In the aftermath of the attack on Pearl Harbor, America launched the Doolittle Raids on Tokyo. While the actual bombing raids had little impact Japan, it was considered a significant moral victory as it demonstrated that the U.S. could directly attack Tokyo.
In the years following the Doolittle raids, mysterious balloon bombs began decending across the western U.S., Canada, and Mexico. One such device landed just outside Detroit, and in March 1945, one landed at the Handford site where the Manhatten Project research was ongoing.
While the U.S. government kept tight control of the media, the question remained, "Where were these ballon bombs coming from"? The answer was left to the Military Geology Unit where geologists with a few handfulls of sand ushered in the science of forensic geology and helped to end the balloon bomb threat.
Meanwhile, the U.S. responded with bat bombs ....
http://www.theatlantic.com/technology/archive/2011/04/old-weird-tech-the-bat-bombs-of-world-war-ii/237267/