Operation Upshot–Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site. It followed Operation Ivy and preceded Operation Castle.Over 21,000 soldiers took part in the ground exercise Desert Rock V in conjunction with the Grable shot. Grable was a 280mm shell fired from the “Atomic Cannon” and was viewed by a number of high-ranking military officials.The test series was notable as containing the first time an atomic artillery shell was fired (shot Grable), 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.