Spaceship turret limiting factors

[Comosicus]

I was re-reading IO's "In Memoria" lately (more specific the BFG scenes) and a question remained stuck in my mind: what is the limiting factor in the number of turrets on a spaceship? I understand that 40K likes the "ship of the line" approach to space battles, but what about the rest of SciFi universes? It seems weird to me, for example, that an ISD has only 8 HTL turrets and even those are placed more like a broadside than true turrets. I remember reading somewhere that ISD captains dip their bow to bring all the heavy guns to bear, but again it seems a weird decision. I also discount barel-less weapons like Trek 360 degrees emitters.

I can think of a couple of factors myself, but I would like some other opinions too.

1. length of barrel: broadside or spine-mounted weapons can have longer barrels than those mounted on turrets
2. complexity of mechanisms: a moving turret is more complex / prone to breaking

[atg]

Not sure what you mean by "true turrets" with regard to the ISD. Are you meaning just because they're not on the centre-line? In which case its not like that hasnt happened IRL navies, see some of the early dreadnaughts of the british or german fleets for instance with wing turrets.

[Comosicus]

Not sure what you mean by "true turrets" with regard to the ISD. Are you meaning just because they're not on the centre-line? In which case its not like that hasnt happened IRL navies, see some of the early dreadnaughts of the british or german fleets for instance with wing turrets.

Wikipedia names those "wing turrets" as opposed to "modern turrets" (http://en.wikipedia.org/wiki/Gun_turret). In my opinion the dagger shape of the ISD allows to bring all the firepower to bear ahead by a clever arrangement of the turrets. You'll get then both broadside ability but also a very powerful punch when charging.

Anyway, my initial question was related to the number of turrets. WHY are there only 4 HTL turrets on the ISD on each side? There is plenty of space for so many more. The ratio of volume or surface to number of turrets is so low compared to wet navy ships. What are the reasons for this situation (preferably "in universe" reasons, not "that's how the designers did it")

[Ted C]

There could be many reasons for such a design decision, many of which we wouldn't know. Eight HTLs might be all that the power plant will support, for example. Or each one might require a significant amount of volume under the hull for related mechanisms -- meaning that the entire HTL assembly is much larger than just the turret -- and there isn't enough space for more HTLs plus all the other equipment the designers wanted to include (like hangars, troop quarters, storage for surface attack vehicles, etc.).

[Torben]

As I recall (and to be fair, I performed none of these calculations), the reason for the low number of heavy turrets is simply power output. The ISD2 are stated to have 4 turrets with 8 barrels each, total of 32 per side. Each barrel has an optimal output of 32 teratons per shot, for a total of 1024 teratons per broadside. That's a heck of a lot of energy to throw around, and that does not even consider the numerous smaller turrets (LTL's, point defense, etc).

The ISD was designed (as I understand it) to go toe to toe with other destroyers of the same weight class (as well as perform as a starfighter carrier and assault vehicle), and so carries a weapon complement that allows them to overcome the shielding and armor of a similarly equipped vessel. To place more HTL on that frame would require more reactor space, which would reduce the complement of starfighters and ground troops. The Empire actually did this with the Tector class, but did not produce as many as the Imperator. The ISD fills a role where one ship can be used to pacify an entire star system via its Stormtrooper legion, starfighter units, and light and heavy weaponry.

It's really all about design, usable volume, and the tradeoffs necessary to make a vessel fit its mission parameters - the ISD only needs 4 HTL to perform its assigned tasks, why put more?

[Borgholio]

A modern battleship turret actually has most of it's mass, weight, and machinery below the desk. You only see the tip of the iceberg, as it were.

[Comosicus]

So practically I can design a ship packed full of high powered turrets and batteries, but I will need to have it automatized to the max, and give up other features (like crew and cargo space, hangars) to make place for all the extra generators. Not to mention a way to leak all the heat. Right?

[Borgholio]

So practically I can design a ship packed full of high powered turrets and batteries, but I will need to have it automatized to the max, and give up other features (like crew and cargo space, hangars) to make place for all the extra generators. Not to mention a way to leak all the heat. Right?

Pretty much. Keep in mind that even in the Trek world with the strip phasers, they need a fair bit of equipment under the hull to route power to the weapons. A heavier weapon like a physical turret will need mechanical elements too. You could make a pure gunboat if you wanted, but it'd be like an old wooden ship 'o the line where the crew slept in the same room as the guns.

[Simon_Jester]

I was re-reading IO's "In Memoria" lately (more specific the BFG scenes) and a question remained stuck in my mind: what is the limiting factor in the number of turrets on a spaceship? I understand that 40K likes the "ship of the line" approach to space battles, but what about the rest of SciFi universes? It seems weird to me, for example, that an ISD has only 8 HTL turrets and even those are placed more like a broadside than true turrets. I remember reading somewhere that ISD captains dip their bow to bring all the heavy guns to bear, but again it seems a weird decision. I also discount barel-less weapons like Trek 360 degrees emitters.

I can think of a couple of factors myself, but I would like some other opinions too.

1. length of barrel: broadside or spine-mounted weapons can have longer barrels than those mounted on turrets
2. complexity of mechanisms: a moving turret is more complex / prone to breaking

There are several reasons to limit turret count.

On ships designed like oceangoing battleships, with the turrets as large masses slung out to the edge of the hull, they affect balance and mobility. For real battleships, the turrets had enough weight that the hull had to be braced to hold them or they'd bend down the keel and warp the whole ship. "Wing turrets" slung out to the sides of the ship (like the pair of turrets on HMS Dreadnought) made this even worse by affecting how the ship rolled side to side under wave action.

In space none of those exact effects matter, but having big massive turrets moves the ship's center of mass. Which affects where the engines have to point and where you put the main structural members.

Another practical reason- if ships are armored in a meaningful sense, each turret represents a hole cut in the armored hull. This was a real life problem for ships like the turret-farm HMS Agincourt, which mounted fourteen heavy guns in seven turrets- they might have done better to use four triples. Light weapons that can be bolted to the hull without compromising protection aren't such a big deal, obviously.

Or as noted, heavy beam weapons may consume power out of proportion to their size- it takes a million tons of ISD to provide adequate power, mobility, and protection to ten thousand tons of gun, which makes placing those guns in a handful of protected, flexible turret mounts worthwhile.

Wikipedia names those "wing turrets" as opposed to "modern turrets" (http://en.wikipedia.org/wiki/Gun_turret). In my opinion the dagger shape of the ISD allows to bring all the firepower to bear ahead by a clever arrangement of the turrets. You'll get then both broadside ability but also a very powerful punch when charging.

Firing all eight turrets broadside is easy. Point your broadside at the enemy, then roll 80-90 degrees about the ship's centerline. All guns now bear on the target, assuming your turret elevation will allow it. I'd have to study the detail design to be sure, and I don't care to.

[jollyreaper]

So much also depends on the fluff of the setting. Will an adequate weapon be small enough to fit in a turret or will it need to be keel-mounted? How good are defendes? Is this hammers and eggshells or pea shooters and armor plate? Active defenses vs passive? How survivable are the ships? Can a bigger hull mount a better weapon?

In the age of sail cannon sizes were standard so more firepower meant more decks which meant a bigger and more expensive ship. Battleships could hit harder with bigger guns and a size race commenced. But torpedoes suddenly meant a small ship could knock out a big ship. Guided missiles continued this trend and the top effective warship size is now called a destroyer but has the political clout of a battleship.

There's also the whole argument about size meaning effectiveness. Some people argue a missile boat armed with asm's equals a destroyer with the same but others will argue that the destroyer can deploy further, longer, have better sensors, counter-measures and be more survivable.

There's also the consideration of how much space you have to cover with your military budget. A top battleship can only be in one place at a time and you might end up buying three cruiser equivalents at the same price to cover your areas of responsibility.

You'll see designs remain pretty static once new tech kinks have been worked out and go into flux when game changer tech is introduced. Google the history of mixed armament battleships vs all big guns, torpedo rams, the logic for and against battle-cruisers, etc. Also arguments about armoring up to take the hit or being fast enough to avoid it. Also cases of weapons that might work for one set of tactics completely failing when employed differently.

It makes for long, long reading.

[Borgholio]

It makes for long, long reading.

Yes but rather interesting. The history of making things blow up is never dull.

[Batman]

Actually, it can be extremely dull. And I'm saying this as someone who's actually interested in such things. It all depends on how that history is presented.
Another aspect to consider is that the only inherent advantage more turrets have is the ability to engage more targets simultaneously. Yes, more turrets of the same firepower means more oomph per broadside, but if that's all you want, bigger turrets do the job just fine (as witnessed in modern-world gun-armed warships before missiles made guns mostly obsolete for naval combat anyway), and while more turrets (depending on arrangement) can also mean a greater field of fire, for a spaceship, that can usually be compensated for by simply reorienting the ship.

[Stark]

Depends on how things scale and where the limits are, which an author can just make up. Making single huge cannons was impossible (or impractical) for most of history, but in the land of Admiral Freelancer's Star Patrol it could well be practical. It's so variable between universes that looking for common elements or limiting it to unimaginative historical parallels is probably useless.

[lPeregrine]

It seems weird to me, for example, that an ISD has only 8 HTL turrets and even those are placed more like a broadside than true turrets.

That's not really true. It only has the eight main turrets, but it also has a lot of smaller secondary and point defense turrets that are invisibly small on screen. So its design does exactly what it's intended to do: the maximum amount of heavy guns that the power output can support, placed in a way that optimizes firepower concentration against a single target, with a wide range of secondary weapons to provide full-sphere coverage against anything less than ISD size.

[the atom]

A thought just occurred to me: If turbolaser firepower in SW is mostly just a function of how much can be channelled through the guns, and an ISD's combat loadout is primarily designed with the intent to destroy warships of similar size, then wouldn't it make more sense to just scrap all the broadside turrets and just mount a single, very large turret somewhere on the center-line?

[Stark]

Since it's weapons can apparently already handle some ridiculous amount of its power plants output, what would that achieve?

[Sea Skimmer]

A thought just occurred to me: If turbolaser firepower in SW is mostly just a function of how much can be channelled through the guns, and an ISD's combat loadout is primarily designed with the intent to destroy warships of similar size, then wouldn't it make more sense to just scrap all the broadside turrets and just mount a single, very large turret somewhere on the center-line?

Not really. You now have a single point of failure, even if the turret mounts multiple guns. That's bad for absorbing damage, and its bad because Star Wars is a universe in which stuff actually breaks and needs maintenance. The enemy meanwhile can appear out of hyperspace from across the galaxy with little or no warning. Multiple mounts means its okay that one or more is broken or down for maintenance in the event of a surprise attack. It also means you can engage more then one target at a time, which can be highly desirable for tactical reasons if you can't destroy the enemy with a single shot.


All warship design is a product of a series of tradeoffs, even for simple single role stuff. How those exactly work out in fiction is up to the author, but considerations for turret armament including volume, very important if you have barbettes under the turrets, recoil absorption structure, power for operation, power or ammo for firing, protection of both the mount and the supporting structure and any required power and ammo feeds (local power is always possible, depending on tech, reactor right under the mount or some such), storage for ammuntion if required, safety of said ammo vs other requirements and spaces (do not stack ammo beside the main reactor ect...) and of course, the overall mass of all this stuff vs desired engine performance and fuel load. Cost meanwhile always hovers in the background as a reason not to just endlessly grow the ship to unlimited scale.

If the weapons produce really serious recoil, this could also become a consideration not just in structural terms, but in the ships ability to hold a course. You have no air or water to resist recoil, its going to want to push the ship, thrust vectoring the main engine may suffice to counteract this, but if you had really silly high recoil weapons, like .1% C railguns, on a ship that only weighs thousands of tons, firing 90 degrees to the beam you might need dedicated thrusters to counterbalance it.

Real heavy gun warships were generally limited by overall mass in terms of main battery armament, but at times ships were constrained by volume inside the hull for magazines, generally because other requirements limited the overall size of the ship. This tended to affect sleek cruisers, and ships with large engines or large numbers of secondary weapons more then it did battleship sorts of vessels. Deck space could also become a problem, that's unlikely on a warship that can mount guns without concern for stability.

Since it's weapons can apparently already handle some ridiculous amount of its power plants output, what would that achieve?

Might be cheaper to build, if all you wanted to do was say, bombard a planet. Just not a good idea for ship to ship actions.

[gigabytelord]

I was also thinking, what about battle damage? If you've only got the one center line weapon, and it gets knocked out then what would you do? It makes more sense, to me anyways, that you'd probably want several heavy turrets to simply ensure survivability.

We know that ISDs are generally used in small numbers for most engagements, and it's primary design propose was system pacification, which means that maximum survivability for each ship is paramount in any combat situation, and the best way to make sure something keeps working for as long as possible is redundancy and serviceability.

I may be wrong, but that seems to be the primary reason for designing, building and arming ISDs the way they are.

Ninja edit: Sea Skimmer you beat me to it

[Simon_Jester]

A thought just occurred to me: If turbolaser firepower in SW is mostly just a function of how much can be channelled through the guns, and an ISD's combat loadout is primarily designed with the intent to destroy warships of similar size, then wouldn't it make more sense to just scrap all the broadside turrets and just mount a single, very large turret somewhere on the center-line?

I've heard this one before. Naval reformer and big-gun fetishist Jackie Fisher, when shown an 18" gun bigger than anything ever put on a battleship before during World War One, immediately thought: "Gee, let's mount two of them on a light battlecruiser!" That got him HMS Furious, which turned out to be so moronic that the only way to get performance out of the hull was to rip off the guns and rebuild it as an aircraft carrier.

The one environment where that could remotely make sense is if you're building your 'star destroyer' or whatever to hunt in packs against much, much bigger opponents. Then you get volume of fire from having like fifty ships, you never need to engage multiple targets because you wouldn't last a minute against two of the giants you're after in any case, and you need as much per-shot firepower as you can. For any other purpose it's dumb.

[note, except what Skimmer said. Ships with single giant cannons make sense for hunting anything that comes in singletons and is very large and tough. Including planets.

If the weapons produce really serious recoil, this could also become a consideration not just in structural terms, but in the ships ability to hold a course. You have no air or water to resist recoil, its going to want to push the ship, thrust vectoring the main engine may suffice to counteract this, but if you had really silly high recoil weapons, like .1% C railguns, on a ship that only weighs thousands of tons, firing 90 degrees to the beam you might need dedicated thrusters to counterbalance it.

The bigger threat, I think, is to the ship's structural strength. You can always correct your course after the battle; firing the main guns will impart predictable momentum. The sudden course change might even be helpful because it means incoming enemy fire is thrown off target.

The real problem is firing the gun without bending the ship to a U shape wrapped around its own cannon mount...

I was also thinking, what about battle damage? If you've only got the one center line weapon, and it gets knocked out then what would you do? It makes more sense, to me anyways, that you'd probably want several heavy turrets to simply ensure survivability.

We know that ISDs are generally used in small numbers for most engagements, and it's primary design propose was system pacification, which means that maximum survivability for each ship is paramount in any combat situation, and the best way to make sure something keeps working for as long as possible is redundancy and serviceability.

Yeah. Your biggest design concerns are:
1) Ship needs to carry enough troops and fighters to secure a landing zone all by itself.
2) Ship needs enough heavy guns to blow through a typical planetary defense force, pirate base, or light theater shield
3) Ship needs to be tough enough that it (almost) cannot lose to a significantly lighter warship of any type. What you're talking about is very important to (3).

Incidentally (1) goes a long way to explaining why the ISD's guns look so small compared to the hull. A lot of the ISD's hull space is stormtrooper barracks and giant garages for AT-ATs.

[Lord Revan]

the SW galactic battlegrounds "aircruisers" (actually flying siege cannons) and the SC battlecruiser's Yamato cannon me think of another problem with mounting a 1 big gun instead of several small ones. While a cannon that can take out an enemy with 1 shot sounds nice, what if you miss? There's limits to RoF due to recoil and other things and if you enemy can fire 10 shots in the time it takes you to fire 1 they got the advantace in such case even if they're not able to take you out with 1 hit.

[Simon_Jester]

There are some tricks you can use. For example, if I were building a Starcraft battlecruiser I'd make the 'hammerhead' shape of the bow pretty much a solid slab of heavy, sloped, layered armor. You know the Yamato gun is going to be pointed at the enemy, so you can confidently assume most enemy fire will be coming from that direction. Layering defenses in that direction does a lot to protect the ship from return fire while you reload.

This sort of thing is why a lot of late 19th century artillery pieces had a 'splinter shield' of plating in front of the gun- to protect the artillery crew if enemies with rifles were shooting at them from in front. Knowing that the most likely direction for a threat to be in was 'whichever way the guns are pointed,' it made sense to put some armor up there.

Although real splinter shields were not very heavy and might not stop a real rifle bullet, come to think of it...

[Batman]

the SW galactic battlegrounds "aircruisers" (actually flying siege cannons) and the SC battlecruiser's Yamato cannon me think of another problem with mounting a 1 big gun instead of several small ones. While a cannon that can take out an enemy with 1 shot sounds nice, what if you miss? There's limits to RoF due to recoil and other things and if you enemy can fire 10 shots in the time it takes you to fire 1 they got the advantage in such case even if they're not able to take you out with 1 hit.

Not necessarily. You're presupposing that those 10 shots won't simply bounce off/be absorbed by their shields. Oops-we missed with our megacannon of doom. Since there's jack all you can do to hurt us, we'll just take our time to make sure we actually hit this time?

[lPeregrine]

A thought just occurred to me: If turbolaser firepower in SW is mostly just a function of how much can be channelled through the guns, and an ISD's combat loadout is primarily designed with the intent to destroy warships of similar size, then wouldn't it make more sense to just scrap all the broadside turrets and just mount a single, very large turret somewhere on the center-line?

In addition to the problems already mentioned, the physical size of the turret is a factor. You still have to find a way to rotate the turret at a decent speed, and a bigger and heavier turret is harder to rotate. So your turret gets more complicated, you need more powerful motors to get it moving at the same radial speed/acceleration as a smaller turret, etc. And what if that larger and more powerful equipment is less precise? Now either your guns get a lot less accurate, or you have to wait longer before shooting for your turret to settle precisely on the required aim.

In fact, if the problems like that get bad enough, you might find that your single turret now occupies more space than the sum of all of the smaller turrets. If total firepower is still the same all you've done is make your ship design significantly worse.

You're presupposing that those 10 shots won't simply bounce off/be absorbed by their shields.

But it's as valid a presupposition as the opposite. It's all imaginary hardware anyway, so it's up to the author whether shields/armor/redundant systems/etc are all-or-nothing and either deflect the shot entirely or do nothing to hinder it, or are more of a "hit point" thing where the sum of smaller hits is roughly equivalent to a single larger hit.

[Sea Skimmer]

Although real splinter shields were not very heavy and might not stop a real rifle bullet, come to think of it...

Most of those shields were supposed to stop fairly low velocity shrapnel balls ejected from shells, but many could stop rifle fire at long range. The shields on certain Maxim guns were more questionable which is why they faded away fast. A better example might be the gun shields on world war one cruiser guns though. Frontal and partial side protection, so your fairly safe over a wide arc , but open at the rear and part of the top. Generally they would stop a 4-5in HE shell but not much more.

Partial protection like this could make sense on a very mass critical ship intended for long range fighting, even with turrets.. After all only the thinnest naval turrets normally had the armor equal on all sides. The problem is how many enemies, how many directions of attack seem likely? Longer the range, fewer the enemies, the more focused protection will work of course.

You'd still enclose the rear in any even, even unarmored mounts are likely to be enclosed and look like turrets, just with something really lightweight like foil or fiberglass to provide some thermal insulation and meteorite protection. If nothing else this would make them much easier to work on while in a spacesuit underway.

[Simon_Jester]

Actual armor against serious weapons is heavy- so you're more likely to see spaceships focus protection and deliberately redesign tactics accordingly, compared to the same outcome on land.

On land we give tanks side armor sufficient to defeat whatever weapons we know WILL be fired at them from the sides, even if it reduces speed a bit, because we know damn well we can't stop RPG-armed men from getting around the flanks of our tanks.

In space the mass penalty for armor that can laugh off a proximity-fuzed nuke is high and the engines are (probably) only so powerful, so focusing armor to keep the crew module behind its blast shadow is more desirable.