Excerpts from GURPS Traveller: Star Mercs
"When the Marines arrive, the party is over."
It can be taken as a sign that the player characters have messed up big time if they end up facing the Imperial Marines in combat. The Marines are the "Big Stick," the "First Team," the "Pros from Dover," and their primary job is to kill people and blow things up in the name of the Imperium. They are only committed when there is a serious threat to the peace and stability of the Imperium, and they never leave a job half-done.
Because the Imperial Marines are the top of the military food chain, players tend to want to demonstrate their own superiority by engaging and defeating Imperial Marines. Some players will spend a lot of time organizing the "perfect" force and equipping it with "perfect" weapons (of their own design, of course) and they want the additional ego boost that comes from seeing their creations defeat the best of the best. In the short term, this can be satisfying for the players, but ultimately will probably be destructive to the campaign.
The best use of the Imperial Marines in mercenary-oriented campaigns is as the "or else" factor, for use when the PCs' machinations threaten to do something the GM does not want to happen. If you have to use them, don't go with half-measures. Marines come in full throttle, with full naval support, orbital bombardment if needed, lots of advance preparation and in numbers sufficient to handle the situation.
Fighting Imperial Marines should be a sobering experience. If the characters manage to get out alive and reasonably intact, they should count themselves among the happy few.
The battery had moved into position under cover of darkness, just a few miles from the Loyalist positions. Six self-propelled guns in light armored housings, waiting for the request to rain high-explosive death on the opposing ground troops.
In the fire direction APC, Captain Mike Berezhinho sipped at a cup of strong black coffee. Out there, the foot soldiers were moving into position for their assault. Any minute now.
His headset spoke quiet words in his ear, and the captain put down his cup. He pressed a key on the comm unit.
"Razor One. Smoke on following co-ordinates," the captain said softly, and repeated the forward observer's request. Seconds later the gun code-named Razor One slammed a round into the sky. The captain picked up his cup, mentally counting seconds.
"Battery, prepare to move. Alternate Zulu Four," he signaled to the commanders of all six guns, the ammunition carriers, and his own driver. The intelligence report said the Loyalist counterbattery radar was inferior, but there was no point in tempting fate.
The headset spoke again, and so did the captain. "Razor One. Up three hundred."
Again Razor One slammed back on its recoil dampers. Berezhinho waited.
The headset spoke softly, and he smiled.
"Razor One, on target. Battery, link to Razor One," he waited while the central fire control computer adjusted the aim of all six tubes. The ready light came on an instant later.
"Battery: Six rounds Hotel-Echo-Delta-Peter, fire for effect."
A second's delay while six crew chiefs verified the proper rounds were in the tubes, and that the trajectory had been adjusted slightly to allow for the different weight of the HEDP rounds. Then six guns fired as one.
Berezhinho keyed the connection to the FO and spoke softly: "On the way."
Autoloaders whined, the guns fired again. Again. The position lit up with fire and thunder, but it was as nothing to what the Loyalists were getting. Soon the counter-battery fire would be coming, but by then the battery would be long gone. Berezhinho smiled again as the sixth salvo crashed out and the command APC started to move. He'd bet good money the Loyalists were regretting their words now. Fee too high, indeed!
Local industry becomes capable of maintaining grav vehicles at TL8, though locally produced grav equipment is crude and unreliable. Caseless and liquid propellant ammunition (also known as binary propellant) begin to be used in small arms, tank guns and artillery.
The TL8 infantryman is dressed in combat armor that provides some fragmentation protection. Vital areas are covered by a flak jacket (see p. GT117) and a light infantry helmet (see p. GT117) helmet with built-in communicator, and a respirator. Armament is the assault rifle, often with a built-in grenade launcher (e.g., M16 with M203 GL, see p. HT115 and 121 or RAM grenades, see p. GT115).
Early laser carbines are available, but are generally reserved for forward observers and elite troops who use their weapons as laser designators.
Some units are equipped for zero-g combat, where the laser comes into its own. Other weapons in common use include the snub revolver and its autopistol variant. Ablative anti-laser armor and early hardened vacc suits (see p. GT118) are issued on an experimental basis.
The 20mm LAG (Light Assault Gun, see p. GT115) is in use for squad support, as well as the much heavier LSG (Light Support Gun, see p. 63) of the same caliber, for use against light armor and higher-tech troops using battle dress.
Infantry missile launchers are in widespread use at the platoon level, with various battlefield tac missiles available.
Tracklaying tanks have reached full development, mounting 5-6" (120-150mm) hypervelocity smoothbore cannon capable of delivering nuclear rounds or missiles in addition to standard rounds. Composite armor makes tanks difficult to penetrate with infantry antitank weapons. Infantry assault vehicles, armored like an MBT but carrying infantry and support weapons instead of a main gun, are deployed.
Light wheeled APCs and armored cavalry vehicles are also in common use. Hovercraft strike vehicles mounting missile launchers and light autocannon make an appearance on some worlds, attempting to outmaneuver the armored behemoths.
Ortillery (orbital artillery) is available, though the technology is in its infancy. Satellites or spacecraft dispense kinetic-energy rods to home on designated targets.
Tube artillery is largely supplanted by light missile launchers and MLRS systems.
Mass driver guns (electromagnetic accelerators) become more common throughout the period.
The wheeled or tracked APC and rotary-wing transport are still standard means of moving troops in the tactical environment.
The vulnerability of surface vessels to ortillery drives most from the oceans. Those few surface ships remaining are armed with laser or particle accelerator weaponry to defeat incoming missiles and with mass driver guns in addition to their own missile armament. Submersible vessels are common, however, surfacing only when necessary for the mission.
Hypersonic aerospace interceptors capable of reaching low orbit launch missiles at enemy vessels, while orbital stations are used to launch unstreamlined combat spacecraft and missiles for beyond-atmosphere intercepts.
Air-superiority aircraft can mount laser weapons in addition to missiles. Strike aircraft are capable of using a ballistic trajectory to reach distant targets, though this relies on a lack of interception capability.
The helicopter is supplemented by a jet-powered vehicle using rotary wings for takeoff before locking them for rapid flight.
Secure microwave and laser comms go some way to offsetting the advances in electronic warfare being made. However, these depend upon direct-line relays such as satellites, which are vulnerable to attack. Interception of sidelobes from tight-beam communications yields dividends in the signals intelligence field. The portable battlefield computer system makes collation of information automatic, greatly simplifying the command process.
Missiles and Special Weapons
The infantry missile comes with a variety of warheads - anti-bunker, anti-armor, anti-air, antipersonnel, bomblet and so on. Each warhead incorporates appropriate guidance systems to its task, allowing the infantry platoon to counter most threats with one weapon system.
Mode of Combat
Most TL8+ combat falls into one of two categories: either close-quarters fighting in urban or other confined areas or else fluid actions in the open, dominated by aerospace craft and contests for control of the "high ground" - close orbit. Close Orbit and Aerospace Control Command (COACC) replaces the Air Force of many nations.
Aerospace combat dominates the ground and water theaters. Close-orbit craft are used for reconnaissance and bombardment of anything that stands still long enough.
Installations are very well hidden or else have impressive aerospace defenses. Combat is three-dimensional in high-intensity areas.
Against insurgents and in built-up areas (including space vehicles and installations), small units of infantry are still the primary means of taking and controlling ground.