Storable powerplants are needed in many applications of submerged ocean systems. On the basis of cost effectiveness alone, it is shown that storable fuel cell powerplants for fixed and slowly moving mobile systems offer significant advantages over a range from 0.005 to 30 kW in the mission energy range from 0.01 to 100 megawatt-hr. Analysis of high pressure gaseous storage (compatible with deep submergence hulls) shows significant fuel storage volume advantages over storage of cryogenic hydrogen and oxygen.A unique hybrid fuel storage system, using LOX and high pressure hydrogen at LOX temperature shows reduced displacement, compared to both gaseous and pure cryogenic systems, for modest endurance periods. Long term storage involves substantial volume penalties for cryogenic reactants. High pressure gas storage may, however, be substantially excelled on a storage volume basis by solid reagents used to produce hydrogen and oxygen for the fuel cell as needed. Solid polymer electrolyte fuel cells have reached a high state of technology at which operating life times in excess of 10,000 hr may be expected with negligible deterioation of the cell performance. These thin membrane cells are direct descendents of the highly successful (although shorter lived) Gemini fuel cell system. The advanced membranes have been proven in 40 days of space flight with a bio-satellite mission and year long continuing testing on an advanced Air Force fuel cell program. The combination of solid reagent fuel storage technology and these highly advanced fuel cell modules makes possible a cost effective, compact, and reliable storable fuel cell powerplant for marine applications.