SPINAL, BROADSIDE, AND TURRETED WEAPONS


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Wherever nerds Science Fiction fans gather to debate the future of space warfare there are several debates that almost always pop up sooner or later, and which  seldom generate a consensus. One of the most popular is the debate over fixed Vs turreted weapon mounts, with the fixed weapons divided into spinal mounts, and less commonly broadside mounts. Related is the discussion over which of the three main direct fire weapons likely to be used in space combat - Laser, Particle Beam, and Kinetic - are most suited to each of the three mounting options. In this blogpost I'm going to attempt a analysis of the specific strengths and weaknesses of each type of mounting, which weapon fits them best, and the tactical scenarios in which they offer the biggest advantages. I'll also cover the worldbuilding needed to justify each option in your 'Verse.

Space Battleship Yamato with the dreaded spinal-mounted Wave Motion Gun  The Spinal Mount 

Definition: A weapon firing in a fixed forward arc, parallel to the direction of thrust, with limited elevation or traverse, and typically running through a significant portion of the spacecraft's length.

Spinal or Keel mounted weapons are interesting because, unlike turrets or fixed weapons, they have no current real-world counterpart aside from fighter aircraft. The sea going battleships that provide inspiration for many SF works used broadsides during the age of sail, and turrets in the era of Big Gun battleships, but a single forward firing weapon has never been used to my knowledge aside from a few submarines like the Surcouf, and that was neither common nor in line with the spinal mounts of SF. If anything their closest analogy is the main gun of a turretless tank hunter. Even that is a poor comparison given the role stealth plays in tank warfare, and the degree to which it is impossible in space.

The rational behind the Spinal Mount is straightforward and pretty logical; the bigger the gun the better, right? Most 'guns' in SF are in fact accelerators of some kind; railguns, coil-guns or gauss cannon, ram accelerators, and particle beams. What this means is that muzzle velocity scales directly with the length of the weapon, rather than their being a optimum barrel length as there is with conventional firearms. There are engineering limits, or those imposed by material science, but the highest theoretical velocity is as close to the speed of light as you can get. A Spinal mount also translates the power of the weapon to the audience quite easily, especially when coupled with long recharge times and/or cool down. The MAC guns of HALO and the Wave Motion Cannon of Space Battleship Yamato are pretty typical of this trope.

There are a few disadvantages with the spinal mount, most of which revolve around the fact that the spacecraft must manoeuvre to aim the weapon. Even if the finer adjustments are done internally rather than by the spacecraft's alignment it will still limit the speed that the spacecraft can edge widely separated targets. It also means that if a enemy emerged unexpectedly from hyperspace the spinal mount might not have time to be oriented before it is destroyed. Most spacecraft armed in this way are shown with only one main gun, with is a disadvantage if it breaks down or is disabled by enemy fire. The spinal mount might well be a glass cannon, extremely dangerous, but needing other ships to contribute to its defence, especially if under attack by multiple enemy.

While the time needed to aim, and the disadvantage of only being able to engage targets in the same direction at once are inescapable the problem of manoeuvrability may not be an issue. A spacecraft equipped with a powerful gauss cannon, railgun, particle beam, or laser, will have plentiful electric power. This can be used to power multiple thrusters distributed all over the spacecraft, rather than having them clumped together, and allowing acceleration in any direction. With many fictional spacecraft the main drives are to large, expensive, or radioactive to allow this, but for more realistic low accelerations electrothermal or plasma based drives may do fine.

The advantages are many. A spacecraft can fit a larger spinal weapon than it could hope to fit into a turret, something likely to hold true for any size of spacecraft. This is partially due to the fact that a turret has to turn, and so has limits on the mass and size of the weapon, and partially to the fact that recoil forces along the line of thrust can be absorbed by the thrust structure instead of by a complicated system of articulation. This can also make the weapon more accurate as it will not have to cope with the vibration of turret articulation, or the fox in a unsupported barrel. Greater muzzle velocity has the advantage of imparting a longer effective range on particle beam and kinetic weapons, helping to negate their inherent weakness. Even if the energy they output is the same as a physically smaller weapon, the increased range will make them more effective at ranged combat, something there is likely to be a lot of in space. And they do not need the cool down time shown in SF. The most powerful might, but it should not be a surprise to find MAC gun like weapon with rapid fire capabilities.

Kinetic weapons benefit the most from a spinal mount as opposed to a turret or broadside since it helps to overcome their greatest weakness - low velocity. Particle beams may also be common in this role since the long skinny shape of a particle accelerator fits the bill nicely. Lasers on the other hand do not seem to be a good candidate. Lasers do not benefit from having a longer physical shape, it is the diameter of the emitter that counts. While there is an analogue — a spacecraft with a single massive mirror at the front — it has its own advantages and disadvantages, and does not really fit the description of a classic spinal mount. Operationally it would be employed the same however, and have the advantage in rage over smaller turreted counterparts.

It is this range benefit coupled with the low turning rate that define the use of spinal weapons. They are the long ranged artillery of space. If they can maintain range from the enemy the extra range might make them well right invulnerable, while if used in a defensive role that extra reach will fore the enemy to run a gauntlet of fire. A battle between two of these spacecraft would be like a sniper duel — few tactics, with the one with the greatest accuracy coming out on top. They would be at a disadvantage in any battle where there are multiple vectors of attack, or one that starts at close range. In a battlefield dominated by missiles they might not fare to well, but one that focuses on direct fire is likely to see them.

The 'Verse that features spinal weapon can fall anywhere on the spectrum of scientific realism. Given their long range and potential firepower it seems likely that any space force will have some in its ranks, and that they will form an important part of tactical doctrine. One thing to note is that they become less attractive as the number and acceleration of ships increases as this brings out their weakness. A jump drive that allows enemy to 'slip under the guns' as it were will also compromise them. In any battle where missiles are unviable, massive firepower is needed from smaller ships, or the enemy will be engaged at extreme range a spinal mount is justified. Another thing to remember is that a magnetic accelerator could be developed as a civilian cargo launcher on the moon, and repurposed as a weapon during a war, similar to in Heinlein's The Moon is a Harsh Mistress. Even particle beams or lasers that fit the design requirements might be developed as part of beamed power stations.