Originally, engine control systems consisted of simple mechanical linkages connected physically to the engine. By moving these levers the pilot or the flight engineer could control fuel flow, power output, and many other engine parameters. The Kommandogerät mechanical/hydraulic engine control unit for Germany's BMW 801 piston aviation radial engine of World War II was just one notable example of this in its later stages of development.[2] This mechanical engine control was progressively replaced first by analog electronic engine control and, later, digital engine control.