Marine radio may conveniently be treated as a special branch of radio engineering, with its own particular problems and its own technique. No general survey of the field having been published for some time past, this paper has been prepared with a view to placing on record the state of the art obtaining in 1936.The paper has been divided into four main Sections. In the first of these is given a short summary of progress during the last 5 years, with particular reference to the nature and volume of traffic, the types of communication involved, and the growing use of direction-finding equipment by navigators.The second Section deals briefly with the types of radio equipment now customarily fitted in cargo vessels and in passenger vessels other than those which come within the “express steamer” class.In the third Section some account is given of the radio problems encountered in the “express steamer” class of vessel, and of the main equipment items selected to meet the conditions anticipated in the particular case of R.M.S. “Queen Mary.”The last Section deals with the actual radio station of R.M.S. “Queen Mary, ” as built up from the main equipment items described in the third Section, and their associated power supply and aerial systems, etc. The control-room arrangements, which handle four independent duplex circuits, are given in some detail, together with an account of the special precautions adopted to insure efficient multiplex working, quick change of wavelength, high-speed transmission and reception, and simultaneous communication on both telegraphy and telephony with both sides of the Atlantic.