Instituted in July 1965 and awarded for 12 years service in the Royal Naval Auxiliary Service (RNXS). The RNXS was formed in 1963 from the Royal Naval Minewatching Service and the Admiralty Ferry Crews Association. It was disbanded in 1994.
Bars were awarded for a further 12 years service. Approximately 1,700 medals were awarded, 131 with one bar and 2 with 2 bars.