I use GT: Ground Forces as my model for Imperial ground troops. Here are the high points in re: the Marines
- The Marines are the Imperium's surgical strike team. They are the Pros from Mora, Personal Violence made manifest. Marine doctrine stresses aggression over finesse and applies that aggression at the fulcrum of the problem. Marines take very few prisoners because when they're done with what they do, there's very few bad guys left to surrender.
- Marine doctrine is as a striking force for in raids. It is long on teeth and short on tail. It has fewer artillery battalions and MUCH fewer vehicles. Most combat service support personnel [engineers, medical, chaplains, logistics, etc.] are Navy.
- Marines use a three battalion regiment model. Each battalion has 4 companies and a small HQ element. This will occasionally be augmented by a company of grav tanks from a Marine Armored Regiment. In standard rotation, one battalion is ashore providing garrisons, training, on leave, and available for emergency deployment, the second battalion is deployed on capital ships [either en masse aboard the squadron flagship or in companies divided among the ships of the squadron] and the third is broken up as ship's troops detachments on cruisers and the patrol vessels of the Reserve Fleets. These unit assignments change on an annual rotation basis.
- The Marines are equipped with the absolute best equipment that is available. That means TL 13-14 Battle Dress and Plasma Guns for the line Marines supported by several in TL 15 Battle Dress with Fusion Guns as support.
- All Marines are drop- and protected forces trained by definition, however they much prefer to deploy in Astrin GAPCs.
- The Marine Regiment is a combat formation and is designed to be deployed together.
- There are no Marine Divisions. The largest Marine unit deployed is the Marine Brigade, a group of two entire regiments with a battalion from Marine Armored. In a Bad War situation, the Marines are mostly deployed as battalions or regiments.