The date was 25 July 1946. The location - Bikini Atoll. The event - only the fifth A-bomb explosion and the first-ever detonation under water.
The pictures we've all seen: A giant mushroom cloud climbing out of the Pacific, sweeping up ships that had been deliberately left in harm's way to see what nuclear war was capable of.
Now, 73 years later, scientists have been back to map the seafloor.