The Turret

Space Battleship Yamato with lots of turrets firing in all directions  The Turret 

Definition:  A weapon or weapons mounted on or in an articulation that provides extreme ranges of traverse and elevation, as well as commonly housing the firing/loading mechanism and gun crew.

The turret is one of the most common styles of weapon mounting in SF, and for good reason. Nearly all wet navy guns are mounted in turrets, as are point defence weapons, and the main gun of tanks. It was the invention and adoption of turreted main guns, along with the invention of the steam engine, that changed the face of ocean warfare forever. A spacecraft armed with turrets can bring more of its weapons to bare on any enemy craft, and can do so regardless of its heading. This is obviously important in a battle involving many spacecraft in close proximity, especially those capable of fairly pronounced manoeuvres and high acceleration. Point defence weapons are far far more effective will a turret mount than without, allowing them to track incoming.

There are two common mistakes with the representation of turrets in SF. The first is the idea of a turret as a bolt on unit. While this may be the case for smaller point defence units, it is almost never true of larger weapons. Even the small gun turrets wet navy ships still use extend below the deck level, and old battleship turrets had more concealed than exposed. The second issue is when turrets are placed in a position where the firing arc is limited by other turrets or by the hull of the spacecraft. While the latter is to an extent unavoidable the former defeats the purpose of having a turret to begin with. Yes, I'm looking at you Star Wars.

Disadvantages of the turret are simple. For any given weapon a turret to carry it will add complexity, mass, and power requirements to the design of the combat spacecraft, reducing the overall number that can be carried and increasing the cost. Reduced accuracy can also be a problem due to vibration from the traverse motors, increased vibration in the flexible bearings, and flex in a unsupported barrel. There amy also be a limit to the ammo that can fit in the turret, decreasing the overall firing rate. Unique to spacecraft is the problem that recoil forces imparted on the spacecraft are not going to be constant, and will thus be harder to account for as they impact the trajectory of the whole craft.

Fundamentally turrets have a single advantage; they can be aimed independently of the spacecraft's orientation. All the other advantages - reduction in number of guns needed to provide coverage in terms of point defence, ability to engage multiple targets in different directions etc are all derived from the former. The advantage is most pronounced with point defence weapons, as they will face threats from many angles, and need to be able to track fast and close targets.

Kinetic weapons are ideal for turrets given that unguided kinetics have short ranges, and it is in this envelope that turrets offer the biggest advantage. Lasers also have a lot going for them. Since the laser itself is likely to be in the main hull rather than the turret itself, with the beam reflected through a series of mirrors, there can actually be more turrets than the spacecraft can generate laser light for. Whichever turrets are needed have laser directed into them, and the loss of a few to enemy fire is not such a disadvantage since the total energy output does not decrease. Particle beams benefit the least. This is both due tho their long skinny shape in most designs, and to the fact that bending a particle beam at any kind of angle will produce synchrotron radiation. Tis could of course be overcome by having truely massive turrets or miniaturised particle beams. In terms of point defence lasers are likely to be dominant given their accuracy at range, and the fact that a missile probably won't be too well armoured compared to a spacecraft. Adaptive optics can also give point defence turrets quicker focusing and greater accuracy. Kinetic point defence will be regulated to slower firing 'flak guns' that throw up a wall of shrapnel rather than targeting individual threats.

Unlike broadside and spinal mounts turrets have the best chance of dominance in a softer SF 'Verse. This is because they are best suited to short ranged, high relative speed combat where aim will have to be shifted quickly, and the spacecraft will be changing direction often. They are also suited to battles where enemy spacecraft can emerge unexpectedly from hyperspace in any direction, and in which the spacecraft of both sides end up occupying the same volume of space. Obviously force fields or shields help in this regard as they encourage ships to close to kinetic range where they can output more damage. In a hard science 'Verse close quarters battles are unlikely as everyone will be seen long before they get into range, and with the ranges that are more realistic decrease the disadvantage of fixed weapons and emphasise range and accuracy. Turrets will always be used as point defence installations however, so they will never be absent. A lot of works also feature turret mounted kinetic guns as secondary weapons, like the Sulaco from Aliens; this is quite likly considering the relatively small size that kinetic weapons can have while remaining potent enough to be included.