The ship-based soldiers of the Colonial Fleet. The Galactica has about thirty of them left, although there are no snipers among them (Bastille Day). Marines' duty include guarding the CIC and Brig (Mini-Series) and assisting the Master-at-Arms (Litmus). They have several times been used, on Raptors, for spaceborne assaults (Bastille Day, Kobol's Last Gleaming, Part II).
Sergeant Hadrian is a Marine, but no officers (if there were any) appear to be stationed on the Galactica; when they are shown on missions, Fleet officers are commanding them.
Their battle uniforms appear to be based on those of the U.S. Army's Delta Force unit or the counter-revolutionary warfare branch of the British Army's Special Air Service Regiment.