|Fig. 1: Upshot-Knothole Annie detonation. (Source: Wikimedia Commons)|
Operation Upshot-Knothole consisted of eleven nuclear test shots over the course of March 17, 1953, to June 4, 1953. The experiments took place at the Nevada Test Site located in southeastern Nye County, Nevada, about 65 miles northwest of Las Vegas. The area covers approximately 1,360 square miles of desert terrain. Approximately 2,000 troops were present at the site throughout testing to perform radiological safety, communications, medical care, transportation, etc. 
By 1953 a pattern of test activity had emerged. Throughout the entire decade of the 1950's, about every year a series of several shots were fired at the Nevada Test Site for a variety of objectives. Efforts to prepare the United State's military for atomic bomb combat continued with proof-tests of a number of new tactical weapons, including the first nuclear artillery shell. Operation Upshot-Knothole specifically tested the radiation implosion systems for the first deployable thermonuclear weapons, a critical component for future nuclear tests.
|Fig. 2: The artillery firing of Upshot-Knothole Grable (Source: Wikimedia Commons)|
The first test on March 17, 1953, came from a 300 foot tower shot with a 16kt yield (see Fig. 1). In an effort to calm public fears about weapons testing, Annie was permitted to be viewed by public reporters approximately 11 kilometers south of the shot-tower.  The effect of the nuclear blast was studied on two wooden frame houses, fifty automobiles, and eight bomb shelters. After, it was deemed "relatively safe" to be ten blocks away from the blast's hypocenter if proper shelter was found before the blast.
The tenth test, taking place May 25, 1953 was a 524 foot airburst with a 15kt yield.  This experimented tested nuclear artillery shells shot as an atomic projectile, as the second of only four gun-type warheads ever detonated. (Little Boy was detonated August 5, 1945.) The projectile was shot 11,000 yards, detonating 19 seconds after its firing, yielding an estimated 15 kilotons, the same as the Little Boy (see Fig. 2). The explosion was an air burst 524 feet above its designated burst altitude. A precursor was formed when the resulting shock wave reflected off the ground and surpassed the incident wave due to a heated ground air layer and such low burst height. Altogether, this led nuclear physicists to reevaluate the importance or low air bursts in future tactical nuclear warfare.
Through all the nuclear tests performed, including the eleven of Operation Upshot-Knothole, there still remains more than 300 megacuries of radioactivity in the local environment.  Further, the concentration of radioactivity in the groundwater reaches millions of picocuries per liter, posing a threat to future residents for tens of thousands of years.
© Conrad Ukropina. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Operation Upshot-Knothole," Defense Threat Reduction Agency, July 2007.
 "United States Nuclear Tests - July 1945 Through September 1992, U.S. Department of Energy, DOE/NV-209-REV 15, December 2000.