Upshot-Knothole Series Test Grable
Operation UPSHOT-KNOTHOLE, the ninth series of atmospheric nuclear tests, was conducted by the Atomic Energy Commission (AEC) at the Nevada Proving Ground (NPG) from March 17 to June 20, 1953. The series consisted of 11 nuclear tests. One detonation was an atomic artillery projectile fired from a 280mm cannon, three were airdrops, and seven were detonated on towers ranging from 100 to 300 feet in height. The operation involved an estimated 20,100 Department of Defense (DOD) personnel participating in observer programs, tactical maneuvers, scientific studies, and support activities. UPSHOT-KNOTHOLE was intended to test nuclear devices for possible inclusion in the U.S. arsenal; to improve military tactics, equipment, and training; and to study civil defense needs.
A single test shot was fired seven miles at the Nevada Test site at 8:30am, local time, on May 25, 1953. A 15-kiloton test fired from a 280-mm cannon at the Nevada Proving Grounds. Conducted at Frenchman's Flat, Nevada, the Upshot-Knothole Series Test Grable was history's first atomic artillery shell fired from the Army's new 280-mm artillery gun.
The Artillery Test Unit from the Artillery Center, Fort Sill, Oklahoma, fired the cannon. Like Shot ENCORE, Shot GRABLE had extensive test group activities; an estimated 650 DOD personnel participated in the Military Effects Group projects. DOD personnel also assisted in Weapons Development Group and Civil Effects Group projects.
Although the scientific program was extensive, many more DOD personnel were involved in the Desert Rock exercises. More than 2,600 exercise troops and over 700 observers participated in GRABLE. Observers, including members of each of the armed services, witnessed the shot from trenches 4.57 kilometers (2.8 miles) west of ground zero. After the shot, observers were to inspect the equipment display area, but due to a dust storm, they were unable to approach closer than 1.37 kilometers (0.9 miles) to ground zero.
After observing the shot with other Desert Rock participants, the exercise troops were to attack two objectives located 2.4 kilometers (1.5 miles) southeast of ground zero and 2.8 kilometers (1.7 miles) east-southeast of ground zero. High winds and dust forced the troops to turn back about an hour after the attack began, although some troops did approach as close as 700 meters (0.4 miles) to the south of ground zero and were able to view the equipment display up to 450 meters (0.3) from ground zero.
For the damage effects evaluation at GRABLE, the 412th Engineer Construction Battalion excavated trenches, bunkers, and foxholes and constructed sections of bridging in the display area southeast of ground zero. The 3623rd Ordnance Company also placed military equipment in the area. Army personnel placed sheep and dosimetry instruments in these fortifications for use in medical and shielding evaluations. After the shot, engineer, ordnance, chemical, medical, and quartermaster teams evaluated the damage to equipment, animals, and fortifications. A veterinary officer and technician evaluated the effects of the detonation on the sheep, and a chemical team retrieved dosimetry instruments.
An unusual event occurred with this test. About the time (afternoon of 26 May) the debris cloud segment stretched between the 5.6 and 9.2 km trajectories was carrying the higher portion of the radioactive cloud across the east coast (over Maryland), a violent hail storm occurred at Washington, DC. Hailstones collected from this storm were tested by the US Naval Research Laboratory there (Blifford et al. 1953) and were found to contain high concentrations of radioactive fission products, particularly high in their centers. High concentrations of radioactivity were also found in the air near the surface, undoubtedly carried to the ground by strong vertical air currents associated with the thunderstorm.
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