Acoustic Kitty was a Central Intelligence Agency (CIA) project launched by their Directorate of Science & Technology in the 1960s, which intended to use cats to spy on the Kremlin and Soviet embassies.
[1] In an hour-long procedure, a veterinary surgeon implanted a microphone in the cat's ear canal, a small radio transmitter at the base of its skull, and a thin wire into its fur.
[1] Victor Marchetti, a former CIA officer, said Project Acoustic Kitty cost about $20 million.
[3] The first Acoustic Kitty mission was to eavesdrop on two men in a park outside the Soviet embassy in Washington, D.C.
[1] A closing memorandum said that the CIA researchers believed that they could train cats to move short distances, but that "the environmental and security factors in using this technique in a real foreign situation force us to conclude that for our (intelligence) purposes, it would not be practical.