The purpose of this Hydrospace Information Report (HIR) is to define materials for use in fluid systems of marine vehicles, including submersibles and advanced surface craft. This report is more particularly directed to the designer of fluid power and piping systems on board marine vehicles. The scope of this HIR is to delineate groups of materials for which there is considerable fabrication and operating experience in the sea water environment. In addition, some of the more promising materials for possible future applications are covered