Operation Upshot-Knothole Grable

Upshot-Knothole Grable was a nuclear weapons test conducted by the United States as part of Operation Upshot-Knothole. Detonation of the associated nuclear weapon occurred shortly after its deployment at 8:30am PDT (1530 UTC) on May 25, 1953, in Area 5 of the Nevada Test Site. The codename Grable was chosen because the letter Grable is phonetic for, G, stands for "gun", since the warhead was a gun-type fission weapon. It was in the form of a shell, or artillery-fired atomic projectile (AFAP), the first of its kind.

The explosion was an air burst of 160 m (524 ft) above the ground.