The US Army fired its atomic cannon for the first and last time 68 years ago. The cannon, initially named "Able Annie," was later renamed "Atomic Annie." During the May 25, 1953 test, the cannon fired a nuclear shell that unleashed a 15-kiloton blast. The US Army successfully test-fired an atomic cannon exactly 68 years ago Tuesday. It was the first and only time the US military ever fired a nuclear weapon from a conventional cannon, according to the Army.