Possible inspiration for the film?

Great Britain detonated 9 hydrogen bombs over islands in the central pacific region between 1956 and 1958 code name: 'Operation Grapple'

However the setup of the test detonation depicted in the film differed greatly from the what actually happened. Operation Grapple was one of the largest military operations since WWII with many hundreds of observers and the chances of any civilians getting into the test area without being spotted would have been remote in the extreme. Also the bombs were exploded in the atmosphere - not a ground level.

I liked the film but it felt a lot shorter than its 90 minute running time and the version I saw was colourised which made it look very strange.