As the embers of World War II still smoldered, the world looked to the future with trepidation as the two superpowers emerging from the global conflict—the U.S. and the Soviet Union—began drawing new battle lines. The front lines of the two world wars were gone. Instead, the new boundary lines were drawn with conferences, doctrines, and covert intelligence. By 1947, the Cold War was well underway, and the U.S.’s covert surveillance of its geopolitical adversary began in earnest.

One of those early top-secret initiatives was known as Project Mogul, a sophisticated system of aerial microphones designed to travel into the ionosphere to monitor sound waves emanating from the Soviet Union. After the nuclear bombing of Hiroshima and Nagasaki only two years earlier, the U.S. feared the Soviet Union would soon develop fission weapons of its own (a fear that was eventually realized 1949).