A robotic eel may comprise a plurality of torque reaction engines, an inertial mass, and a fin. Each of the plurality of torque reaction engines oscillates an inertial mass about an axis, producing a torque reaction on and oscillation of an external shaft. Oscillation of the external shaft bends a beam of the robotic eel. Bending the beam of the robotic eel produces at least one of a traveling or a standing wave in the beam. The traveling wave may be communicated to a second torque reaction of the plurality of torque reaction engines and to the fin, producing thrust.