The Royal Naval Minewatching Service (RNMWS) was a civilian organisation formed in 1952 as part of the auxiliary forces of the British Naval Service.
Its intended wartime role was to man observation points overlooking ports and strategic waterways, in order to report mines dropped by aircraft.
In 1962, it was transformed into the Royal Naval Auxiliary Service, intended as a short-notice response force to help disperse shipping in British ports in case of a nuclear strike.
References
Royal Naval Minewatching Service Wikipedia(Text) CC BY-SA