The present invention includes an underwater vehicle power unit and method of operating the same comprising: a fuel and waste stack comprising one or more reactant or fuel storage bladders and one or more waste storage bladders that are volumetrically and gravitationally balanced during operation; a fuel reactor that generates hydrogen; a fuel cell capable of generating an electrical current when exposed to hydrogen; and a controller that controls the flow of fuel into the hydrogen generator, the flow of hydrogen into the fuel cell and the flow of waste from the hydrogen generator, and/or the fuel cell into the one or more waste storage bladders.

The present invention includes an underwater vehicle power unit and method of operating the same comprising: a fuel and waste stack comprising one or more reactant or fuel storage bladders and one or more waste storage bladders; a heater; a reactor that generates hydrogen and waste; a hydrogen and waste separator; a back-pressure regulator; a hydrogen and liquid separator; a fuel cell; and a controller that controls the temperature of the heater, the flow of fuel into the reactor, the flow of hydrogen into the fuel cell, the flow of water that dilutes the fuel, the flow of waste from the reactor and/or the fuel cell into the one or more waste storage bladders.

The present invention includes an underwater vehicle power unit and method of operating the same comprising: a fuel and waste stack comprising one or more reactant or fuel storage bladders and one or more waste storage bladders; a heater; a reactor that generates hydrogen and waste; a hydrogen and waste separator; a back-pressure regulator; a hydrogen and liquid separator; a fuel cell; and a controller that controls the temperature of the heater, the flow of fuel into the reactor, the flow of hydrogen into the fuel cell, the flow of water that dilutes the fuel, the flow of waste from the reactor and/or the fuel cell into the one or more waste storage bladders.

The present invention includes an underwater vehicle power unit and method of operating the same comprising: a fuel and waste stack comprising one or more reactant or fuel storage bladders and one or more waste storage bladders that are volumetrically and gravitationally balanced during operation; a fuel reactor that generates hydrogen; a fuel cell capable of generating an electrical current when exposed to hydrogen; and a controller that controls the flow of fuel into the hydrogen generator, the flow of hydrogen into the fuel cell and the flow of waste from the hydrogen generator, and/or the fuel cell into the one or more waste storage bladders.

A method for underwater propulsion including a thermal engine system wherein the thermal engine system produces a propulsion gas, the propulsion gas is introduced into a pressure tuned valve, wherein the pressure tuned valve lies upstream of an eductor and the pressure tuned valve controls release of the gas from the thermal engine system to the eductor; and wherein the release of the propulsion gas to the eductor provides underwater propulsion by ejection of the propulsion gas into surrounding water.