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Nuclear Test Film - Operation Upshot-Knothole
61 kt · Mar 17, 1953 · Nevada Test Site · 4 Hiroshimas
Operation Upshot-Knothole (1953, Nevada) ran eleven shots, among them Grable — a 15-kiloton shell fired from the M65 280mm 'Atomic Cannon,' the only nuclear artillery round ever detonated in flight by the U.S. The series paired weapons development with elaborate civil-effects experiments.
Aftermath
The Harry shot of 19 May 1953 — later nicknamed 'Dirty Harry' — blanketed St. George, Utah with fallout so heavy that motorists were stopped and their cars washed down. The downwind cancer toll from this and adjacent shots became one of the central grievances behind the later Radiation Exposure Compensation Act.