The practicability of utilizing a hydrogen-oxygen-fueled, internal-combustion engine in conjunction with low-pressure cryogenic tanks was determined through an experimental investigation conducted at the Air Force Aero Propulsion Laboratory. This experimental investigation incorporated subcritical tankage with a low-flow cryogenic pump, an internal-combustion power-generating unit, and associated control instrumentation. The development effort concentrated on the improvement of the endurance capabilities of the carbureted hydrogen-oxygen, internal-combustion engine. Specific performance data on all components tested are presented. One of the principal results of the investigation is the recommended use of subcooled liquid hydrogen in the cryogenic pumping system. However, further development effort on both the pumping system and the power generation are necessary before these components can be integrated successfully. (Author).