Put Not Your Trust In Bats
Bats have always seemed to me to untrustworthy creatures - shifty looking, French-sounding squeaking, hanging out upside down. DefenseTech confirms my prejudice.
The idea behind World War II's Project X-Ray "was that a bomb-like canister filled with bats would be dropped from high altitude over the target area," says Murdoc Online. "The bats would be in a sort of hibernation, but as the bomb fell (slowed by a parachute) they would warm up and awaken."
At the appropriate altitude, the bomb would open and over one thousand bats, each carrying a tiny time-delay napalm incendiary device, would flutter away and roost in various nooks and crannies, many of them in extremely flammable wooden Japanese buildings.
The napalm devices would go off more or less simultaneously, and thousands of little fires would start at the same time. Many of them would grow into large fires, and the ability of the Japanese firefighters to contain them would quickly be overwhelmed...
... one afternoon while demonstrating the napalm devices, several bats woke too early in the lab, flew off, and ended up burning down the brand-new but uninhabited Carlsbad Auxiliary Army Air Base in New Mexico.
I'm guessing that this is why they ended up penning the brutes in the Carlsbad Caverns.