The Atomic Cannon was a thing during the Cold War
On May 25, 1953, the U.S. military tested a 280 mm atomic artillery shell over Nevada it codenamed Grable. The round was fired from the Atomic Cannon—one of the largest ever produced by the U.S.—to a target seven-miles away.
The U.S. made 20 of these cannons during the Cold War in case it came to blows with the Soviets. The round detonated in the air and completely obliterated the cars, buildings, and bridges below.