Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of Operation Castle. Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. They were the first nuclear weapon tests since Trinity in July 1945, and the first detonations of nuclear devices since the atomic bombing of Nagasaki on August 9, 1945. The purpose of the tests was to investigate the effect of nuclear weapons on warships. They were conducted by Joint Army/Navy Task Force One, headed by Vice Admiral William H. P. Blandy rather than by the Manhattan Project, which had developed nuclear weapons during World War II. The first test was Able. The bomb was named Gilda after Rita Hayworth's character in the 1946 film Gilda, and was dropped from the B-29 Superfortress Dave's Dream of the 509th Bombardment Group on July 1, 1946.