The locomotion subsystem was a system in Soong-type androids. There was more then one of these subsystems. These subsystems were one of the main sections of the androids, along with the positronic cortex unit, the spatial orientation servo, the primary system module, and the substrate interface. In 2365, when Commander William T. Riker was reviewing the technical specifications for Lieutenant Commander Data, these subsystems were mentioned in the specs. (TNG: "The Measure Of A Man" )