In 1971, on which island was the largest underground test of nuclear weapons ever conducted by the USA?

Question

Which island purchased by USA from Denmark in 1917 and why US need to purchase it?
Please share the details of transaction?

Answer 1

Amchitka
There were nuclear weapons tests at all of these: Christmas Island (by the British) 1957/58; Bikini Atoll (by the USA) 1946-58 but none in-ground; Mururoa Atoll (by the French) 1966 to 1996. The 1971 test, codenamed Cannikin, on Amchitka in Alaska was 250 times the yield of the bomb that was dropped on Nagasaki.