The properties of water as a lubricant are discussed and the problems of practical hydrodynamic lubrication with water are shown to be capable of solution. From this basis, two general marine bearing applications are considered, the first involving large relatively low-speed bearings, and the second smaller high-speed bearings. For bearings in the first category, such as stern-tube and A-bracket bearings, it is common practice to use water as the lubricant, but it is shown how such bearings may be considerably improved in the light of water-lubrication research, and full scale tests culminating in service in a warship are described. For smaller high-speed bearings, in which at present the lubricant is almost universally oil, it is suggested that in many cases considerable advantage would be gained by using water-lubrication. To illustrate the feasibility of this, the development of water-lubricated journal and thrust bearings suitable for a main turbine is described, together with the operation of a turbine with such bearings, and the practical implications of this work are discussed.