When the
atom bomb was developed and the information obtained used to build
Fat Man and
Little Boy (the two atomic bombs dropped on
Hiroshima and
Nagasaki, respectively), the
scientists realized that there was a theoretical terminal limit to the
destructive force an atom bomb could create, regardless of
size.
After World War Two, said scientists turned their research to another type of atomic weapon: the hydrogen bomb. While before there was a restriction due to the laws of physics as to how powerful an atomic bomb could be, an H-bomb can be made as large and powerful as you want it. There was now no limit to the destructive force of an atomic blast, save for size of the bomb and materials used.
For grins and chuckles, the team developing and eventually testing the H-bomb made a big chart listing bomb size and destructive capacity. The list started with your average, run-of-the-mill nuke and gradually went up in size and theoretical devastation as the numbers rose. The last bomb on the list had no projected destructive amount by its size; the scientists had simply wrote "Backyard Bomb" in its space. This Backyard Bomb was named such because it didn't really matter where the bomb was when it went off, it would still mean the termination of every living thing on Earth.
Kinda sobering...
I recalled this from memory. If I got anything wrong please /msg me with the info and I'll change it.