The earliest examples of cats being used in warfare dates back to the Ancient Egypt during a war against Persia. The Persians, fully aware of the reverance that Egyptians paid to their felines, rounded up as many cats as they could find and set them loose on the battlefield. When the Egyptians were faced with either harming the cats or surrendering, they chose the latter.
During World War I, cats were used in the trenches as an attempt to keep the rat population down and some cats were used as poison gas “detectors”.
The most creative way to use a cat as a weapon happened in World War II. The United States’ OSS (Office of Strategic Services, the precursor of the CIA) needed a way to guide bombs to sink German ships. Somebody hit upon the inspiration that since cats have such a strong disdain of getting wet and always land on their feet that if you attached a cat to a bomb and drop it in the vicinity of a ship, the cat’s instinct to avoid the water would force it to guide the bomb to the enemy’s deck. It is unclear how the cat was supposed to actually guide a bomb attached to it as it fell from the sky but the plan never got past the testing stages since the cats had a bad habit of becoming unconscious mid-drop.
Not to be outdone by its predecessor, the CIA also attempted to use cats but this time as a bugging device during the Cold War. Although a disaster as a guided bomb, the CIA thought that a cat would make the perfect covert listening device in a project known as Operation Acoustic Kitty. They attempted to surgically alter the cat by placing a bugging device inside him and running an antenna through its tail. The project took five years and $15 million dollars before the first field test hit a slight snag when the bugged kitty was released near a Russian compound in Washington and was immediately hit by a car while crossing the street. The project was ended soon after.