Cannikin

Cannikin was an underground nuclear weapons test performed on November 6, 1971, on Amchitka island, Alaska, by the United States Atomic Energy Commission. The experiment, part of the Operation Grommet nuclear test series, tested the unique W71 warhead design for the LIM-49 Spartan anti-ballistic missile. With an explosive yield of almost 5 megatons of TNT (21 PJ), the test was the largest underground explosion ever detonated by the United States.

Prior to the main five-megaton test in 1971, a 1 Mt (4.2 PJ) test took place on the island on October 2, 1969, for calibration purposes, and to ensure the subsequent Cannikin test could be contained. This test, Milrow, was included in the Operation Mandrel nuclear test series.

The Cannikin test faced considerable opposition on environmental grounds. The campaigning environmental organization Greenpeace grew out of efforts to oppose the test.