When it comes to weapons, it looks like three main types: beam weapons, kinetic weapons, and missiles. Beam weapons are lasers and particle beams. Kinetic weapons are coilguns, railguns, and shrapnel weapons. Missiles are, well, missiles. Ken Burnside compared it to a policeperson armed with a service revolver, a shotgun, and a police dog. The revolver (beam weapon) cannot be dodged or outrun, but can miss. The shotgun (kinetic weapon) is more likely to hit, but with reduced lethality. The dog (missile) can be dodged or outrun (or shot, that would correspond to point defense), but the blasted thing will chase you, and will always hit unless you actively prevent it.
(Holger Bjerre begs to differ. He points out that kinetic weapons are less likely to hit since it can be dodged, beam weapons lose lethality with range just like shotguns, and kinetic weapons do not lose lethality with range just like revolvers. Well, no analogy is perfect...)
Dave Bryant has his own analysis of spacecraft weaponry here. I'm not sure I agree with all of it, so do your own research.
As a general rule, a space warship is basically a "weapons platform." It is just a way to move some weapons that you control into a strategic position in order to rain death and destruction upon enemy military assets.
Weapons are mounted on what they call "hardpoints", "weapon stations", or "static mounts." These are positions on the spacecraft's hull that are designed to carry the mass of the weapon. Analogy: if you are pounding a nail into the wall in order to hang a heavy picture, you pound it into a wall stud, not just the fragile drywall. For the same reason only mount a heavy turret on a hardpoint embedded in the ship's skeleton, not on a flimsy stretch of hull. Otherwise the hull will tear and the weapon will fall off, some hulls are about as strong as a beer can.
Some weapons cannot be mounted on the hull of the spacecraft, for whatever reason they have to be on a small tower called a Pylon. These are generally only found on aircraft, where mounting a missile or bomb directly on the wings will screw up the aerodynamics. But they may be found on weird spacecraft: such as ships streamlined for the interstellar medium (bussard ramjets) or technobabble faster-than-light starships with technobabble fins or something to create FTL or fin-shapes that generate a force field or have wing-shaped reactionless thrusters or whatever the science fiction author thinks is classy sci-fi baffle-gab.
Racks are simplistic hardpoints for weapons you do not have to aim much, typically expendable weapons. Meaning homing missiles and bombs. Technically racks are fixed mounts. They will need some sort of data channel to the ship, so the crew can control the weapons.
Homing missiles are often mounted in "vertical launch systems" or "missile cells", because they do not have to be aimed. Fire and forget, they'll automatically find the target. The missile will jet up in the air a few meters, rotate until it is aimed at the target, then streak to the target on a plume of fire.
Bombs do not have to be aimed much because typically your target is something huge, e.g., a planet or a city. Except for precision bombing.
In addition to missiles and bombs, you can attach to a rack something called a Gun Pod. This is a self-contained detachable modular pod containing one or more weapons, ammunition, and if necessary, a power source. Everything it needs to spit death at hostile ships. Some pods use power from the spacecraft, these require racks with power connection to the ship.
Gun pods are used when mass is an issue, because if the mission does not require weapons the pod can be omitted to increase the spacecraft's payload allowance. They also increase the armaments without consuming internal volume (though this is more of an issue with aircraft than it is with spacecraft). Different types of gun pods also allow a spacecraft to customize its weapons loadout to match a given mission. Snap off the old pod and snap on a ship-killer pod for a knife-fighting range ship duel. Snap off the old pod and snap on a point-defense pod if the mission involves running the gauntlet of hostile missile-fire.
Obviously since a rack is a fixed mount, the spacecraft will have to aim the gun pod by aiming the entire spacecraft. In the real world, gun pods that fire shells or bullets suffer from reduced accuracy. The recoil from the bullets tends to twist the gun pod away from the centerline, unlike bullets fired from a weapon that is integral to the aircraft's skeleton.
If you combine a gun pod with a missile cell you get a rocket pod.
If the rotating mount is attached to the outside of the ship's armor, it is an Installation.
If the rotating mount penetrates the armor it is called a Barbette.
If the rotating mount penetrates the armor and has protective armor encasing the weapon, it is called a Turret. Historically they were first called "hooded barbettes" but the name never caught on.
Apparently there is no term for a turret where the mount does not penetrate the armor, because that is a stupid thing to do. Offhand I think that would be the equivalent of a gun pod with a rotating mount, which would waste a lot of internal pod space on rotating motors.
Some rotating mounts contain two or more weapons arranged parallel. These are called coaxial mounts (although that is a misnomer, used because "paraxial mount" does not go trippingly off the tongue). Obviously all the weapons in the mount fire in the same direction. In the real world you find this often with armored fighting vehicles, with a machine gun mounted coaxial to the main gun. The gunner aims both with the rotating mount, firing the main gun at hard target and the machine gun at soft target.
Sometimes rotating mounts that may have to fire in the same direction are set at different altitudes from the hull, this is called Superfiring. In the real world this is generally found in battleships.
A small turret mounted on top of a turret is called a cupola. A tiny turret mounted on top of a cupola is called a finial.
Conventional turrets rotate to traverse as all turrents do, but elevate by having the gun protrude through a vertical slot and rotate on the gun's trunnion. The gun elevates and depresses but the turret body does not. Since the gun's barrel only covers part of the turret slot, the rest of the slot is wide open for hostile weapons fire. The slot is protected by a mantlet attached to barrel where the gun emerges from the turret. Otherwise enemy fire could enter the open slot, bounce around inside the turret while killing the crew, and maybe even detonating the shell currently loaded in the main gun.
More advanced turrets are Oscillating turrets where the turret is in two parts. The lower turret part rotates, and the upper turret part (and the gun) elevates and depresses. In this case the trunnion is on the upper turret half, not on the gun. The gun protrudes out a circular hole instead of a vertical slot, since unlike the conventional turret the gun does not move relative to the upper turret body.
The three advantages of oscillating turrets are high gun placement, smaller turret size and simpler fitment of an autoloader. All three advantages are because the gun is fixed inside the turret, instead of rotating on a trunnion. I note a fourth advantage: a mantlet is not required.
Having said that, oscillating turrets have rarely been used in historical main battle tank designs.
Broadside mounts that can traverse but cannot do elevation are called Casemates. It looks like a vertical cylinder with a gun sticking out of the side.
Just to confuse things, in historical armored fighting vehicles a tank with a casemate is more like a spinal mount. In other words it is a tank build around a huge tank-killing main gun that you have to aim by turning the entire blasted tank. I only mention this so you are not confused if you encounter it in your research.
Naturally some people who are into hyper-optimization and minmaxing will quickly switch from mounting weapons on a ship, to building the ship around a weapon. A monstrously huge weapon, with a fixed forward facing. It has little or no traverse and elevation because it is a fixed mount.
Of course you will have to turn the entire freaking spacecraft in order to aim the weapon, but the ship is going to smite the target with the most bang for your warship dollar. The ship will also have a similar outline as the weapon, probably long and skinny. This is a problem since long and skinny ships have a large moment of inertia, meaning it will be slow and difficult to rotate the ship while aiming. William Moran suggests that a spinal mount ship has many of the advantages and disadvantages of long-range artillery: they are slow to move and slow to aim but they can utterly obliterate a target at extreme ranges.
It certainly will be the sort of ship that will blast the snot out of you if you are stupid enough to turn around and try running away. Popular spinal mount weapons are coil guns, rail guns, and particle beam weapons, since those weapons inflict more damage the longer the weapon barrel is.
The weapon can be mounted on the ship's nose, along the ship's side ("dorsally" or "ventrally", but RocketCat will rip your lips off if you use those terms, more acceptable is "keel mount"), or along the ship's spine.
You can also be annoyingly clever and spinal mount a weapon that is also a propulsion system. This means the weapon fires to the rear, to give any hostile behind you a quick dose of the Kzinti Lesson. Mass driver propulsion is a good fit here.
In extreme cases the weapon is the ship's spine, this is what the Traveller RPG calls a "spinal mount". A good example is the "Wave motion gun" that forms the spine of Space Battleship Yamato. In the real world the A-10 Warthog ground-attack aircraft is pretty much built around its 30 mm GAU-8/A Avenger Gatling-type cannon. And Matthew Marden pointed out to me that in 1890 the USS Vesuvius was virtually a spinal mount, with "dynamite guns" fixed in both traverse and elevation.
Just to be clever, the Traveller RPG postulated a "Janus mount." This is two half-length spinal weapons installed in a single spinal tunnel, one facing fore, one to aft. In reality there would be no reason preventing two full-length spinal weapons installed side-by-side in the spinal tunnel.
People who have played Star Trek and Star Wars wargames are familiar with the concept of "firing arcs". There are a limited number of direction a given ship-mounted weapon can aim, if nothing else the ship's hull will block off about half the sky. It is generally considered to be a design flaw if a ship's own weapons accidentally shoot off part of the ship protruding into the firing arc. Shooting yourself in the foot as it were.
Different weapons can have different firing arcs, depending upon where on the ship they are sited.
So a combat warship has to maneuver in such a manner to maximize the number of all your firing arcs the enemy is occupying while simultaneously minimizing the number of enemy firing arcs you are occupying. In wet naval warfare, the classic maneuver is Crossing the T. The skillful task force doing the crossing can fire all the broadsides that face the enemy. The unskillful task force can only return fire with the couple of guns each ship has that can fire forwards.
But the battle starts even earlier, as the warship designers try to site the weapon mounts in the most advantageous locations on the ship blueprints.
Spacedock has an interesting thought on weapon placement. Please note that he is making the assumption that for a given warship there will be a preferred range (PR) to an enemy target, a range where your weapon types and ranges will have an advantage over the enemy (example, a ship designed like an artillery piece. Much longer range than conventional weapons, but sluggishly unmaneuverable if the enemy gets too close). This may or may not be true for all ships, but if so it is desirable for your ship to maneuver to keep the enemy within the desired range. Which has an implication:
So if the enemy is at location X, when you approach you want to brake to a halt such that the enemy is at the preferred range (PR). Since you were traveling to location X in order to blow that dastardly enemy ship to Em-Cee-Squared, your vector is pointed right at them. In order to decelerate you have to flip and burn, rotating the ship so that the exhaust is traveling in the same direction as the vector so that the thrust brakes the vector down to being stationary.
See what this means? You are showing your ship's fat ass to the enemy.
Now, assume that you are quote "stationary" unquote with respect to the enemy. Oh ho! That foul villain is burning their jets to get closer, so as to get you inside their PR. You will have to back away from them to preserve your range advantage while they try to close. This means burning your jets in the same direction they are. Yep, this means once again you are showing your ship's fat ass to the enemy.
Why is this a problem? Well, just look at the weapon arcs of most media sci-fi spacecraft. They mostly have all the weapons on the nose. So both while braking to a stop and backing away your weapons are pointed in the wrong direction. Meanwhile an enemy with nose mounted weapons can fire at you with everything they got, right up your kilt.
So logically most of the weapons should be on the aft end of your ship, nestled among the engines. This was actually used in the Babylon 5 episode Severed Dreams, when an Omega Destroyer was running away from a pursuing ship, said ship found out the hard way the Omega has rear-firing guns.
Now, of course things are not quite that simple.
- The video itself notes that it would make sense to mount weapon turrets on outrigger pylons, so they can fire to the fore and to the aft. This would be a good place to use superfiring.
- The video suggest having additional engines mounted on the fore of the ship, not itty-bitty braking thrusters but ones second only to the engines on the aft. I am personally dubious about this because not only is this wasteful of ship mass (cutting into the allowable weapon mass) but also using these engines will turn the floor into the ceiling. A more extreme example is the Globetrotter concept, which I find difficult to take seriously.
- If the enemy is trying to back away from you, then you want your weapons to be mounted on the nose.
- It is possible to use Cascade Vanes to provide reverse thrust. This would allow your ship to slow down and even start backing up while your nose was aimed at the enemy. Drawbacks are it only provides up to 50% of max thrust, and the exhaust has to be cool enough so it doesn't vaporize the vanes.
- Your ship's propulsion system might be dual-use as a weapon. So you can brake with your engine pointed at the enemy AND give them a quick refresher course on the Kzinti Lesson.
- The situation changes if you and the enemy are in orbit around a planet or moon. Raising and lowering one's orbital radius requires thrusting in retrograde and prograde directions. Which can be nowhere near the direction to the enemy.
A Gun Shield is simply a piece of armor attached towards the muzzle of the weapon. It does not provide much protection from any hostile fire except for return fire from your target.
A Gun Mantlet is like a gun shield attached to the base of the weapon, to protect the vulnerable point where the weapon emerges from the turret. In a real-world armored fighting vehicle, hostile weapons fire at that point could detonate the shell waiting inside the weapon. The resulting explosion, occuring inside the AFV would gut the thing. The mantlet's purpose is to prevent that unhappy chain of events.
This is only needed for conventional turrets where the gun emerges from a slot in the turret. The mantlet protects the open slot, or at least the part of the slot not currently plugged up by the gun. In an oscillating turret there is no slot so no mantlet is needed.
A Sponson is a weapon mount projecting from the "side" of a vehicle. It is a term usually applied to armored fighting vehicles. I am unsure how this differs from a turret. Or how it differs from a casemate. In any event, this maps poorly to a spacecraft which does not have a strong "up" and "down".
A Casemate is a broadside weapon housed in a vertical cylindrical armored shell, with a wide traverse but limited elevation. I'm not sure how this differs from a sponson.
A Turret is a gun covered in an armored structure on a rotating mount that penetrates the armor (i.e., it is not attached to the surface of the armor). It typically has very wide traverse and elevation.
A Cupola is a small turret mounted on top of a Turret. A tiny turret mounted on top of a cupola is called a finial.
These are preliminary classification schemas offered "as-is". Tinker with them to suit your taste.
This scheme was created by Erik Max Francis, and contains some modifications by Isaac Kuo:
This scheme was created by Timothy Miller (Cerebus), and contains some modifications by Erik Max Francis: