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. This incident outperforms #10 Chalk River in immediate human casualties and global fallout, forcing the evacuation of Rongelap Atoll and sparking an international movement for a test ban. 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.