Japanese school children were key to the effort. They spent thousands of hours gluing together 600 pieces of tissue-thin paper to make the 33-foot diameter balloons. About 9,300 balloons were launched in Japan into the jet stream. Filled with hydrogen, the 70-foot-tall balloons were equipped with a mechanism that released sandbags when the barometric pressure indicated when it was time to lighten the load. It took about six days to drop all the bags. At that time the balloons were supposed to be across the Pacific and over the U.S. where they were to drop bombs randomly on the country. The bomb balloons were launched from late 1944 into early 1945. About 300 of them made it to the U.S.
Some of the bombs exploded and some touched down without going off. The press cooperated with the government, keeping sightings out of the papers to avoid a public panic and keep targeting information from the enemy, until May 5, 1945. On that day, one Fu-Go, or “fire balloon” bumped down near Bly, Oregon, where six picnickers from a local church found it and accidentally set it off. The pastor’s pregnant wife and five children from other families were killed in the blast. Newspapers across the country carried that story, with warnings to stay away from bombs and balloons if they were sighted.
What about that balloon bomb near Rigby? It was one of several found in Idaho. One was found between Hollister and Rogerson, one near Hailey, one near Boise, one near Gilmore, and several in the American Falls area. There were no reports of explosions anywhere in the state.
At least two of the balloon bombs came close to important targets. One landed harmlessly in a duck pond near U.S. war ships at the Mare Island, California navy yard. Another balloon got tangled in power lines outside the secret Hanford, Washington facility where fuel was being refined for the atomic bomb that would later be dropped on Nagasaki.