Against the backdrop of the cold war, American and Soviet scientists engaged in a dangerous race to see who could build and detonate the world's largest bomb. On March 1, 1954, the U.S. conducted the "Castle Bravo" hydrogen bomb test. It unleashed a fifteen megaton explosion that vaporized three entire coral islands and sent ash 100,000 feet in the air. After the disaster, the U.S. refocused its efforts on smaller, more precise bombs. The Soviet Union, however, continued to build massive devices capable of destroying entire cities. On October 30, 1961, the Soviet bomb program reached its zenith above the north European island of Novaya Zemlya. When the 50-megaton "Tsar" was detonated, sending a blast wave three times around the world, it made "Castle Bravo" look insignificant.