General question about BB turrets firing.

[baggers]

Hello.

I just saw theses interresing videos about firing operations of a 16" gun in a 3-guns turrets of a BB:

www.youtube.com/watch?v=Dg-cNmLRgiU

www.youtube.com/watch?v=dVvEPTYrcXA

And have a question:

It is better for accuracy/recoil stress purposes to fire each gun of a tree-gun turrets one after the other, or all at once? Or maybe it exist differents procedures for different purposes?

[galagagalaxian]

That is a complex question to answer, rather than answer in my own clumsy words Here is a good article about Naval Gunnery. And here is an excerpt from it specifically about firing a turret's guns in sequence or unison.

Salvos could be fired as full salvos, where all guns were discharged more or less simultaneously, as partial salvos, where half the main battery (usually either the forward after group) fired together, or as split salvos, where one gun of each turret fired together. Each system had its own advantages and disadvantages. Full salvos looked spectacular, but resulted in relatively large patterns which were difficult to spot and which arrived at relatively long intervals, thus making corrections difficult. Partial salvos reduced the pattern size, made spotting easier, and meant that corrections could be made (on the average) twice as often. Split salvos, due to the extreme separation of the guns, lead to the greatest accuracy and, theoretically, to the highest rate of fire as the director could fire as soon as any arbitrarily selected number of guns was ready to shoot.13



The Navy started experimenting with delay coils - simple mechanisms which prevented adjacent guns from discharging absolutely simultaneously - about 1935. Prior to the installation of delay coils, shells fired in salvo could travel in such a tight formation that they could actually collide, or "kiss" in flight, a phenomena which could be occasionally observed through binoculars. The velocity difference between projectiles traveling in salvo was so small - often less than ten feet per second - that shells fired very slightly late, and perhaps traveling very slightly faster than their counterparts, could spend a considerable amount of time in the confused air stirred up by the leading shells in the group. This increased their drag and made them fall short. An associated problem was that shells were often disturbed by the muzzle blast of an adjacent gun, especially if the muzzles were close together. The resultant wobble also increased the drag. The net result was a considerable number of "wild-shorts," i.e., shells which fell far enough short to be completely out of the pattern.14 Early installations of delay coils, which fired all guns at different times, created problems with turret whip, a problem which was, incidentally, rediscovered in the 1980s when Iowa and her sisters installed similar delays in order to decrease the effects of muzzle blast on pressure-sensitive equipment. Later installations fired both outside guns of a triple turret simultaneously in order to negate, or at least minimize, the effects of whip. The problem was, of course, inherently incurable in twin mounts, which is one reason that it was never used in 5"/38s.

[baggers]

Thanks! It's really a interressing - and funny to read! - article.

I especially like the 6)

The use of a towed target train sometimes posed laughable difficulties. In one case a large caliber projectile cut the towline early in the exercise and the target train slowed rapidly to a stop. The result was complete confusion in the battle line. Some ships took no account of the problem at all, their salvos continuing a majestic march into completely empty ocean (some suspected that this was because they were actually tracking the towing ship instead). Other ships adjusted their fire to remain on the slowing target train, but got hopelessly confused as the targets closed up on each other and began to overlap. The net result was utter chaos, followed by a lengthy argument about exactly how the practice should be scored. Clearly, disrupting an enemy battle line could cause as many problems as it solved.

So, no vertical stabilisation of naval gunnery before the 1930s. But optical "bull's eye" around the roll and pitch of the boat at sea, trying to hit the "firing" button when the target show itself behing the crosshair. God! ^^ I better understand the "accuracy" of naval gunfire now ^^

I noticed that the reliability of guns/turrets is not very good too, even when the target don't fire back!

The reliability of the guns always appears to have varied markedly from ship to ship. In 1942, USS Idaho undertook an exercise deliberately designed to determine ". . . the ability of battleships to maintain an adequate rate of fire under conditions simulating a protracted engagement," expending 597 rounds in 156 salvos. The average salvo interval was 1 minute, 24 seconds, but only 20 of these were full six-gun salvos; the average was 3.82.

So, for my question, I assume full salvos was "standard" before the delay coils.

[galagagalaxian]

Aug 29, 2015 20:58:37 GMT -6 baggers said:

So, no vertical stabilisation of naval gunnery before the 1930s. But optical "bull's eye" around the roll and pitch of the boat at sea, trying to hit the "firing" button when the target show itself behing the crosshair. God! ^^ I better understand the "accuracy" of naval gunfire now ^^

I noticed that the reliability of guns/turrets is not very good too, even when the target don't fire back!

Actually by WW1 most ships had what Rule the Waves would call Director or Improved Director fire tables, where a rather impressive mechanical computer is doing a lot of the measurements. Sufficiently advanced models (Improved or Advanced perhaps in RtW terms) could actually control the firing of the guns electronically. Basically the turret crew would signal the turret is read to fire, then the Fire control team would flip the "fire" switch, the fire control computer would then wait for the ship's pitch and roll to be correct for the positioning of the turrets before triggering the firing of the guns. 

These mechanical computers were really amazing marvels of engineering. If you're curious, here is a 40 minute US Navy training video from 1953 going over the components and working of a late-WW2 era fire control computer.

[baggers]

This roll me bach to school! ^^ Thanks. I alway liked these mechanism. Some of them seem familiars...

Sufficiently advanced models (Improved or Advanced perhaps in RtW terms) could actually control the firing of the guns electronically. Basically the turret crew would signal the turret is read to fire, then the Fire control team would flip the "fire" switch, the fire control computer would then wait for the ship's pitch and roll to be correct for the positioning of the turrets before triggering the firing of the guns.

Are you sure of that?

For having the fire control computer trigger the gun at the correct pitch/roll position, you will need an accurate pitch/roll instant mesure device input for the computer.

And if you have that pitch/roll instant mesure device, you have probably all you need for a vertical stabilisation mechanism instead?

[galagagalaxian]

I admit, I could be wrong. But some kind of gyro mechanism attached to the computer to measure pitch/roll is a lot simpler/cheaper than a complex series of automated machinery to move the turret(s) in real time. Sadly, I can't find a good reference in a quick search.

I found this which I believe describes the method somewhat in the first few pages, but due to the lateness of the hour where I live I am having difficulty parsing it (I was never very good at such dry technical material).

[baggers]

Aug 29, 2015 23:34:58 GMT -6 galagagalaxian said:

I admit, I could be wrong. But some kind of gyro mechanism attached to the computer to measure pitch/roll is a lot simpler/cheaper than a complex series of automated machinery to move the turret(s) in real time. Sadly, I can't find a good reference in a quick search.

I found this which I believe describes the method somewhat in the first few pages, but due to the lateness of the hour where I live I am having difficulty parsing it (I was never very good at such dry technical material).

This is exactly what I'm looking for and answer my last question.

- In "Director firing", nothing is stabilized, and the Firing officier must hit the "fire" button when the target pass behind his optics crosshair, and must take into account the small delay between hitting the button and actual gun firing: "forecasting" is in the hands/eye coordination/anticipation of the officier.

- In "Gyro Director": the optical sights are verticaly stabilized, and the computer delay the firing order until the pitch/rool mesure of the guns match with the stabilizeds optics, and take care of the forecasting too (the forecasting can be manually setted or automatically geared: in any case, The firing officier just aim at the targets with stabilised optics, and hit button.)

- In "Stabilized guns/turets" (not depicted in the pdf) , both optics and guns should be stabilized and synchronised, so forecasting don't matter.

[Fredrik W]

Aug 29, 2015 20:58:37 GMT -6 baggers said:

So, for my question, I assume full salvos was "standard" before the delay coils.

During WW1 most navies fired one gun per turret while the other was reloading. This can be seen in my signature pic, where the König at the battle of Jutland has one gun elevated in firing position and one horizontal in the loading position. According to Friedman, the AH navy fired one gun per turret in their triple turrets.

Edit: It can almost be seen. The original is clearer.

[baggers]

Thanks!

If I want to go even further: what's the intervalle between gunfires of the same turret? A pair of seconds? Without at least a "gyro director", the intervalle between shoots is set by the director taking visually into account pitch/roll for shooting each gun at the same elevation: on top of wave ^^



I also noticed about "gyro director" that some navies (the Japan for example) seems to doesn't have one even at the begining of WW2! I'm curious if in WW1 some boat were equipped, after all...

(side note: a bit modern image, but I find it instinctive about "what's a stabilised optic"^^:

[Fredrik W]

Aug 30, 2015 16:05:48 GMT -6 baggers said:

Thanks!

If I want to go even further: what's the intervalle between gunfires of the same turret? A pair of seconds? Without at least a "gyro director", the intervalle between shoots is set by the director taking visually into account pitch/roll for shooting each gun at the same elevation: on top of wave ^^

Real sustained rate of fire was in practice seldom more than one round per gun per minute for heavy guns, and often less. This is in marked contrast to the theoretical technical ROF given in various gun data tables, which many people take as gospel.

A lot of factors influence the real ROF like visibility, need to observe and correct fire, sea state etc. Then there are rather frequent mechanical failures where one gun will miss a couple of salvoes before fixing the problem.

[baggers]

Thanks! I noticed previously this:

The reliability of the guns always appears to have varied markedly from ship to ship. In 1942, USS Idaho undertook an exercise deliberately designed to determine ". . . the ability of battleships to maintain an adequate rate of fire under conditions simulating a protracted engagement," expending 597 rounds in 156 salvos. The average salvo interval was 1 minute, 24 seconds, but only 20 of these were full six-gun salvos; the average was 3.82.

But I was talking about a "split salvio" like the "König" ones, and my question is about the interval between the "splits", more than the interval between the "salvios".

I imagine something like:

"left gun of each turret fire" - 3s wait for roll back in line with target - "right gun of each turret fire" - 3s wait for roll back in line with target - "middle gun of each turret fire" -> wait 1 minute for guns reloaded/ back in action.

And so on.

[elouda]

Aug 30, 2015 23:59:28 GMT -6 baggers said:

Thanks! I noticed previously this:

The reliability of the guns always appears to have varied markedly from ship to ship. In 1942, USS Idaho undertook an exercise deliberately designed to determine ". . . the ability of battleships to maintain an adequate rate of fire under conditions simulating a protracted engagement," expending 597 rounds in 156 salvos. The average salvo interval was 1 minute, 24 seconds, but only 20 of these were full six-gun salvos; the average was 3.82.

But I was talking about a "split salvio" like the "König" ones, and my question is about the interval between the "splits", more than the interval between the "salvios".

I imagine something like:

"left gun of each turret fire" - 3s wait for roll back in line with target - "right gun of each turret fire" - 3s wait for roll back in line with target - "middle gun of each turret fire" -> wait 1 minute for guns reloaded/ back in action.

And so on.

Most likely one would wait for the half/split salvo to land and corrections to be made before firing the other half. Once on target a decision might be made to fire the follow up as soon as ready.

If you're talking about individual guns, then 3s seems a long time. In principle you'd want atleast 3 shells fired near simultaneously to get a good pattern to correct from, so when firing a split salvo presumably all of the guns in that salvo would fire as close together as possible (might be some hundredths of a second difference due to different distance of turrets from director).

With the 'one gun from each turret' kind of split salvos from large caliber weapons, the issue with turret whip probably isnt a major factor either as due to the long reload cycle, the turret has time to stabilize before the next half (in probably 20-40 seconds).

[thecarthaginian]

Even when the guns fired 'at the same time' they didn't.
The South Dakota and Iowa I know - from having one of the former, specifically the Alabama, quite literally in my back yard - had a firing delay. To lower dispersion from muzzle effects, there was a delay of tenths or hundredths of second in the firing of the guns within the same turret.

[baggers]

Aug 31, 2015 16:07:09 GMT -6 thecarthaginian said:

Even when the guns fired 'at the same time' they didn't.
The South Dakota and Iowa I know - from having one of the former, specifically the Alabama, quite literally in my back yard - had a firing delay. To lower dispersion from muzzle effects, there was a delay of tenths or hundredths of second in the firing of the guns within the same turret.

If i'm not mistaken, you're talking about the "delay coils", and it's a bit too late for RTW:

The Navy started experimenting with delay coils - simple mechanisms which prevented adjacent guns from discharging absolutely simultaneously - about 1935. Prior to the installation of delay coils, shells fired in salvo could travel in such a tight formation that they could actually collide, or "kiss" in flight, a phenomena which could be occasionally observed through binoculars. The velocity difference between projectiles traveling in salvo was so small - often less than ten feet per second - that shells fired very slightly late, and perhaps traveling very slightly faster than their counterparts, could spend a considerable amount of time in the confused air stirred up by the leading shells in the group. This increased their drag and made them fall short. An associated problem was that shells were often disturbed by the muzzle blast of an adjacent gun, especially if the muzzles were close together. The resultant wobble also increased the drag. The net result was a considerable number of "wild-shorts," i.e., shells which fell far enough short to be completely out of the pattern.14 Early installations of delay coils, which fired all guns at different times, created problems with turret whip, a problem which was, incidentally, rediscovered in the 1980s when Iowa and her sisters installed similar delays in order to decrease the effects of muzzle blast on pressure-sensitive equipment. Later installations fired both outside guns of a triple turret simultaneously in order to negate, or at least minimize, the effects of whip. The problem was, of course, inherently incurable in twin mounts, which is one reason that it was never used in 5"/38s.