An Endurance Extension Module (EXM) for powering an Unmanned Underwater Vehicle. The EXM converts wave motion to locomotive thrust, towing the UUV from point to point or keeping it in place against an opposing current. The EXM may also supply the UUV with electricity for driving an electric motor or powering on-board electronics. The EXM can be refracted onto the UUV when not in use to minimize drag, or it can release the UUV as prologue to a subsequent rendezvous. The EXM-UUV combinations of this invention allow extended autonomous missions over wider territory for purposes such as surveying, monitoring conditions, or delivering cargo.