Castle Bravo Nuclear Test, Marshall Islands (1954)

The Castle Bravo nuclear test on March 1, 1954, ranks as the worst radiological disaster from a U.S. test, with a yield of 15 megatons—2.5 times higher than predicted. The explosion generated a fireball over 4.5 miles in diameter and deposited lethal fallout across 7,000 square miles of the Pacific Ocean. The Daigo Fukuryū Maru, a Japanese fishing vessel 90 miles away, suffered acute radiation sickness, with one crew member dying six months later. Contamination exceeded safety limits by over 1,000 times in some areas, causing long-term health and environmental damage that outlasts any other test incident, including the 1952 Chalk River meltdown.