Just off the top of my head this looks like one of the Operation Crossroads nuclear weapons test carried out at Bikini Atoll in 1946. I believe this was the second of three (planned) tests known as Baker and was carried out on the 25th July 1946. From the shape and size of the explosion and resulting cloud I estimate that the bomb was probably around 23 kilotons and detonated at approximately 90 feet below the water surface. At the time the scale of radioactive contamination was not properly understood and a number of warships were contaminated as well as the local area.

In answer to the question those are huts yes however, to prepare the atoll for Crossroads, Bikini's native residents were evicted from their homes and resettled on smaller, uninhabited islands where they were unable to sustain themselves.

Great suggestion Laurie. Sounds like you know your stuff! :)