the first turbo-transmission from 1932 used a relatively simple design. it consisted of a single torque-converter for the start-up phase and a fluid coupling for the travel phase which were both mounted on a common shaft. a key feature of this turbo-transmission was the filling and emptying of the hydrodynamic circuit, a principle which was first used in föttinger marine transmissions. this offered the advantages of frictionless start-ups, frictionless gear shifting with constant traction, freewheeling through emptying of the hydrodynamic circuit, and more efficient operation of the fluid coupling.