Nuclear weapons testing is the act of experimentally and deliberately firing one or more nuclear devices in a controlled manner pursuant to a military, scientific or technological goal. This has been done on test sites on land or waters owned, controlled or leased from the owners by one of the eight nuclear nations: the United States, the Soviet Union, the United Kingdom, France, China, India, Pakistan and North Korea, or has been done on or over ocean sites far from territorial waters. There have been 2,121 tests done since the first in July 1945, involving 2,476 nuclear devices. As of 1993, worldwide, 520 atmospheric nuclear explosions (including eight underwater) have been conducted with a total yield of 545 megatons (Mt): 217Â Mt from pure fission and 328Â Mt from bombs using fusion, while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 is 1,352 explosions with a total yield of 90Â Mt. As a result of the 1996 Comprehensive Nuclear-Test-Ban Treaty, there were no declared tests between the 1998 Pakistani Chagai-II and the 2006 North Korean test, and none outside North Korea to date.
Very few unknown tests are suspected at this time, the Vela incident being the most prominent. Israel is the only country suspected of having nuclear weapons but not confirmed to have ever tested any.