The trouble with spying is that it's a terribly time consuming process relying on electronic surveillance or using people to either break in or secretly pass on confidential information. The CIA realized that both of those approaches were not only fraught with inefficiencies, so why not remove man and machine out of the equation?
In the 1960s, the CIA launched Operation “Acoustic Kitty”, a $20 million ($160 million in 2018 dollars) project with the goal of spying on the Kremlin and Soviet embassies.
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. This would allow the cat to record and transmit sound from its surroundings.
The first Acoustic Kitty mission was to eavesdrop on two men in a park outside the Soviet compound on Wisconsin Avenue in Washington, D.C. The cat was released from the house across the street from the Russian Embassy at 2619 Wisconsin Ave NW, but was hit and allegedly killed by a taxi almost immediately. After the project was cancelled in 1967, 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."
When details about Operation Acoustic Kitty came to light in 2001 when some CIA documents were declassified, a former Director of the CIA's Office of Technical Service disputed some details, saying that the project was abandoned due to the difficulty of training the cat to behave as required, and "the equipment was taken out of the cat; the cat was re-sewn for a second time, and lived a long and happy life afterwards".
Today the house stands in its original condition as one of the greatest spy homes to have ever existed.