A reasonably hard military fire service cap badge to obtain, in force for only 12 years and part of the the Admiralty Constabulary Fire Brigade / Police, a body set up in 1949 from former Naval related firefighting services. In 1956 a review of the provision of fire protection in HM Naval Dockyards, many were reduced or disbanded leaving main firefighting to regional county and county borough fire brigades. However the 4 major dockyards, Portsmouth, Rosythe, Devonport and Chatham remained under the control of the Admiralty Constabulary Fire Brigade and this badge was introduced to distinguish fire brigade personnel from police personnel. It is a Home Office produced fire badge which means Crown Copyright makes reproducing these cap badges a criminal offence ! 
This cap badge, a one piece pressed badge with an enamel red ring centre containing a chrome anchor, standard Royal Naval symbol on all of its badges,  a standard slider cap fitting as a lot of military cap badges are, was probably manufactured by William Dowler Badge Company of Birmingham who supplied the majority of Home Office fire brigade related cap badges. The badge is in good original condition and a not easy badge to obtain.