Communication Moon Relay

The Communication Moon Relay project (also known as simply Moon Relay, or, alternatively, Operation Moon Bounce) was a telecommunication project carried out by the United States Navy. Its objective was to develop a secure and reliable method of wireless communication by using the Moon as a natural communications satellite - a technique known as EME (Earth-Moon-Earth) communications. Most of the project's work took place during the 1950s at the United States Naval Research Laboratory. Operation Moon Relay was spun off from a classified military espionage program known as Passive Moon Relay (PAMOR) which sought to eavesdrop on Soviet military radar signals reflected from the Moon.

Communication Moon Relay grew out of many ideas and concepts in radio espionage. Some impetus for the project was provided by post-World War II efforts to develop methods of tracking radio signals, particularly those originating in Eastern Europe and the Soviet Union. Other sources included earlier proposals to use the Moon as a radio wave reflector, which date back to 1928. The first proof of this concept was the Project Diana program of the U.S. Army Signal Corps in 1946, which detected radar waves bounced off the Moon. This attracted the attention of Donald Menzel. Menzell was a staff member of the Harvard College Observatory and a former United States Navy Reserve commander, who proposed that the Navy undertake a program to use the Moon as a secure communications satellite.

...
Wikipedia