Squirrel Ninjas would make a very effective Army of Darkness.

I was surprised to learn that the CIA has had a long though not always fruitful relationship with the animal kingdom. In Spycraft, the authors describe many clever animal-assisted devices, from the dead-rat dead-drop pouch to the "acoustic kitty," a cat with a remote listening system embedded in its body. And what's this about the 1 million bats the CIA's precursor, the OSS, were gonna use to firebomb Tokyo during WWII?

The acoustic kitty was a bionic feline with a 3/4-inch radio transmitter embedded at the base of its skull. The transmitter's antenna was woven in to the cat's fur, while the microphone was placed in the cat's ear canal.

The British secret service actually used mice in a similar fashion, not as live microphones, but as a means to drag wire along the studs inside walls. The CIA trained pigeons to fly to laser dots and drop payloads, generally wireless mics. Obviously dogs too were trained for ops—though the Soviets were up on dog training, too, according to Spycraft co-author Keith Melton: the KGB trained dogs to sniff out the glue used by the CIA in equipment drops.

Dead animals worked as well or better. Deceased rats, which apparently had lived long happy lives and died of natural causes, were hollowed out and used to stash secret information for drops in hostile territory. The reasoning was that people don't go around picking up dead rats to see what's inside. As for animals who might be looking for a tasty snack, the rats were painted with Tabasco sauce, repellent to every critter but humans. Fun fact: The CIA used white rats for this, so that they could dye them to match the indigenous coloration of local rats.

Before the CIA was born, live rats—with wings—were considered for strategic use. Project X-Ray a.k.a. BAT was an OSS plan to release 1 million bats rigged with tiny explosives over Japan towards the end of World War II. Bats from Carlsbad Cavern in New Mexico were brought to a test facility. According to Spycraft, the bats' most successful test run resulted in the fiery destruction of a new hangar. The plan was killed off, it seems, because no one knew how to automate the bat-arming process in a cost-effective manner. Bombs were also attempted with the Norwegian rat and trained domestic cats, who were supposed to swim to a target after being dropped in the ocean.