Bat bombs were bomb-shaped casings with numerous compartments, each containing a Mexican Free-tailed Bat with a small timed incendiary bomb attached. Dropped from a bomber at dawn, the casings would deploy a parachute in mid-flight and open to release the bats which would then roost in eaves and attics. The incendiaries would start fires in inaccessible places in the largely wood and paper construction of the Japanese cities that were the weapon’s intended target.
The plan was to release bat bombs over Japanese cities having widely-dispersed industrial targets. The bats would spread far from the point of release due to the relatively high altitude of their release, then at dawn they would hide in buildings across the city. Shortly thereafter built-in timers would ignite the bombs, causing widespread fires and chaos.