Japan launched thousands of intercontinental balloon bombs at the United States during World War II.
In short: Between 1944 and 1945, the Imperial Japanese Army released roughly 9,300 hydrogen-filled paper balloons across the Pacific. Carried by high-altitude jet streams, these unmanned weapons were designed to ignite massive American forest fires. While the campaign largely failed, it remains the first weapon system to achieve intercontinental range.
The Fu-Go project originated from the Ninth Technical Research Institute, a specialized military laboratory. Following the 1942 Doolittle Raid on Tokyo, Japanese leadership sought a retaliatory method to strike the U.S. mainland. Engineers leveraged high-speed, high-altitude air currents—now known as the jet stream—to transport balloons across the Pacific. These devices utilized a complex ballast system of sandbags and barometers to maintain a steady altitude between 25,000 and 27,000 feet, automatically dropping weight to stay aloft during cold nights.
Constructed from layers of durable paper mulberry fiber glued with potato paste, the balloons were assembled by mobilized teenage students. Despite the scale of the operation, the bombs proved ineffective at starting forest fires because the Pacific Northwest was unusually damp and snow-covered during the winter and spring of 1945. U.S. officials maintained a strict media blackout, which successfully prevented the Japanese military from realizing the campaign’s lack of impact. Consequently, the Japanese Army, lacking evidence of success and facing severe resource shortages, abandoned the program in April 1945.
The only fatalities from enemy action in the contiguous United States during the war occurred on May 5, 1945, when a group of civilians in Oregon discovered a landed balloon that detonated. While the military impact was minimal, one balloon caused a temporary power outage at the Hanford Engineer Works, a facility critical to the Manhattan Project. Today, the Fu-Go campaign is recognized as a precursor to intercontinental ballistic missiles, marking a strange, largely forgotten chapter in the history of long-range warfare.
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- Summary by Intellect · source: Fu-Go balloon bomb
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