Full title: Operation Acoustic Kitty: The CIA spent about $15 million surgically implanting a microphone in a cat's ear, a transmitter under its skin, and an antenna through its tail to spy on Soviet conversations
As far as I can remember it was the Soviets that tried this, but because they practiced this with their own tanks, in battle they would run to the Soviet tanks instead (and blow up there). But I can't vouch for how true the story is.