"One of the most unusual military actions of World War II came in the form of Japanese balloon bombs, or “Fugos,” directed at the mainland United States. Starting in 1944, the Japanese military constructed and launched over 9,000 high-altitude balloons, each loaded with nearly 50 pounds of anti-personnel and incendiary explosives. Amazingly, these unmanned balloons originated from over 5,000 miles away in the Japanese home islands. After being launched, the specially designed hydrogen balloons would ascend to an altitude of 30,000 feet and ride the jet stream across the Pacific Ocean to the mainland United States. Their bombs were triggered to drop after the three-day journey was complete—hopefully over a city or wooded region that would catch fire.

Nearly 350 of the bombs actually made it across the Pacific, and several were intercepted or shot down by the U.S. military. From 1944 to 1945, balloon bombs were spotted in more than 15 states—some as far east as Michigan and Iowa. The only fatalities came from a single incident in Oregon, where a pregnant woman and five children were killed in an explosion after coming across one of the downed balloons. Their deaths are considered the only combat casualties to occur on U.S. soil during World War II."

https://www.history.com/news/5-attacks-on-u-s-soil-during-wo...