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 19 seconds after its deployment at 8:30am PDT (1530 UTC) on May 25, 1953, in Area 5 of the Nevada Test Site. As a shell, or artillery-fired atomic projectile (AFAP), the device was the first of its kind. The test remains the only nuclear artillery shell ever actually fired in the U.S. nuclear weapons test program. The detonation of Grable occurred 19 seconds after its firing. It detonated over 11,000 yards (over 10 km, 6.25 mi) away from the gun it was fired from, over a part of the Nevada Test Site known as Frenchman Flat. Public Domain Footage from the US Army. Full HD.