Ku-Go Death Ray
Atomic energy changed the face of civilization, and it’s just a matter of luck that the Allies deployed it first. The Japanese military was working on its own secret weapon of mass destruction based on the ideas of inventor Nikola Tesla. The “Ku-Go” was an enormous magnetron that collected and focused microwaves inside a high-powered vacuum tube and directed them in a beam through the air.
Thankfully, available power sources of the era made this a weapon that didn’t ever live up to its full deadly potential, but the Ku-Go could kill a rabbit at a range of 1000 yards without leaving a mark on its body. Sure, it took five minutes to do it, but at least it worked.