We watched "History Detectives" on PBS last night. They were investigating Japanese Balloon Bombs used during WW2 to carry explosives and incendiary devices to the western United States. I'd never heard of them before and what I found interesting was the fact that many of the devices were never recovered and could still be laying around somewhere in any of the little explored parts of the western states. Wouldn't that be an interesting find!? (of course, they could still be armed and explosive so it's best not to touch 'em if you do happen to find one.)
Here's a couple of stories I found about them.