The US Central Intelligence Agency (CIA) has revealed it used pigeons to spy on the Soviet Union during the Cold War.
Declassified details now include notes on the CIA's secret Cold War spy-pigeon missions.
Pigeons, it is revealed, were trained for clandestine operations inside the Soviet Union for Operation Tacana, which took place during the 1970s.
Tacana saw the birds trained to photograph sensitive sites and dolphins were used for underwater missions, according to the newly-released files.
The documents also reportedly reveal that ravens were used to drop bugging devices on window sills.
The operation took advantage of the fact that pigeons have an incredible ability. Regardless of where they are dropped, they can find their way back home even if it is hundreds of miles away.
Because of their unique skill, pigeons were already used for intelligence gathering during the First World War.
During the Second World War, the British intelligence service, known as MI14, is reported to have run a Secret Pigeon Service.
The UK intelligence would parachute containers with the birds over occupied European territories with a questionnaire. Those pigeons that returned carried messages useful to predict and counter-act German missions.
With the advent of the Cold War, the majority of British pigeon operations are believed to have shut down, but not the CIA's.
By 1967, the CIA was spending more than $600,000 (today's rough equivalent of $2.2m) on three programmes which involved dogs and spying operations.