Operations Grapple, X, Y + Z, were the names of British nuclear tests of the hydrogen bomb held 1956—1958 at Malden and Christmas Islands in the central Pacific Ocean.
Nine nuclear detonations took place during the trials, resulting in Britain becoming a thermonuclear power.
All of the bombs were exploded in the air, rather than on the surface, to reduce the effects of fallout.
From those super-bomb blasts half-a-century ago, sadly the dust has yet to settle