Dental surgeon Lytle S. Adams conceived the bat bomb after visiting Carlsbad Caverns and witnessing millions of Mexican free-tailed bats in flight. He wrote to the White House, and remarkably, President Roosevelt approved the project. The plan: attach tiny napalm incendiary devices with timed fuses to hibernating bats, load them into bomb casings, and drop them over Japanese cities at dawn. As the casings opened, the bats would disperse and roost in the eaves and attics of Japan's predominantly wooden buildings.
During testing at a New Mexico airfield, some armed bats escaped and roosted under a fuel tank, setting the base on fire and destroying several buildings and a general's car. The project was transferred to the Navy, who continued development until 1944 when it was cancelled in favor of the Manhattan Project.
Post-war analysis suggested the bat bombs might actually have been more effective than conventional incendiary bombing at starting widespread fires, potentially causing comparable damage with far fewer civilian casualties.