Abstract: A robotic fish comprises one or more torque reaction engines and a fin, wherein the one or more torque reaction engines cyclically oscillate and is to cause one or more waves to propagate through the fin, wherein the one or more waves accelerating thrust fluid and propel the robotic fish. The robotic fish may have a shape of a flagellum, a fish, a marine mammal, or a disc. The one or more of the one or more torque reaction engines may comprise a drive shaft or may comprise no drive shaft. When the one or more of the one or more torque reaction engines comprises no drive shaft, the one or more of the one or more torque reaction engines may comprise a bearing surface of a closed ball-and-socket joint.