Largest Possible and Feasible Battleship Armaments

[Delta Force]

So, I'm just wondering what the largest possible and feasible battleship armaments would be. Historically the 18 inch was useless because the USN used 16 inch superheavy shells which actually had better performance for a much lighter gun and battleship. So I was wondering, is the 16 inch the largest useful caliber, or is it something smaller or even possibly larger?

[Guinness]

Historically the 18 inch was useless because the USN used 16 inch superheavy shells which actually had better performance for a much lighter gun and battleship.

This is a strong statement, and of a sort often seen on certain message boards where historical and ahistorical ships and armament are discussed, but I for one don't agree.

It may be true that ships armed with the US 16" Mark 6 and Mark 7 guns firing Mark 8 2700lb "super-heavy" projectiles could have defeated ships armed with the Japanese 46cm Type 94 gun firing it's 3219lb round. Or maybe they would not have. Since they never met in battle, we'll never really know for sure.

This brings me to:

So I was wondering, is the 16 inch the largest useful caliber, or is it something smaller or even possibly larger?

The USN did not know that the Yamatos were to be armed with 46cm guns. So the USN persisted with the 16" gun series as the largest caliber permitted by treaty, after they had invoked the escalator clause during the design of the Washington class. Had they known about the true size and armament of Yamato, I believe that a program to develop an 18" gun would have been undertaken with priority. The USN had been in the process of developing the 18" Mark 1 at the time of the signature of the Washington Treaty, so some work had been done, though I expect a late-30's 18" gun would have been of a completely new design.

Now an 18" main armament would have presented some challenges of design. It seems reasonable to expect that 8 18" guns of some new design might weigh about as much or even less than the 12 16" Mark 7's planned for the Montana's, so an "upgunned" Montana might have been the result.

Now, once war breaks out, the parameters of the decision making change. It's possible, had revelation of the Yamato's armament and size come about during the war that the existing Montana design would have been persisted with, so as not to screw up production schedules, etc. by introducing a revised design and a new gun. Certainly the US was not hesitant to persist with less than optimal weapon designs only because they were already in production.

Now to the meat of your question: the parameters of when a ship would be too big to be useful depend on the requirements and limitations of the navy building them. If you'd ask naval engineers in 1910, they'd have said ships bigger than about 30k tons were likely impractical. Ask the same question of their successors, and the number might have been 60k tons. Every navy had limitations of dock sizes, harbor depths, etc. etc. to contend with. Still, given that I believe a Montana with 18" guns was doable, I suspect the maximum useful caliber was probably 18". Even so, by 1940, it's likely only one nation would have been able to afford more than a couple such monsters.

I think it is true that somewhere around 15" or 16" there starts to be an effect of diminishing marginal returns as caliber increases, since ship size increases that much faster.

[Kaiser Kirk]

There is not really a definitive answer. Further, the answer may change with technology.

It's hard to answer "correct".  
Gun design and choice varies with OPFOR and expected combat ranges.  The North Sea has generally short visual ranges, the Pacific longer. If expected combat is at 15,000 yards in the North Sea, then deck penetration is probably not your first concern on what makes the gun "better". Fast, flat arcs and a good ROF become of interest.  

In general, I am given to understand from what others have said the Brits investigated >16" guns- fielded some 18", and decided that the gains really diminished once you pushed past 16-16.5". I can't recall reading it first hand though.
Rate of fire, training rate, rotating weight, blast effects, all offset performance gains.

As for the 18.1" vs 16" thats a dependant on several things.

Even various armor pen formulas disagree a bit on penetration.

Navweaps gives figures for many main battery guns, citing books which apparently based on the USN Empirical Formula for Armor Penetration

Here are some sample figures using that :

18.1"/45 3,218AP   21,872yds  Belt Pen* 19.43"  Deck pen 4.3"
16"/50 2,700AP  20,000yds Belt Pen* 20.04" Deck pen 3.9"
16"/45 2,700AP 20,000yds Belt Pen*17.62"  Deck pen 4.29"
16"/45 2,048AP 20,000yds Belt Pen*12.2"  Deck pen 2.85"
15"/52 1,765AP 19,685yds Belt Pen*16.5"  Deck pen 2.96"
15"/42  1,938AP 20,000yds Belt Pen*11.7"  Deck pen 3.1"
14"/50 1,500AP  20,000yds Belt Pen* 13.75, Deck pen 3.02"
14"/45 1,590AP  20,000yds Belt Pen*11.2"  Deck pen 2.85"
12"/50 1,140AP 20,000yds, Belt Pen*12.73  Deck pen 3.1"
11"/54  727.5AP 20,013yds Belt Pen*11.47"  Deck pen 1.87"

*belt pen would of course vary by aspect, and even ships roll. Deck pen would vary a bit more.

Note that the 16/45 on SoDak is getting better Deck Pen than the 16"/50 on Iowa, and the 18.1" is beating both, while KGV's 14" is equaling Nelson's 16" at that range.  Meanwhile the Alaska's tiny shell is "better" than KGV's, while Scharnhorst's exceeds it in Belt Pen.

MV and shell weight have a great deal to do with shell performance. Shell design matters too- the Brit 15"/42 got "better" late WWI with the new Greenboy shells, while the Japanese 18.1" was hindered by a shell design that optimized diving performance by featuring a fairly flat face- which detracted from it's armor penetration ability.

Then there is technology as well. Earlier efforts at "superheavy" shells by the Brits saw the rear of the projectile fail at oblique angles, rendering the shell useless. Shell design wasn't up providing that. At that point "larger" is needed for the same performance. Further, a "superheavy" 18" would be "better" than a 16" shell with the same technology.  The USN simply came up with really stiff heavy bodied shells- but a 16" super heavy had less explosive filler than some.

Going the other way, really fast light shells are nice against mid-range belts, but tend to suffer dispersion and aren't so hot against decks. There is also probably a scaling effect if the shell is smaller than the plate thickness.

One of the theories floated with the KGV class was that as all battleships were adequately armored for expected combat ranges, so penetration was unlikely, and having a larger quantity of large shells hitting the target would be more important that fewer heavier shells.

[miketr]

I would say that 18" weapons are the upper end of feasible and 16-16.5" will do any job you care to set to it.

Michael

[Logi]

I personally design for 14-15" guns simply because I find it to be a case of diminishing returns. Anything that can withstand 15" shells can probably withstand 16" shells. As such, increasing the caliber and thus the ship size and constraints is not worth it.

So like Kirk noted,

One of the theories floated with the KGV class was that as all battleships were adequately armored for expected combat ranges, so penetration was unlikely, and having a larger quantity of large shells hitting the target would be more important that fewer heavier shells.

There's such an effect going both ways. That's what one of the things I was referring to when I said LOS thickness isn't the best way to calculate whether something will penetration or not.

There is also probably a scaling effect if the shell is smaller than the plate thickness.

[ctwaterman]

Like Guinness and Kaiser Kirk Said....size is dependent upon proposed tactics and arena of combat.

There are rummor has it that beyond a certain size barrel life and wear become serious issues given the metalurgy of the time.  And designing for barrel replacement or relinning after 1 full load out of shells become a concern.

On the other hand there is nothing preventing you from building some of the German H class battle ships weighing in at over 80K tons and armed with 24" guns I believe except the Richmond Treaty/Agreement and well the depth of Norfolk Harbor.

Charles

[Jefgte]

IMO, We must be realist  & limit the size of the max BB to the Liners.
Queen Elisabeth - Queen Mary - Normandie.


Jef

[P3D]

I don't think barrel wear is a limiting factor. If it becomes excessive, some MV could be traded for less barrel wear. Or, load the gun very hot, but make sure that replacing the liners (or the whole gun) could be done fast. The Italians thought it was worth it, and consistently pushed the design to its limit. Their 16" guns would have had some monster performance (assuming they manage to get rid of quality control
issues at propellant manufacturers).

One major issue is how much you rely on the human muscle. The US did it a lot - iirc the Japanese 18" turrets had significantly lower crew requirement, as they moved their shells by machinery to a greater extent.

The main issue rather is that going over 18" one is getting into some serious design constraints. Allowed draught and beam on waterways, drydock sizes, finite budgets. The ship would also need to make a given minimal speed.

That usually leaves the only option to reduce the number of guns from 8-9 to 6, in order to achieve any significant weight savings, or at least to avoid excessive growth (see the Super Yamatos).

[Borys]

Ahoj!
I'm in the "diminshing returns above 406/420mm camp". The 18 inch has been proven to work, so I'd say that it's the limit to which the game might go.
Would 20" work? Probably yes. But, as in order to ship six of these guns you need a Yamato, is it worthwhile? Wouldn't 12 40-42cm guns, or 8-9 45-46cm guns be better?
Anyway, I set the KKK to stop increasing calibre at 16,5".
Borys

[eltf177]

I feel Logi hit the problem on the head. Yes, larger guns fire larger shells with greater penetration. But larger guns have drawbacks such as:

1) Lower ROF
2) Smaller number of rounds per barrel _or_ need for greater magazine space
3) Range might be longer but unless the weather is good and you have good FC you might not be able to exploit that advantage
4) Increased barrel wear

Not to mention the problems of introducing a new caliber of gun. It's been theorized that Yamato's 18.1-inch guns weren't much better than the US 16-inch gun, especially as the 16-inch gun had a higher ROF backed up with superior FC including gun-laying radar. Eventually you get to the point of diminishing returns.

[ctwaterman]

Lets get a misconception about Rate of Fire out of the way.

When the Flight time of the shell is roughly 60 seconds out beyond 24K yards then Rate of Fire really doesnt come into play.

If you have a rate of fire of 2.5 rounds per 60 seconds and the other ship 2 rounds per 60 seconds guess what your both stuck at 1 round every 60 seconds if you want to adjust for shell splashes.

Charles

[Darman]

Unless you decide to just let fly with as many shells as you can and pray you hit something.  That may become the Egyptian Navy's philosophy... I wonder of Allah would be so gracious as to guide the REN's shells for them.....

[Logi]

I was under the perception that was only the straddle phase of the firing. Once you enter rapid fire (as you've secured their range) you fire at full RoF.

Lets get a misconception about Rate of Fire out of the way.

When the Flight time of the shell is roughly 60 seconds out beyond 24K yards then Rate of Fire really doesnt come into play.

If you have a rate of fire of 2.5 rounds per 60 seconds and the other ship 2 rounds per 60 seconds guess what your both stuck at 1 round every 60 seconds if you want to adjust for shell splashes.

Charles

[ctwaterman]

Not really because the enemy sneaky sucker that he is! is most likely altering his course minutely to throw off your aim you adjust fire after every shot going to rappid fire might have some impact but you are basically adjusting after every single salvo if you can.

At shorter ranges yes the ROF on a Battle Ships guns might actually mean something but beyond 20K yards no it doesnt really matter much unless you getting at least 3 Rounds per minute and nobody that I can remember managed to do that reliabely.

ROF on 14"+ Gun varry between 2 and 2.5 every 60 Seconds or so.  Cycle times usually were between 25 and 35 seconds and not all guns were ready for every salvo.

Charles

[Kaiser Kirk]

I'm kinda with Logi- once brackets indicate range and bearing is found, commence rapid fire until splashes drift off target.   

Wildly dodging shells has a tendency to throw one's own guns off.  After all if your vessel is moving and they are too.. twice as hard.  A sustained change in train is probably ok, but one of the notable features of the late USN BBs was that their guns could maintain their lay in hard turns-

Here's a bit about USN BBs :

The final adjusted rating also reflects the fact that American FC systems employed by far the most advanced stable vertical elements in the world. In practical terms, this meant that American vessels could keep a solution on a target even when performing radical maneuvers. In 1945 test, an American battleship (the North Carolina) was able to maintain a constant solution even when performing back to back high-speed 450-degree turns, followed by back-to-back 100-degree turns.7 This was a much better performance than other contemporary systems, and gave U.S. battleships a major tactical advantage, in that they could both shoot and maneuver, whereas their opponents could only do one or the other.

As for rate of fire, two quotes from Navweaps :
It would seem that with a trained crew, Bismarck was capable of 3 ROF....but didn't use it, though the target change may have effected that.

Many references claim that this was the fastest firing large caliber gun ever built.  The ROF figures listed above represent generally published data that would support that claim.  However, Krupp official documents cite the ROF as being 26 seconds at a four degree elevation, not notably faster than that of other nations' large-caliber weapons.  Note that at this elevation the range would be considerably less than 10,000 meters.  It is possible that well trained gun crews would reduce this time to the 20 seconds necessary to meet a ROF of 3 times per minute.  A May 1941 report by the German Artillerieversuchskommando - AVSK (Artillery Testing Command for Ships) stated that the turret ammunition hoists on Bismarck were capable of delivering between 23 and 25 rounds per minute (for all four turrets), the equivalent of 3 rounds per minute per gun.  However, this same report stated that design faults in the hoists led to two significant breakdowns during the evaluation, both of which caused long interruptions in the ammunition supply.  Finally, it should be noted that Bismarck fired a total of 91 rounds during her thirteen minutes of firing at the Denmark Strait battle, which is actually less than one round per gun per minute.

While Washington, at best could manage ~1.5

4) During her battle with the Japanese battleship Kirishima, USS Washington (BB-56) opened fire at a gun range of 18,500 yards (16,900 m) using radar ranges and optical train and hits were definitely obtained by the third salvo.  In the first part of the battle, Washington fired 42 rounds in approximately 3 minutes (precise time not available) or 1.56 rpmpg.  During the second phase Washington fired 75 rounds in 5 minutes 24 seconds, or 1.54 rpmpg.  Washington fired a total of 117 out of a possible 131 shells, or 89%.  Of the 14 missed salvos, the most notable was the center gun of turret 3 which missed five salvos due to a ball check valve being jarred loose by the the firing shock, causing a loss of hydraulic pressure for that gun.  This loss of pressure prevented the pointer from matching up in the load position.  One other gun had a misfire which caused it to miss two salvos.  The other failures were primarily "error in drill" related.