Developed by the United States during World War II, bat bombs were bomb-shaped casings with numerous compartments, each containing a 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. Despite optimistic test results, the program was canceled when it became apparent that it would likely not be combat ready until mid-1945. By that time it was estimated that $2 million had been spent on the project.