An unmanned underwater vehicle propulsion system includes a turbine engine having a mechanical output, an electrical generator including a mechanical connection to the mechanical output, and an electrical input/output. At least one power bus connects the electrical input/output to one of a motor drive and a motor. A rechargeable energy storage system is connected to the at least one power bus and is configured to provide power to the power bus in at least a first mode and receive power from the power bus in a second mode. A controller is configured to control at least one of the electrical generator, the motor drive, the motor, and the rechargeable energy source.