Balloon Bombs: Japan's Answer to Doolittle One of the best kept secrets of the war involved the Japanese balloon bomb offensive. Prompted by the Doolittle Raid on Tokyo in April 1942, the Japanese developed the balloon bombs as a means of direct reprisal against the U.S. mainland. The balloons, made of paper or rubberized silk, carried anti-personnel and incendiary bombs. The first operational launches took place on Nov. 3, 1944, and two days later a U.S. Navy patrol boat spotted a balloon floating on the water off the coast of California. Japan launched some 9,000 balloons during a five-month period, to be carried by high altitude winds more than 6,000 miles eastward across the Pacific to North America. Perhaps a thousand of these reached this continent, but there were only about 285 reported incidents. Most were reported in the northwest United States, but some balloons traveled as far east as Michigan. As more sightings occurred, the government, with the cooperation of the news media, adopted a policy of silence to reduce the chance of panic among U.S. residents and to deny the Japanese any information on the success of the launches. Discouraged by the apparent failure of their effort, the Japanese halted their balloon attacks in April 1945. On May 5, 1945, six picnickers were killed in Oregon when a balloon bomb they dragged from the woods exploded. The U.S. government quickly publicized the balloon bombs, warning people not to tamper with them. These were the only known fatalities occurring within the United States during World War II as a direct result of enemy action. Actual damage caused by the balloon bombs was minor. However, the incendiaries that these balloons carried did pose a serious threat to the northwestern U.S. forests during dry months. These balloons also offered a vehicle for germ warfare if the Japanese had decided to employ this weapon. The balloon attacks began after air defense facilities in the United States had been deactivated. To counter this threat, U.S. Army Air Forces and Navy fighters flew intercept missions to shoot down balloons when sighted. Army personnel and USAAF aircraft were also stationed at critical points to combat any forest fires that might occur. In addition, supplies of decontamination chemicals and sprays to counter any possible use of germ warfare were quietly distributed in the western United States. Before detailed USAAF defensive plans had been put into effect, the attacks ceased. Click here to return to the World War II Gallery. Find Out More Related Fact Sheets Doolittle Raid Note: The appearance of hyperlinks does not constitute endorsement by the National Museum of the USAF, the U.S. Air Force, or the Department of Defense, of the external website, or the information, products or services contained therein.