In the 1960s and 1970s, the US Navy researched whether they could use synthesized whale sounds for submarines to have encoded conversations across long distances underwater. Called Project COMBO, it was a fascinating attempt at biomimicry. The project's culminating experiment even attracted a pod of whales. Alas, Project COMBO ultimately failed, but it makes for a great story. From Cara Giaimo's article in Atlas Obscura:
Positioning themselves off of Catalina Island, 150 feet underwater, they blasted their squeaky, warbly codes through a transmitter. The receiver, placed at varying distances away, plucked the messages out of the noise flawlessly. Another test, in the fall, went deeper down and extended the range. In June of 1974, they sent out a real submarine, the USS Dolphin, which successfully transmitted sounds to a receiving ship—and, in a true vote of confidence, attracted a pod of pilot whales.
After these testing successes, researchers were left with a lot of work to do. Although they had the pilot whale on lock, they wanted to expand their repertoire by inventing "techniques and equipment to synthesize large whale sounds and small whale screams." They still had to create scalable versions of their tools, including the call generator and the spectrograph-recognizer. Looking ahead, more problems loomed: the researchers figured this was a good enough idea that the Soviets would steal it, at which point American submariners would need to add another skill to their arsenal. "Fleet sonarmen must become more familiar with bioacoustic signals," they wrote—inspiring thoughts of submarine soldiers, facing long days underwater, taking up sonic seal- and whale-watching.
On the receiving side, submarines were already equipped with spectrographs, which transform incoming sound waves into visual charts. Since the coded pilot whale sounds were synthesized, and therefore identical, receiving and decoding them was merely a matter of recognizing a particular pattern as it came through the machine. A real whale's call, with its unique combinations of pitch and timbre, would produce a slightly different readout, and could be weeded out as noise with the help of recognition software.
"It was never successful," writes Dr. Christopher Willes Clark, founder of the Cornell Bioacoustics Research Program, in an email. "The process of projecting coded 'whale' sounds out to functional distances is not viable." Despite the promise of those initial tests, the technological barriers proved too large to overcome, and subsequent attempts in future years also failed.
Obligatory reference to Star Trek IV: The Voyage Home: