Innovative technology was commonly used for military purposes in World War II, most spectacularly when Germany launched the high-tech V-2 rocket against England. Japan used a low-tech, but no less dangerous, weapon against the United States. Taking advantage of prevailing westerly wind currents across the Pacific, Japan launched thousands of high-altitude balloons armed with bombs to float across the ocean and explode in the United States. Nearly 300 made it to the West Coast, some landing as far east as Iowa and Kansas. Most failed to detonate, but a few did spark wildfires, and six people were killed by a bomb explosion in Oregon. Government authorities kept the balloons a secret because they were afraid the Japanese would be inspired to launch more balloons if they knew some had reached their target.. The secrecy was effective, and the Japanese soon abandoned the project, a decision...