 References are frequently made to Starfleet "ground troops," and  some Starfleet characters have different uniforms (a black uniform  with a small colored stripe across the middle). Fans generally  accept that these characters are part of a Starfleet Marine Corps,  although this has never been explicitly stated onscreen. There was a  Starfleet Colonel West in  _Star Trek VI: The Undiscovered Country (1991)_ (qv); West was most  likely a Starfleet Marine, since navies do not have the rank of  colonel.