What is the address HM fleet in foreign waters? The General Post Office; St Martins Le Grand; London; is the address of His Majestys fleet whilst in foreign waters. There are two reasons for this; the main one being that Post Office officials are in possession of a programme of fleet movements; and may plan ahead where correspondence should be directed abroad; to avoid any undue delay. The other reason is that it preserves a certain amount of secrecy as to the location of any vessel; or unit; when it is considered desirable to suppress fleet information. Illustration for one of a set of 50 "Do You Know?" cigarette cards issued by Carreras in 1939.