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 . The incendiaries, which were set on timers, would then ignite and start fires in inaccessible places in the largely wood and paper constructions of the Japanese cities that were the weapon's intended target. The United States Navy took control in August 1943, using the code name ProjectX-Ray.
Conception
The bat bomb was conceived by Lytle S. Adams (1881–1970), a dental surgeon from Irwin, Pennsylvania, who was an acquaintance of First Lady Eleanor Roosevelt. The inspiration for Adams' suggestion was a trip he took to Carlsbad Caverns National Park, which is home to many bats. Adams wrote about his idea of incendiary bats in a letter to the White House in January 1942 – little more than a month after the attack on Pearl Harbor.
In his letter, Adams stated that the bat was the "lowest form of animal life", and that, until now, "reasons for its creation have remained unexplained".
President Roosevelt passed the letter to William J. Donovan, the director of the Office of Strategic Services (OSS), in which he attached a cover letter, which read: "This man is not a nut. It sounds like a perfectly wild idea but is worth your time looking into."
The plan was subsequently approved by President Roosevelt on Griffin's advice.
After government approval
thumb|Tadarida brasiliensis, Mexican free-tailed bat
After Roosevelt gave the project his approval, it was relegated to the authority of the United States Army Air Force. Adams assembled the workers for the project, including the mammalogist Jack von Bloeker, actor Tim Holt, a former gangster, and a former hotel manager, among others. Von Bloeker, his assistant, Jack Couffer, and Ozro Wiswell, a scientist, self-described "bat lovers", They also had to decide what species of bat to use for the bombs. After testing several species, the Mexican free-tailed bat was selected. Adams had to ask for permission from the National Park Service for Griffen to harvest large numbers of Mexican free-tailed bats from caves on government property. While the original plan was to arm the bats with white phosphorus, American chemist Louis Fieser, Griffen's former roommate at Harvard, joined the team and white phosphorus was replaced with his invention, napalm. The bats roosted under a fuel tank and incinerated the test range.
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 Ground test site in Utah.
Observers at this test offered optimistic accounts. The chief of incendiary testing at Dugway wrote: