The Atomic Cannon
This retired weapon was designed and deployed (but never fired in battle) at the height of the Cold War (1953-1963). The intent of this 280mm cannon was to fire a nuclear shell a tactical distance to benefit the artillery crew so they wouldn't be killed by the blast and radiation as they took cover in trenches during the firing. The Atomic Cannon was test fired in Nevada in 1953. You can see the M65 280mm atomic cannon at Yuma Proving Ground's entrance gate, along with other retired weaponry including rockets, tanks, and a 200mm gun-howitzer.