As you can infer from my page on the Fugo or Japanese Balloon Bomb, I think that some of the UFOs seen in the late 40s were Fugos. Below are a few pictures of Fugos and UFOs, see if you can pick which is which....
1
2
3
4
Which is which?
1 is a Fugo.
2 is a UFO
3 is a Fugo
4 is a UFO