I'm reading howstuffworks.com and came across this old article. I found it interesting and perhaps something that we should be aware of.
http://slate.msn.com/id/2102499/
The Japanese sent 9,000 paper blimps carrying bombs toward the U.S. in WWII.
Snippet:
The censored story was one of World War II's oddest, and it involved a fleet of handmade balloons sent east by the empire of Japan. Improbable though it may sound, from late 1944 through the spring of 1945, the Japanese launched more than 9,000 balloons from their nation's eastern shores. Filled not with mild-mannered hot air but extremely flammable hydrogen and armed with incendiary and antipersonnel bombs, the balloons rode the jet stream across the Pacific Ocean for several days before landing throughout North America.