Bat bombs were an experimental World War II weapon developed by the United States. The bomb consisted of a bomb-shaped casing with over a thousand compartments, each containing a hibernating 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 disperse and roost in eaves and attics in a 20–40-mile radius (32–64 km).