That would be this thermonuclear test:
Stephen SchwartzAt this moment in 1954 at Bikini Atoll (6:45 AM March 1, local time), the US conducted its largest H-bomb test, Castle BRAVO (15 Megatons), which blasted a crater 1.23 miles wide and 250 feet deep. Per @wellerstein.bsky.social, it was “the greatest single radiological disaster in American history.”