"Atomic Annie" (real name M65 Atomic Canon) was a piece of artillery manufactured by the U.S. in the early part of the Cold War. It was able to fire a 600 pound nuclear projectile about 20 miles. There were 20 of these cannons made, but none of them were ever fired in anger. In fact, only one atomic projectile was ever fired. That test shot was taken at the the Nevada Test Site on May 25, 1953.
Here is two minutes of footage captured during it’s only test shot: YouTube.