As part of Operation Castle, the United States detonates detonates the thermonuclear weapon Romeo on the Bikini Atoll in the Pacific Proving Grounds.
Castle Romeo was a follow-up to the previously tested Castle Bravo. Romeo exploded with a force of 11 million tons of TNT, about 7 million tons more than expected. Like Castle Bravo, which was also a good deal larger than expected, Castle Romeo's fuel isotope mixtures were misunderstood and not fully mathematically planned.
Romeo wasn't even conducted on dry land. The Bikini Atoll was so devastated by nuclear testing that Romeo was hauled into Castle Bravo's crater on a barge and detonated over the water.
The image shown here became one of the most famous of all nuclear images. It has been used countless times in magazines, newspapers and other media to represent even small fission weapons, even though Romeo was a massive two-stage thermonuclear explosion.