TIL that 50 yrs ago today, the US conducted its largest underground nuclear test. A W71 warhead was detonated in a 7-ft-wide, 5,873-ft-deep shaft beneath Amchitka Island, Alaska. The yield was about 5 Megatons. The explosion raised the ground 25 ft, later collapsing into a 1-mile-wide, 60-ft crater.