Turret Armor

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Javier L.
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Turret Armor

Post by Javier L. »

Looking at Bismarck's turret armor scheme in this site I was thinking if it wouldn't have been better to place thinner plates in the back and reinforce the front instead. 320 mm as back shield seems a lot to me because shell impacts in the back area of a turret are unlikely to happen unless you are fighting many enemies at the same time. I think a back shield of 220 mm would have been more reasonable. Then 100 mm more in thickness would have been available for the front plates (in my opinion the 180 mm sloped front plate is too thin and needed to be reinforced). Unless this change of weights affected the balance of the turret I believe it would have been a better choice. Any comments?

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Tiornu
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Re: Turret Armor

Post by Tiornu »

It was common in many battleships to have very thick back plates, not for protection, but to counter-balance heavy weights at the front of the turret--the guns, trunnions, etc.
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Re: Turret Armor

Post by Paul L »

Tiornu wrote:It was common in many battleships to have very thick back plates, not for protection, but to counter-balance heavy weights at the front of the turret--the guns, trunnions, etc.
Since I read Dr Elders paper on spaced armor , I always assumed WW-II ships had spaced armor. I think that the side plan views of the hulls suggests various bulk heads as anti torpedo screens? But since spaced armor was known about since 1906 [italian battleship?], why was it not common place in such an advanced design as the Bismarck and its turrets.
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Re: Turret Armor

Post by Tiornu »

Spaced arrays tend to be less effective than single plates of the same total thickness. It would be difficult to get enough spacing in a turret system anyway.
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George Elder

Post by George Elder »

Rich is correct in noting that it would be very difficult to work a spaced array into the typical confines of a BB turret given all that is contained within. However, the claim that spaced "arrays tend to be less effective than single plates of the same total thickness" is very problematic. In terms of AP shells, most studies show spaced arrays are actually more effective in inducing shell shatter in caliber=plate thickness projectiles that are traveling at their CV than is a single plate. Moreover, this tendency to achive shatter increases as velocity goes up. Thus, at a velocity/range wherein a projectile can penetrate a single plate intact, which is a very bad thing, the projectile will most likily be shattered vs a spaced array. Of course, a supplementary splinter blate behind the spaced array absorbs the resultant splinters, wherein such a splinter plate behind a single layer system will accord little protection against an intact projectile. Some of these issues were addressed by Pugliese, and the Italian trails are what convinced him to use a spaced array. The Germans, who also conducted a lot of work in spaced arrays, came to to similar conclusions as did the Italiams, although the weight of such systems was deemed unacceptable to them. They went their own way in employing a multi-layer system, but that is another story.

George
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Re: George Elder

Post by Paul L »

George Elder wrote:Rich is correct in noting that it would be very difficult to work a spaced array into the typical confines of a BB turret given all that is contained within. However, the claim that spaced "arrays tend to be less effective than single plates of the same total thickness" is very problematic. In terms of AP shells, most studies show spaced arrays are actually more effective in inducing shell shatter in caliber=plate thickness projectiles that are traveling at their CV than is a single plate. Moreover, this tendency to achive shatter increases as velocity goes up. Thus, at a velocity/range wherein a projectile can penetrate a single plate intact, which is a very bad thing, the projectile will most likily be shattered vs a spaced array. Of course, a supplementary splinter blate behind the spaced array absorbs the resultant splinters, wherein such a splinter plate behind a single layer system will accord little protection against an intact projectile. Some of these issues were addressed by Pugliese, and the Italian trails are what convinced him to use a spaced array. The Germans, who also conducted a lot of work in spaced arrays, came to to similar conclusions as did the Italiams, although the weight of such systems was deemed unacceptable to them. They went their own way in employing a multi-layer system, but that is another story.

George
Sounds good to me! I have toyed with a simplistic formula involving spaced armor effects. It seems to work well with smaller projectiles & APFSDS.

The net additional resistance of a given spaced plate is t/d [spaced plate] ^0.5 * Penetrator velocity at impact. Plate hardness would increase this spaced plate effectiveness by ~ 1.25 -1.34 for SHS or VHS/FH

So a 16 inch AP round striking a 3 inch FH spaced plate becomes
0.25^0.5*0.5 = 0.25 diameter additional resistance or LOS + 4 inches.

if the same array is struck by say a 14 inch shell, the resistance is
0.29^0.5*0.5 = 0.27 diameter additional resistance or LOS + 3.75 inches.

If the same array is struck by a 12 inch shell,the resistance is
0.33^0.5*0.5 = 0.29 diameter additional resistance or LOS + 3.46 inches.

This doesn't address the possibility of shell exploding inbetween spaced plate and main plate , or the amount that the ballistic cap affects the above figures?
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Well...

Post by George Elder »

I would like to see the data base you use. One must also recognize that the value of spaced arrays declines as a shell's velocity decreases below its CV, or critical velocity. Below this figure, the shell is unlikily to break up, and thus factors such is general shear resistance assume assendence. However, here we also find fuzing is a greater consideration because the shell is traveling more slowely. Thus, the real question concerns an intact projectile's detonation prior to encountering the internal plinter bulkhead. Lots of room for exploration here. Of course, one can also play with the geomertry of the external and internal plates, and thus harvest the rewards of obliquity effects, yaw generation, etc.. But modeling these effects is difficult, as Goldsmith plainly shows. Overall, we must have a good data base to confirm any general approaches toward caculating the relative effectiveness of spaced arrays vs single plate systems -- and I'm not sure an adequate data base exists. This could lead to an interesting search!

George
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Spaced arrays

Post by Bill Jurens »

As Tiornu (and some others) have pointed out, proving ground testing between and after the wars, (which includes literally hundreds of tests) quite consistently showed that spaced-array configurations were, overall, somewhat less efficient than single plates. This is, in fact, one reason why spaced arrays and all of the associated 'sacrificial zone' business -- if the latter ever existed at all -- was abandoned between the wars and replaced, almost universally, by all or nothing configurations. In that regard, in general one might conclude that "spaced array thinking" on the part of designers was representative of regressive rather than progressive thinking, at least so far as ships were concerned. (A Google search on the "Sacrificial Zone" concept, by the way, would seem to indicate that it springs from muddle-headed thinking by inexperienced modern revisionists.)

I think, but am by no means certain, that much of the confusion here stems from the wide-spread adoption of skirting plates and similar laminated arrangments to armored fighting vehicles during WWII. These were, however, primarily intended to defeat shaped-charge weapons, with the associated loss of efficiency in defeating standard capped a.p. projectiles being recieved as an acceptable compromise. Many people have, I think, assumed that what's sauce for the goose, e.g. tanks, is sauce for the gander, i.e. battleships. This is not the case.

It is very common to find modern students of these subjects attempting to superimpose knowledge and experience stemming from armored fighting vehicles on to armored ships. (This is especially true because experience in AFV shooting is much more common.) Unfortunately, for a variety of reasons having to do both with exterior and terminal ballistics, the two situations are really far from congruent, and extrapolation from one to the other -- especially by those not well-based in the subjects -- is almost always inaccurate or misleading.

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George Elder

Post by George Elder »

Hi Bill:

Then how do explain away the contrary data -- including the findings of Pugliese, the Krupp Naval spaced array trials, etc.?

George
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Post by Paul L »

All due respects Bill but you need to go back to school. Schutzen skirts were designed to defeat Soviet 14.5mm HVAP shot from the AT rifles...shaped charges were only in their infancy at that time and it was not connected until after the war. Poor american historical analyasis is responsible for this many mistakes.If fact Against a large caliber round like a Panzer faust the increased standoff would probably increase the penetration not reduce it...although I'm still waiting on Panzer faust standoff penetration charts to confirm that. At least it would not offer much protection.

Germans never even tested against shaped charge they tested against AP and HE rounds.

They defeat these projectiles cause they are hard and brittle and the aysemetrical impact conditions result in lateral forces that exceed the projectiles strenght thus resulting in whole sale shattering of the penetrator. In tests they these penetrators didn't even scratch the base armor.

With reguards to APC impacts of spaced armor the softer ballistic cap absorbs the impact on the spaced plate preventing the erosion shattering stresses from reaching the main hard brittle penetrator. Against unprotected shells it should have sufficent effect as outlined before. Also their is the question of exploding shells. The soviets never recognised this problem and had their APHE shells exploding between plates. Soviets sources have related that even 122mm APHE would detonate between the Pz-III Vor panser sheet and the main armor.

Application of the above mentioned perforated plates would have been sufficent to disloge the ballistic cap and shatter the main penetrator to some degree and possible detonate the shell. Certainly two plates would have worked. The outer perforated plate could have been installed as an applique and doesn't have to be that thick to work.
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This is what the data I have indicates...

Post by George Elder »

Hi Paul:

Your review of the historical record is interesting. I was not aware of some of the historical details you broach, and find them interesting. With regard to naval applicationa, the British gave up on spaced arrays in about 1920, although as early as 1908 the Italians had noted the shatter effects against caliber sized shells traveling at CV that are mentioned above. They and the Germans did a lot of research here. As for the German skirting plates, I had little information on the R&D leading up to their use, and I would be most thankful for any info you have on this subject. I am aware of the US 90 mm shell data supporting your shatter notion, and how these results certainly surprised the reviewers. Yes, that's a neat study. Incidently, I presume some of relative effectiveness relationships you have been working on in single plate vs divided armor are based on the Goldsmith piece. I may be mistaken. It is a bit of monster to go through, and it's heavy reading. This is an interesting topic.

George
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Penetration tests, etc.

Post by Bill Jurens »

Glad to be corrected regarding the application of spaced armor to armored fighting vehicles, which are admittedly not my specialty. I take it then that spaced armor was actually quite common in tanks, etc. even before WWII and the advent of shaped charges. It would seem unlikely that such an obvious and easily implimented protective strategy -- had it worked on regular tanks prior to that time -- would not have seen widespread application well before World War II. Even then, the appearance of spaced arrays seems to have been limited to things like tracks and wheels, etc, with single thickness plating used on turrets and faceplates. Again, this is not my specialty, so please tell me more.

So far as thick naval armor is concerned, experimental testing sometimes showed that the application of thin plates in front of thicker plates did indeed reduce overall penetration, but these were unusual situations. These occasional positive results often initiated a storm of further research, which usually fairly quickly died out when it was discovered that the positive results were essentially aberrant, and that overall, resistance was usually decreased. It would be wrong to claim that spaced armor NEVER improved penetration, but it is fair to note that the general findings were that single plates were in general quite a bit superior to armor arrays of equal thickness.

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You have the Pugliese material...

Post by George Elder »

The Italians based their scheme on what certainly appears to be a dedicated R&D program that wasn't seeking odd-ball results. Not only that, at the time, the shear issue was addressed, and the proving ground tests allayed that concern according to Pugliese. I have searched hard to find dedicated R&D programs that addressed spaced array research after the British dropped out of the game in circa 1920. The only efforts I can find are the Italian and German programs. The Russians dabbled with the idea in some WWI designs, IIRC, but I do not see signs of an extensive R&D program in this area prior to the 1940s except in Germany and Italy. However, I strongly suspect some research was going on in the US given the reference we find to using weather deck armor for yaw induction. As for tank research, Paul, Neil, etc., know that history far better than myself. I'm not sure, however, that spaced arrays for AFV purposes were in the works in many countries prior to to WWII due to -- available space concerns.

George
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Re: Penetration tests, etc.

Post by Tiornu »

The Italians appear to have been concerned about why their test results differed from those of the other navies, but I have never heard whether they found the variable or if it was simply a glitch in their testing. They used spaced armor even when the spacing was inadequate for letting the cap separate from the shell body.
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No, the Italians considered...

Post by George Elder »

... the results of early contray tests, but their ongoing spaced array testing program's results proved robust -- some of which we have. They tested at several scales, going up to 1-to-1, a test D&G refer to. We have extensive data on the 203 mm & 320 mm test, but there were also tests done with smaller versions. In this case, the focus was two-fold, as in measuring the aerray's resistance against caliber sized attacks and to see if HE shells could compromise the spaced array's structure, which does not seem to have been the case. Here is a test I am sure you know about:

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The Production of Ship Armor in Italy
British Intelligence Objectives Sub-Committee
Appendix No11
Spaced Armour
Translated from Italian

About 1934, when the battleships of the Cavour class were being re-modernized, the Admiralty, for the first time, gave consideration to the question of sub-dividing the vertical protection of ships and, in particular, its distribution between two plates, the first of which had the function of decapping the shell and the second - a cemented plate - that of stopping it.
In the first exploratory tests (as a result of which it was decided to provide similar protection for battleships of the VITTORIO VENETO class, also) it was decided, either through lack of time or because of the cost of the experiments, to confine the investigation to determining the minimum thickness of the first plate which would ensure decapping of the shell. No special tests were carried out to determine what distance should separate the two plates in view of the decisive part played in this matter by constructive factors of a totally different kind [note: this is not quite the case, as other documents prove].
The account which follows is a copy of a report on the firing tests carried out in 1935 on a structure composed of two spaced plates representing an element of the armour of battleships of the VITTORIO VENETO class. These tests were carried out with the object indicated above and the tests show clearly what information it was possible to obtain towards a solution of the problem under consideration.

Firing Trials against an Experimental Structure for the side Protection of Battleships LITTORIO and VITTORIO VENETO carried out on 3 April 1935.

Copy for Col. Binghinotto. 29 May 1946

1. The Structure

The structure consisted of a 71[mm] AOD decapping plate mounted on a 10mm plate, spaced at a distance of 200mm from a 225[mm] KC plate mounted on 10mm plate with 50mm thick wooden buffer interposed. Above, below, and at the sides, the cemented plate was let into a 60mm plate. The 71[mm] AOD plate was let into the same perimeter plates except at the lower edge. A suitable network of 15mm flat iron bar was used to separate the cemented plate and backing plate from the decapping plate.

2 . Projectile used

a. GC Terni capped shot, weighing 519Kg [presume 320mm].

b. 203/55 caliber shell, explosive charge with compressed Trinitrotoluene and primed with TUR detonator with fixed delay fuse and ogive modified for the firing range.

3. Angle of Attack and corresponding conditions.

The structure was placed for an angle of attack of 30 deg from the normal for the GC gun and of 33 deg for the 203[mm]. The striking velocity of 538m/sec of the GC shot took into account the angle of fall of about 13 deg and of the inclination of the side of 12 deg corresponding to an inclination of the ship with respect to the plane of fire of 18deg 20min at a combat distance of 16000 meters. The striking velocity of 700m/sec of the 203[mm] explosive shell was necessary in order to make absolutely certain of the activation of the fuse which occurs only at velocities above 600m/sec.

4. Results of tests.

A. Firing tests with GC shot

The shot used was Terni 6601 A.T.II [AT2]. Velocity 537.6 [m/sec]. After being decapped by the 71[mm] AOD plate, in which it produced a hole 390 x 325mm, co-ordinates 1330mm from bottom and 2810mm from left, the shot made a hole 210 x 305mm in the 225[mm] KC plate, flaked zone 480 x 430mm, dish 400 x 60mm and co-ordinates 2950 from left and 960mm from top. The backing plate showed a gash 1000mm x 1090mm. The two bolts immediately above and below the point of attack were cut off and fell in the plane of the target. The shell broke about half way along [its length] and remained fixed in the KC plate with its base almost level with the internal face of the decapping plate. Pieces of the plug and of the ogive of the shell were recovered from the butt about 15m behind the target. The internal portion projecting from the body of the projectile showed a large gash at its summit.

Effect of Fire on the Structure.

As a result of the impact the 71[mm] AOD plate suffered deformation on the right hand side outwards from the upper joint for almost its entire length. The 60mm plate enclosing the right side was completely broken away from the 225 KC plate whilst the external rabette of the joint of the decapping plate was broken off along its entire length. On the left side, the coupling screws joining the 225 KC plate to the 60mm plate were found broken.

B. Firing Tests with 203 explosive shell.

Velocity = 723m/sec. The shell exploded normally causing an impression in the 71 AOD plate 690mm in diameter and 190mm deep with a vertical crack 480mm long and 10mm wide. Co-ordinates for point of attack were 1140 from left and 1400 from the bottom.

Effect of explosion on the structure.

The outer rabette of the left vertical joint of the decapping plate was broken off along its entire length.

5. Conclusions

The type of structure tested is shown to be fully efficient against large caliber shot and against the largest explosive shell expected. From attack with large caliber shot, from similar and even more severe tests with 152 type shot, and the fact that GC shot (50kg) is decapped by 100[mm] KC plate, it has been shown that much higher striking velocities at which the projectiles are broken, will merely increase the residual energy of the plug and pieces of projectiles and that these will be stopped by the splinter screening backing-plate.
A sample of the 60mm plates forming the lateral joining between the cemented and decapping plates is to be sent to Maricosi La Spezia for a determination of its mechanical properties, particularly the impact values from which it may be possible to explain the unsatisfactory behavior [sic] of the perimeter joints of the decapping plate.

[END]

In addition to [the] above comment elsewhere in [the] report [it] says:

Report supplied by San Martino

Italian Navy had not evolved a shell design that was 100% successful against spaced armour.

An 8in shell seen on range at Spezia seemed to have cap fitted lower down shell body than is our [UK] usual practice.

Italian thoughts appeared on similar lines to German for defeat of spaced armour.

General conversation with Italian technicians appeared to indicate that they thought more important function of decap plate was to cause shell to yaw rather than to decap.

Efforts to find later test data failed but Martino said that little or no experimental work on spaced armour had been carried out after the above.

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