A relay league is a chain of message forwarding stations in a system of optical telegraphs, radio telegraph stations, or riding couriers.
Radio amateur message relay operations were originally conducted in the first two decades of the 20th century using Morse code via spark-gap transmitters.
As vacuum tubes became affordable, operations shifted to more efficient manual telegraphy transmitters, referred to as CW (Continuous wave).
Messages were relayed station-to-station, typically involving four or more re-transmission cycles to cover the continental United States, in an organized system of amateur radio networks.
After World War II, voice and radioteletype implementations of the message relay system were employed.