The Broadside

Definition:  Weapons mounted at right angles to the direction of thrust, usually within the main hull of the spacecraft, and with limited traverse and elevation. 

A fixed broadside battery is one of the most uncommon arrangements to be seen in SF, with turrets being far more common. The only one that I can think of in visual SF is the gun deck aboard the Separatist ship at the beginning of Revenge of the Sith. In written works the Black Fleet Trilogy by Joshua Dalzelle had what sounded like a fixed battery of laser weapons on the ship that acts as the setting for most of the first book, but it was never implicitly stated. In the Honor Harrington books the beam weapons were, by memory, in broadside arrangement; a necessity imposed by the gravity drives used. There are also the quite common examples in visual media where turrets are shown that would be unable to fire in any arc except that of a broadside. Most of the turreted guns seen in the Star Wars movies fall into this category, with the Venator Class being a prime example.

The scarcity of this arrangement is not unexpected. With the prevalence of the 'Space is a Ocean' trope it is to be expected that a design philosophy that long ago gave way to turret armament should find little traction. Where it is found it is most often for the visual effect, or because the work is intentionally trying to mimic the battles of the Napoleonic War transposed into space.

There are not so many advantages to this type of design, and the conditions under which it become practicable are quite specific. The main advantages are those shared by any fixed weapon mount. Each weapon will mass less than an equivalent turret, and be simpler in construction. It may be more accurate since it can be mounts straight to the spacecraft's structure via recoil absorbing mechanisms, reducing vibration. Ease of access would also be a big factor, especially with advanced and perhaps temperamental weapons since turrets have never been known as spacious. The weapon itself might also be more massive than a turret could cope with, or have a larger recoil force.

Disadvantages are pretty obvious. Limited traverse and elevation impose a greater need for manoeuvrability on the spacecraft, and run the risk that at close range or high traverse speed a more manoeuvrable target could stay out of the fire arc entirely. This is partially avoided with lasers, since with adaptive optics they can have quite a good arc of fire without the actual emitter being articulated. Since they cannot fire forward the spacecraft is at a disadvantage accelerating toward or away from a target, although this may not be a problem depending on the technology level of the 'Verse. The broadside, and all fixed weapons, are at a disadvantage in a 'Verse where FTL can allow a enemy spacecraft to appear unexpectedly in any direction. The need to rotate the entire spacecraft is going to slow down response times significantly compared to a turreted vessel. Conversely the broadside is more attractive in a hard science 'Verse where you will always see the enemy coming.

A broadside thus falls best into a 'Verse with fairly low accelerations and long engagement ranges. It also becomes a lot more practical if the main offensive weapon is a missile attack from standoff range, especially if it is one involving tens or hundreds of missiles, and possible submunitions. The ability to carry more weapons for the same mass than in turrets, coupled with the greater accuracy and potentially greater effective range would give the broadside ship a very good defence against missile spam attacks. Against such an attack it is the volume, range, and accuracy of defensive fire that will stop your spacecraft from being ventilated by a hypervelocity penetrator, and in this regard the broadside holds the advantage. Also, the greater the number of weapons, the more incoming can be targeted at once.

Lasers or kinetic weapons would be the most practical. Lasers would benefit from having many emitters, allowing more incoming to be targeted at once, and for kinetics it allows a greater overall rate of fire, important given their inaccuracy. With kinetics it could also extend their offensive range by filling more space with metal than would be possible with fewer weapons and making it difficult to evade with low thrust levels; range would still be terrible compared to other weapons however. Charged particle beams could interfere with each other, but a neutral beam wouldn't ave that issue. The soft-kill ability of a particle beam might also prove handy against missile attacks; the beams could even be defocused to fill a huge volume of space with relativistic plasma, providing a potent radiation hazard for any incoming missiles. But without exact numbers it seems impossible to give any of the three weapon types a clear advantage for broadside use; it depends doll on the details of the setting.

Some of you might object to the idea that lasers are better with many emitters, and it is a common debate. Do you use one emitter with longer range, or many smaller? My reasoning is that in a 'Verse where missiles are a viable main offensive weapon they will broadly be able to fire enough missiles with enough submunitions that the extra range is not such a great advantage, more so since a accelerating missile at a half a light second or so is going to be phenomenally hard to hit, and could be travelling at a huge speed by that time. In any case, a computer controlled array of smaller emitters can act as a single larger emitter to some extent, in the same way as many modern telescopes use mirrors composed of multiple segments.

Although not strictly a 'broadside' a missile armed spacecraft might have its storage silos arranged in the same configuration to allow more rapid deployment. With warfare based on missile spam the ability to unleash more missiles in less time might be the best chance at victory, and having the equivalent of a current VLS(Vertical Launch System) might be the ideal. This could also look pretty cool visually while maintaining realism, so take notice Hollywood!