  nuclear weapons tests are experiments carried out to determine the effectiveness, yield, and explosive capability of nuclear weapons. throughout the 20th century, most nations that developed nuclear weapons tested them. testing nuclear weapons can yield information about how the weapons work, as well as how the weapons behave under various conditions and how personnel, structures, and equipment behave when subjected to nuclear explosions. nuclear testing has often been used as an indicator of scientific and military strength, and many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status by means of a nuclear test. the first nuclear weapon was detonated as a test by the united states at the trinity site on july 16, 1945, with a yield approximately equivalent to 20 kilotons of tnt. the first hydrogen bomb, codenamed "mike", was tested at the enewetak atoll in the marshall islands on november 1, 1952 (local date), also by the united states. the largest nuclear weapon ever tested was the "tsar bomba" of the soviet union at novaya zemlya on october 30, 1961, with the largest yield ever seen (), an estimated 50â58 megatons. in 1963, three (uk, us, soviet union) of the four nuclear states and many non-nuclear states signed the limited test ban treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. the treaty permitted underground nuclear testing. france continued atmospheric testing until 1974, and china continued until 1980. neither has signed the treaty."the treaty has not been signed by france or by the peoples republic of china." u.s. department of state, limited test ban treaty. underground tests in the united states continued until 1992 (its last nuclear test), the soviet union until 1990, the united kingdom until 1991, and both china and france until 1996. in signing the comprehensive test ban treaty in 1996, these states have pledged to discontinue all nuclear testing. however, , the treaty has not yet entered into force because of failure to be signed/ratified by eight specific countries. non-signatories india and pakistan last tested nuclear weapons in 1998. the most recent nuclear test  in february 2013 in north korea. in january 2013, north korea had announced that it planned to conduct further tests involving rockets that can carry satellites as well as nuclear warheads "to strike and attack the united states".{{cite web | url=http://www.usnews.
Nuclear_weapons Nuclear_weapons_testing