The first truly intercontinental weapon system, Japan's “Fu-Go” balloons were designed to cause widespread forest fires and damage to North American cities, civilians, and croplands during World War II. The hydrogen-filled balloons measured 30 feet in diameter. Each carried a payload of 32 paper sandbags, two incendiary devices, one small bomb, and an altitude regulation mechanism.
Launched from Japan, the balloons would rise to roughly 30,000 feet, where they would hitch a ride on the jet stream and travel at speeds of up to 120 miles per hour eastward. As hydrogen leaked out slowly, the balloon descended. At 25,000 feet, the altitude regulation system would drop one of the sand bags, causing the balloon to rise back to 35,000 feet. This continued until just the incendiary devices and bomb remained; then they too were dropped on the last dips to 25,000 feet. The Japanese launched up to 9,300 of these balloons, but only 300 actually reached North America. They caused six deaths: a woman and five students who happened upon one of the unexploded bombs during a church picnic in Oregon.