Ahh, the FUGO fire balloons. Very ingenious, and would have caused a great deal of hassle and manpower drain if they had been launched during summer season, instead of the winter of '44-'45.
Basically, a 30-foot diameter doped paper hydrogen balloon, carrying a metal ring assembly which had ballast bags, a barometric switch (to release ballast if it dropped out of the jet stream during flight), a self-destruct bomb (usually a 15kg antipersonnel bomb), incendiary blocks, and a battery for power.
They launched something like 6000 (although 9000 were built) of these from the home islands, and they generally took 3-5 days to arrive in North America. The majority that have been found fell in Alaska, British Columbia and Washington State, but some also in Yukon, Alberta, Oregon, etc. One even made it to Michigan!
There were 6 people killed (a woman and 5 kids) when they found (and probably touched) a balloon bomb while picnicking on Gearhart Mountain, near Klamath Falls, OR, on May 5, 1945. The sole survivor (who was still parking the car when the explosion happened) was Pastor Archie Mitchell of Bly, OR.
The other damage done by the balloons was to short out the electicity at Hanford Plutonium Plant, by falling across power lines. It took three days for the piles to be brought back to full capacity. So perhaps the FUGO delayed the dropping of the first atom bomb by a few hours!
I have a small piece of one of the paper balloons that landed in Canada. It is an aquamarine colour, and has lot of pulp visible. Looks sort of like the hand-made paper you see in chi-chi card shops these days.