An early version of what would become known as a spy ship is the
United States civilian
cargo ship , which made frequent voyages to
Japan,
China and the
Philippines with cargo and passengers during the 1920s and 1930s. Starting in 1933 as a station ship she was assigned to monitor internal Japanese Fleet frequencies and direction finder azimuths. She had three intercept operators and one chief radioman supervised by an officer.
Gold Star and ground stations provided significant intelligence before the Japanese attack on Pearl Harbor on 7 December 1941. Spy ships in the modern sense of being specially built and entirely dedicated to intelligence tasks came into being during the early
Cold War, and they are in use by all major powers. Their uses, in addition to listening in on communications and spy on enemy fleet movements, were to monitor
nuclear tests and
missile launches (especially of potential
ICBMs). One of the most important functions for both Cold War spy ship fleets, especially in the 1960s, was the gathering of
submarine "signatures"the patterns of noise that could often identify the specific type of submarine and were thus valuable in
anti-submarine warfare. During that era, the United States fielded about 80 vessels, usually classified as "environmental research" craft, while the Soviet Union had around 60 ships, often converted trawlers or
hydrographic research ships. In the late 1980s, the Soviet
fisheries fleet was known for having equipped many of their thousands of ships with sophisticated
SIGINT and
ELINT equipment, thus functioning as auxiliary spy ships tracking western naval vessels and electronic communications (though their main function remained commercial fishing). ==Operation==