had a mass of around altogether. An initial press blackout was attempted, but it was soon announced that the US had detonated a megaton-range hydrogen bomb. The elaborate refrigeration plant necessary to keep its fusion fuel in a liquid state meant that the "Ivy Mike" device was too heavy and too complex to be of practical use. The first deployable Teller–Ulam weapon in the US would not be developed until 1954, when the liquid deuterium fuel of the "Ivy Mike" device would be replaced with a dry fuel of lithium deuteride and tested in the "Castle Bravo" shot (the device was codenamed the Shrimp). The dry lithium mixture performed much better than had been expected, and the "Castle Bravo" device that was detonated in 1954 had a yield two-and-a-half times greater than had been expected (at , it was also the most powerful bomb ever detonated by the United States). Because much of the yield came from the final fission stage of its tamper, it generated much nuclear fallout, which caused one of the worst nuclear accidents in US history after unforeseen weather patterns blew it over populated areas of the atoll and Japanese fishermen on board the Daigo Fukuryu Maru. After an initial period focused on making multi-megaton hydrogen bombs, efforts in the United States shifted towards developing miniaturized Teller–Ulam weapons which could outfit Intercontinental Ballistic Missiles and Submarine Launched Ballistic Missiles. The last major design breakthrough in this respect was accomplished by the mid-1970s, when versions of the Teller–Ulam design were created which could fit on the end of a small MIRVed missile. Soviet research In the Soviet Union, the scientists working on their own hydrogen bomb project also ran into difficulties in developing a megaton-range fusion weapon. Because Klaus Fuchs had only been at Los Alamos at a very early stage of the hydrogen bomb design (before the Teller–Ulam configuration had been completed),