Quiet and compact oxygen generators may be useful for Navy SEAL missions. Such electrolyzers as closed-loop regenerative fuel cells are potential battery substitutes for applications that require high energy density. Several agencies of the U.S. Government and several private businesses are engaged in development of long-endurance aircraft and airships. The high-pressure electrolyzer developed under this proposed program may be applicable to these vehicles. Large-scale power storage via regenerative fuel cells may have terrestrial applications in telecommunications and other industries that require uninterruptible power supplies. NASA is charged with returning humans to the moon in a permanently occupied lunar station. This mission will require astronauts to conduct extravehicular activities while en route to the moon, and while on the lunar surface. To operate in these environments, the astronauts need an on-site source of pressurized oxygen to refill empty tanks. A very-high-pressure PEM water electrolyzer is proposed that can produce a minimum of 3,600 psi oxygen and hydrogen without the need for high-pressure pumps and/or compressors. A very-high-pressure water electrolyzer will permit smaller launch volumes, saving space aboard the Orion crew exploration vehicle. The electrolyzer might also be useful for the production of hydrogen and oxygen for space vehicle propulsion, enabling missions to Mars. Other electrolyzers of similar designs may be used to produce oxygen and hydrogen for energy storage purposes in regenerative fuel cells on the lunar and Martian surfaces. Other electrolyzers may be used for generation of oxygen on the lunar surface without a net consumption of water through in situ resource utilization (ISRU). By making all of these electrolyzers compatible with one another, if not identical, it may be possible for NASA to save significant development resources while improving astronaut life support safety margins by increasing redundancy.