Operation Crossroads atom bomb test. Mushroom cloud rising from the Baker atomic explosion carried out at Bikini Atoll, in the Pacific, at 21:34 UTC on 24 July 1946 as part of Operation Crossroads. Baker was the first underwater nuclear detonation. The yield was thousands of tons of TNT, with the column of water vapour reaching thousands of metres into the air. The explosion and wave of water overwhelmed and sank unmanned test ships left in the vicinity. These ships are seen across lower centre. Photograph donated by Commander Gerald P. Pulley.