Operation Upshot-Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Sit. 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. The codename Grable was chosen because the letter Grable is phonetic for G, as in "gun", since the warhead was a gun-type fission weapon. 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. Operation Upshot-Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site. The test series was notable as containing the first two shots (both fizzles) by University of California Radiation Laboratory-Livermore (now Lawrence Livermore National Laboratory), and for testing out some of the thermonuclear components that would be used for the massive thermonuclear series of Operation Castle. Images of Grable have been misidentified as being Priscilla by the DOE and AEC for many years.