Nuclear weapons testing: The Romeo shot of Operation Castle is detonated at Bikini Atoll. Yield: 11 megatons.

Nuclear weapons tests are experiments carried out to determine the performance of nuclear weapons and the effects of their explosion. Over 2,000 nuclear weapons tests have been carried out since 1945. Nuclear testing is a sensitive political issue. Governments have often performed tests to signal strength. Because of their destruction and fallout, testing has seen opposition by civilians as well as governments, with international bans having been agreed on. Thousands of tests have been performed, with most in the second half of the 20th century.

Castle Romeo was the code name given to one of the tests in the Operation Castle series of U.S. nuclear tests. It was the first test of the TX-17 thermonuclear weapon, the first deployed thermonuclear bomb.

Operation Castle was a United States series of high-yield (high-energy) nuclear tests by Joint Task Force 7 (JTF-7) at Bikini Atoll beginning in March 1954. It followed Operation Upshot–Knothole and preceded Operation Teapot.

Bikini Atoll, known as Eschscholtz Atoll between the 19th century and 1946, is a coral reef in the Marshall Islands consisting of 23 islands surrounding a 229.4-square-mile (594.1 km²) central lagoon. The atoll is at the northern end of the Ralik Chain, approximately 530 miles (850 km) northwest of the capital Majuro.