The Naval Troopers of the Imperial Fleet Regiments maintained security aboard ship and repelled boarding actions and pacifying escaped detaine. These troopers backed up stormtroopers and were created to provide the Imperial Navy a corps of troops separate from the Imperial Army and the Stormtrooper Corps for protection of their ships.

Imperial Fleet Regiment

Imperial Navy Trooper Battalion

Imperial Navy Commando

Naval Troopers To protect its vast number of capital ships without relying on the help of the Army, the Navy has created a corps of troopers to act as soldiers. These men, trained in traditional combat skills, also learn skills needed to survive aboard the mighty vessels that patrol the galaxy in the name of the Emperor. These troopers wear the distinctive uniform and helmet once only the province of the Death Star troopers. These soldiers dressed in all black are deadly warriors, but they all serve other functions aboard Imperial ships. They act as security, handle hangar traffic control, monitor sensor arrays, and other duties when their combat skills aren't required.
- WEG40092 - Star Wars D6 - Imperial Sourcebook 2nd Ed

Imperial Navy commandos

Imperial Navy commandos were specially trained elite units in Imperial Fleet Regiments. Squads consisted of five to seven commandos and a sergeant, and sometimes an officer or a medic.