In this research and development project the feasibility of a new type of low inertia electrical servo actuator, designated Electromagnetic Harmonic Drive, is demonstrated. Drastic reduction in inertia, compared to conventional electrical devices, provides for increased power rate, power rate to weight, and power rate to electrical loss characteristics, which are shown to best determine the usefulness of an actuator for fast response, light weight, efficient servo systems. A fundamental analysis is made of the requirements for optimizing these parameters. The relative feasibilities of various electromagnetic configurations for meeting these requirements are discussed in depth. It is shown that two forms of the electromagnetic Harmonic Drive concept offer the most promise. The first is a stepping device which offers all the advantages of digital control systems. It has the higher response capability and is therefore the primary type. The second form is a synchronous device with constant torque output but a somewhat lower response capability. Implications upon electrical control systems, resulting from the advance in performance provided by the new device, are discussed.