OMG at the bottom of the page is a link to a 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 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). 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."
At one point some bats escaped, roosted under a fuel tank, set fire to the testing facility and burned down a hangar as well as the overseeing General's car.
The bats needed to be put into hibernation to get them into the bombs, but sometimes they weren't awake enough before being dropped, so the bats would plough into the ground still frozen.
The project was cancelled just after the invention of the atom bomb, on the grounds that it might do a bit more damage than a few bats. Dr Adams, the dentist who came up with the bat idea, still thought his was better. Don't disagree.
> At one point some bats escaped, roosted under a fuel tank, set fire to the testing facility and burned down a hangar as well as the overseeing General's car.
I wonder if this was the start of the trope about the experimental subject escaping containment and destroying the secret facility.
"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). 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."
That's ingenious, and even more horrific.