25 May 1953 – The first atomic cannon was fired at Frenchman Flat, Nevada. Fired as part of Operation Upshot-Knothole and codenamed Shot GRABLE, a 280 mm shell with a gun-type fission warhead was fired 6.2 miles and detonated 525 ft above the ground with an estimated yield of 15 kilotons. This was the only nuclear artillery shell ever actually fired in the U.S. nuclear weapons test program.
The shell was 4.5 ft long and weighed 805 lb. It was fired from a special, very large artillery piece, nicknamed “Atomic Annie”, built by the Artillery Test Unit of Fort Sill, Oklahoma. About 3,200 soldiers and civilians were present. The warhead was designated the W9 nuclear warhead and 80 were produced in 1952 to 1953 for the T-124 shell. Twent were built at the cost of $800K each, and all were retired in 1957.