That said, the Japanese weren't stupid and they figured out how to use the jet stream to send their balloon bombs across the Pacific.
As a side note, the Japanese were closer in 1945 to producing an atomic bomb than Nazi Germany ever was. This says a lot for Japanese scientific abilities.
Hey, I could use the jet stream to send balloons across the Pacific Ocean, too. What I can't do, however (and I don't understand how anyone in 1945 could have done it), is: 1) ensure that it follows a precise track that takes it directly over the U.S., and 2) runs out of air over the U.S. (as opposed to landing in the Pacific Ocean, the Atlantic Ocean in Europe, or -- heaven forbid -- floats all the way around the world and lands in Japan).