Bat bomb Bat bombs were an experimental World War II weapon developed by the United States . The bomb consisted of a bomb - shaped casing 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 . Overview . The Bat Bomb was originally conceived by a Pennsylvania dentist named Lytle S . Adams , who happened to be a friend of First Lady Eleanor Roosevelt . Dr . Adams submitted it to the White House in January 1942 , where it was subsequently approved by President Roosevelt on the advice of Donald Griffin . Dr . Adams observed that the infrastructure of Japan was especially susceptible to incendiary devices as many of the buildings were made of paper , bamboo , and other highly flammable material . 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 . The United States decided to develop the Bat Bomb during World War II as four biological factors gave promise to this plan . First , bats occur in large numbers ( four caves in Texas are each occupied by several million bats ) . Second , bats can carry more than their own weight in flight ( females carry their young — sometimes twins ) . Third , bats hibernate , and while dormant they do not require food or maintenance . Fourth , bats fly in darkness , then find secluded places ( often in buildings ) to hide during daylight . Project details . By March 1943 a suitable species had been selected . The project was considered serious enough that Louis Fieser , the inventor of military napalm , designed 0 . 6 ounce ( 17 g ) and one ounce ( 28 g ) incendiary devices to be carried by the bats . A bat carrier similar to a bomb casing was designed that included 26 stacked trays , each containing compartments for 40 bats . The carriers would be dropped from 5 , 000 feet ( 1 , 525 m ) . Then the trays would separate but remain connected to a parachute that would deploy at 1 , 000 feet ( 305 m ) . It was envisioned that ten B - 24 bombers flying from Alaska , each carrying a hundred shells packed with bomb - carrying bats could release 1 , 040 , 000 bat bombs over the target — the industrial cities of Osaka Bay . A series of tests to answer various operational questions were conducted . In one incident the Carlsbad Army Airfield Auxiliary Air Base near Carlsbad , New Mexico , was set on fire on May 15 , 1943 , when armed bats were accidentally released . The bats incinerated the test range and roosted under a fuel tank . Following this setback , the project was relegated to the Navy in August 1943 , who renamed it Project X - Ray , and then passed it to the Marine Corps that December . The Marine Corps moved operations to the Marine Corps Air Station at El Centro , California . After several experiments and operational adjustments , the definitive test was carried out on the " Japanese Village " a mockup of a Japanese city built by the Chemical Warfare Service at their Dugway Proving Grounds test site in Utah . Observers at this test produced optimistic accounts . The chief of incendiary testing at Dugway wrote : “ A reasonable number of destructive fires can be started in spite of the extremely small size of the units . The main advantage of the units would seem to be their placement within the enemy structures without the knowledge of the householder or fire watchers , thus allowing the fire to establish itself before being discovered . ” The National Defense Research Committee ( NDRC ) observer stated : “ It was concluded that X - Ray is an effective weapon . ” The Chief Chemist ’ s report stated that on a weight basis X - Ray was more effective than the standard incendiary bombs in use at the time . “ Expressed in another way , the regular bombs would give probably 167 to 400 fires per bomb load where X - Ray would give 3 , 625 to 4 , 748 fires ” . More tests were scheduled for the summer of 1944 but the program was cancelled by Fleet Admiral Ernest J . King when he heard 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 . It is thought that development of the bat bomb was moving too slowly , and was overtaken in the race for a quick end to the war by the atomic bomb project . Dr . Adams maintained that the bat bombs would have been effective without the devastating effects of the atomic bomb . He is quoted as having said : The infamous " Invasion by Bats " project was afterwards referred to by Dr . Stanley P . Lovell , director of the Office of Strategic Services ( OSS ) as " Die Fledermaus Farce . "