Crossroads Baker nuclear explosion of July 25, 1946, test fired at 27m underwater. Photo taken from a tower on Bikini Island, 3.5 mi (5.6 km) away.
This is a picture from the 1946 detonation of a 23 kiloton nuclear bomb (same device design that was used to bomb Nagasaki) during operation Crossroads in Bikini Atoll in the Pacific. This tests was designated Baker denoting that it was the second in the series of 3 planned tests (but only two were carried out. The first being Able). It was the 3rd nuclear test ever conducted, and the 5th nuclear explosion in history.
The bomb was detonated 90 feet underwater amidst a fleet of decommissioned US and seized Japanese vessels. It was meant to simulate and document the effects of nuclear weapons in naval warfare.