This is probably about the only report that actually admits this happened and everything later became Hush Hush and was not published.
The Japanese built high altitude balloons which they launched from japan and the prevaling winds and rotation of the earth brough them to the US.
Most landed in the pacific northwest region in forests and probably many have never been found. Many probably landed in Canada but I have not heard of this.
They carried explosives as well as disease and chemical filled containers.
Japan had experience in China with Biological warefare and what it could do so drop a little on the US.
To build ballons that could make the trip across the big pacific was no small feat.
Apparently it was decided that people in the US should not be told of this and secrecy then surrounded everything to do with these balloons and apparently still does today.
If the American people had been made aware of this there is no limit of what might have happened with reguards to the Japanese people and Japan. Thats my opinion anyway.
In 1946 when the balloon was found at Roswell in a desolate spot on a ranch the army and air force quickly removed what was found.
Which in my small opinion created one of the biggest hoax that ever happened and has spread world wide.
http://www.eugeneleeslover.com/AMMUNITION/REPORT-FROM-HOME.html
