Photograph of the mushroom cloud of water and radioactive material produced by the test detonation of an atomic bomb at Bikini Atoll in the Pacific Marshall Islands, on July 25th, 1946 (codenamed: Baker Day"). The expanding radio- active cloud enveloped all but the outer fringes of the waiting observation fleet a few minutes after detonation. The explosion was part of a series of atom bomb tests code-named "Operation Crossroads". The photograph was taken by an automatic camera situated on an island some miles away from the blast centre."