A system includes an unmanned underwater vehicle (UUV), a reaction structure configured to deploy from a body of the UUV, and one or more tendons connecting the reaction structure to the body of the UUV, wherein the reaction structure deploys at a depth below the body of the UUV. The system further includes one or more power take-out (PTO) units coupled to or between the reaction structure and the UUV. The system further includes a control unit coupled to the one or more PTO units to convert energy from waves on a surface of a body of water for use in other systems within the UUV.