A printed Blue Ensign defaced with the badge of the Royal Naval Minewatching Service on a royal blue field, issuing from wavelets, water bursting up in an explosion, all within a yellow ropework border with a naval crown at the top. The badge is inscribed 'RNMWS'. The design is entirely printed and the flag machine sewn at the ends. 'London 1954' the broad arrow and foul anchor badge, also '3 BREADTHS MINEWATCHING' are printed on the hoist. A rope and two Inglefield clips are attached.

This design was in use from 1952 to 1963 when the name was changed to the Royal Naval Auxiliary Service and the initials to RNXS.

The Royal Naval Minewatching Service was manned by civilians and administered by the Admiralty. It was responsible in wartime for spotting mines dropped by enemy aircraft on major waterways.