Rugby Radio Station was a radio transmission facility at Hillmorton near the town of Rugby, Warwickshire in England, situated just west of the A5 trunk road and in later years junction 18 of the M1 motorway. Its large very low frequency (VLF) transmitter came into service on 1 January 1926 and was originally used to transmit telegraph messages to the Commonwealth as part of the Imperial Wireless Chain. After the 1950s this transmitter, active as callsign GBR on 16.0 kHz, using Morse code and later on 15.975 kHz with frequency-shift keying FSK and minimum-shift keying MSK, was used for transmitting messages to submerged submarines. Criggion radio station acted as a reserve.