Atomic Annie

The M65 atomic cannon's debut with a test round during Operation Upshot-Knothole at the Nevada Test Site, May 25, 1953. National Archives and Records Administration

I remember hearing about the atomic cannon when I was a kid, but I never saw any evidence of it actually being able to deliver an atomic bomb, so when I came across this on Quora, I just had to steal it. Given the size of the first atomic bombs (big and fat), I wondered how big the bore was. Turns out it was only 280mm, which is only about 11 inches, which is considerable less than the bombs dropped on Japan. Shoot, it's not even as big as the 16 inch guns on some of our battleships, like the Iowa.