52HertzWhale

In the late 1980s, the U.S. Navy was routinely monitoring the Pacific Ocean for something far removed from marine life—enemy submarines. Using the Sound Surveillance System (SOSUS), a vast network of hydrophones originally designed during the Cold War to track Soviet submarines, Navy analysts were accustomed to picking up a variety of underwater noises—the deep calls of migrating whales, the rumble of shifting tectonic plates and the distant echoes of ships cutting through the waves.