"Bravo" Both Triumphs and Fails
The U.S. detonated its first deliverable thermonuclear weapon on February 28, 1954, at Bikini. Known as the "Shrimp" device of the "Castle Bravo" test, the U.S.'s new test series, the weapon used lithium deuteride with a 40% content of the lithium-6 isotope as its fusion fuel. The device yielded 15 megatons of energy, over twice its expected yield, and although it was the most powerful explosion in the history of American nuclear testing, it became the worst radiological disaster in U.S. history.
The combination of the unexpectedly large blast and poor weather conditions caused a cloud of radioactive nuclear fallout to contaminate over 7,000 square miles, including Marshall Island natives and the crew of a Japanese fishing boat, as a snow-like mist. The contaminated islands were evacuated (and are still uninhabitable), but the natives received enough of a radioactive dose that they suffered far elevated levels of cancer and birth defects in the years to come. The crew of the Japanese fishing boat, Fifth Lucky Dragon, returned to port suffering from radiation sickness and skin burns. Their cargo, many tons of contaminated fish, managed to enter into the market before the cause of their illness was determined. When a crewmember died from the sickness and the U.S. made public the full results of the contamination, Japanese concerns were re-ignited about the hazards of radiation and resulted in a boycott on eating fish (a main staple of the island country) for some weeks.
Half a world away, the first Soviet two-stage thermonuclear bomb was tested in Kazakhstan on November 22, 1955. The bomb, airdropped from 10,000 feet, yielded 1.6 megatons, and the yield could have been doubled. The fact that the U.S.'s "Bravo" hydrogen bomb test in 1954 had yielded 15 megatons propelled the Soviets to continue research on even more powerful bomb designs.