Dave, doesn`t SoDak`s upper deck does all that as well while still having a much thicker main armour deck than BS? Though the main armour deck is lower placed in BS but even fuzed and decapped shells still reach and penetrate it at shorter ranges than other systems with thicker main decks.Dave Saxton wrote:A spaced array armouring scheme may be able to better deal with a projectile that is difficult to defeat at longer ranges using more conventional techniques, because it can potentially destroy the projectile, render it inert, or otherwise prevent it from penetrating intact. It also introduces fuzing into the equation.
Bismarck against BB-57 South Dakota
Scharnhorst seems not to have benefited from this supposedly superior German radar. In fact, as far as I know the Germans weren't even using the surface search radar with rotating antenna used by allied forces. Didn't the Germans still have to scan for targets using their main fire control array? You seem to be trying to reverse the demonstrated fact that in practice, Allied naval FC was better than what the Germans actually used in their North Sea sorties.Dave Saxton wrote: The German Navy was gaining radar experience years before the Allied navies even had comparable radars in service. The German Navy obtained a lot of war experience in the use of radar during 1939, 1940, and 1941, long before the USN could. Louis Brown the leading expert on WWII radar wrote; that the early war German use of naval radar was much better than the USN's use of radar in the Guadalcanal campaign, that didn't come before mid to late 1942.
With respect to wavelength, the shorter wavelength radars give you better resolution. That's important in distinguishing shell splashes near the target. Also, in my experience sea return is really only a problem close to the transmitting ship. In general, today's x-band FC radars use shorter wavelength than the ones we used in WWII. Lower frequency radars are usually long range air search radars with high power output. You don't need a lot of power when your target is only 20 miles away or less.
Are you actually implying that Bismarck's shells were better able to penetrate S. Dakota's deck than the reverse? Both ships used spaced armor. The later Iowa class added a third spall deck below the main armor deck.Dave Saxton wrote:A spaced array armouring scheme may be able to better deal with a projectile that is difficult to defeat at longer ranges using more conventional techniques, because it can potentially destroy the projectile, render it inert, or otherwise prevent it from penetrating intact. It also introduces fuzing into the equation.
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Dave Saxton
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Lutscha,
Some period US documents refer to the "bomb deck" on the fast battleships as a "yaw deck". That opens up a new possibility as to it's actual purpose, and if it does induce yaw, then there would be little to no reduction in the sum effective thickness caused by using two decks. In other words, with yaw in the equation, the effective thickness is the main deck + the bomb deck. Very good indeed!
The upper deck of 1 1/2" is not thick enough to de-cap large projectiles. The distance between the two decks is also too small for fuzing to occur in most cases.
I have used some cross sectional Tirpitz drawings and studied the possible trajectories, velocities, and the possible distances, travelled by projectiles after penetrating the upper deck or upper belt before they could explode, and the likely striking angle against the panzer deck should they not explode. In cases of angles of fall up to about 37* (IRRC) an active shell will most likely explode before reaching the PD. It will also likely pass through one or more armoured bulkheads before reaching the PD as well. In cases of less than about 30* angle of fall, a shell doesn't have a particulary favorable striking angle against the panzer deck should it reach it. In cases of angles of fall greater than about 35*, it becomes much more problematic that fuzing will occur before the shell reaches the PD with a favorable striking angle, but at those angles of fall (ranges) the shell is going to be very difficult for any system to deal with.
The upper deck and upper belt of the German systems are thick enough to insure fuzing and de-capping of the largest projectiles. When de-capping occurs there is more induced yaw as well. Since a yawed projectile requires more energy to attain penetration, that would compensate for any loss of sum effective thickness possibly caused by using two armoured decks, as in the American case. A de-capped projectile will require more energy to attain penetration as well, and in such case, the energy required may exceed what it can tolerate and still penetrate intact.
Some period US documents refer to the "bomb deck" on the fast battleships as a "yaw deck". That opens up a new possibility as to it's actual purpose, and if it does induce yaw, then there would be little to no reduction in the sum effective thickness caused by using two decks. In other words, with yaw in the equation, the effective thickness is the main deck + the bomb deck. Very good indeed!
The upper deck of 1 1/2" is not thick enough to de-cap large projectiles. The distance between the two decks is also too small for fuzing to occur in most cases.
I have used some cross sectional Tirpitz drawings and studied the possible trajectories, velocities, and the possible distances, travelled by projectiles after penetrating the upper deck or upper belt before they could explode, and the likely striking angle against the panzer deck should they not explode. In cases of angles of fall up to about 37* (IRRC) an active shell will most likely explode before reaching the PD. It will also likely pass through one or more armoured bulkheads before reaching the PD as well. In cases of less than about 30* angle of fall, a shell doesn't have a particulary favorable striking angle against the panzer deck should it reach it. In cases of angles of fall greater than about 35*, it becomes much more problematic that fuzing will occur before the shell reaches the PD with a favorable striking angle, but at those angles of fall (ranges) the shell is going to be very difficult for any system to deal with.
The upper deck and upper belt of the German systems are thick enough to insure fuzing and de-capping of the largest projectiles. When de-capping occurs there is more induced yaw as well. Since a yawed projectile requires more energy to attain penetration, that would compensate for any loss of sum effective thickness possibly caused by using two armoured decks, as in the American case. A de-capped projectile will require more energy to attain penetration as well, and in such case, the energy required may exceed what it can tolerate and still penetrate intact.
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Dave Saxton
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The Hohentwiel used a constantly rotating antenna. The Scharnhorst's forward radars were destroyed by an early hit from the Norfolk, and that changed the whole ballgame. Just plain bad luck.Bgile wrote: Scharnhorst seems not to have benefited from this supposedly superior German radar. In fact, as far as I know the Germans weren't even using the surface search radar with rotating antenna used by allied forces. Didn't the Germans still have to scan for targets using their main fire control array? You seem to be trying to reverse the demonstrated fact that in practice, Allied naval FC was better than what the Germans actually used in their North Sea sorties.....
I have never said that the German radars were superior.
Are you talking about side to side resolution, or resolution for range, and as compared using what?
My mistake. I thought the purpose of your statement about how much earlier the Germans were working on radar was intended to show they were ahead in technology.Dave Saxton wrote:The Hohentwiel used a constantly rotating antenna. The Scharnhorst's forward radars were destroyed by an early hit from the Norfolk, and that changed the whole ballgame. Just plain bad luck.Bgile wrote: Scharnhorst seems not to have benefited from this supposedly superior German radar. In fact, as far as I know the Germans weren't even using the surface search radar with rotating antenna used by allied forces. Didn't the Germans still have to scan for targets using their main fire control array? You seem to be trying to reverse the demonstrated fact that in practice, Allied naval FC was better than what the Germans actually used in their North Sea sorties.....
I have never said that the German radars were superior.
Are you talking about side to side resolution, or resolution for range, and as compared using what?
Are you saying Scharnhorst had a small, rotating surface search radar with a ppi like the sps-10 series, and it got hit at the same time as Scharnhorsts main FC radar on the coupula got hit? Or by a different shell? I haven't heard anything about this.
I was referring to range resolution, comparing X-band radars to S-band and below. For that matter, I think everthing to do with target definition is superior with higher frequencies, all other things being equal.
Generally speaking, air search radars are much larger than surface search radars. This is because they usually use lower frequencies, and that dictates that the antenna be larger due to the relationship between antennal components and the wavelength of the signal.
I'm admittedly a bit hazy about some of this because it was a long time ago, but in the navy I went to radar maintence school and I've stood radar watches and esm watches on a submarine.
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Dave Saxton
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According to Derek Howse (a noted Britsh expert on WWII naval radar and involved with the ASE at the time), Scharnhorst had a Hohentwiel search radar. Frank Rueter also claims this. I find Howse's and Rueter's claims very plausible, because the Tirpitz had been equipped with a Hohentwiel prior to the close of 1943, even though still laid up. The Scharnhorst was recieving the same upgrades as the Tirpitz. Sieche claims that Tirpitz's Hohentwiel antenna was at first mounted just above the FuMO26 antenna on the foretop, but was moved to the foremast shortly after the Scharnhorst's loss.
Range resolution is normally the function of pulse width and/or bandwidth, depending on the type of radar, and how the radar processes the range data. The US S band and X band firecontrol radars used pulse widths much shorter than the 40cm radars, resulting in much improved range resolution by comparison to the 40cm radars. If the particular radar uses MTI, pulse compression, doppler filtering, or other signal processing it will certainly have superior range resolution, but that's the result of the signal processing rather than the frequency.
Wavelength does have an effect on side to side resolution in many cases, because a narrower beam (half power beam width) can be attained without a large (perhaps larger than practical) antenna by using a shorter wave length.
HPBW=(K)WL/D
K is the correction factor for the type of antenna and it's nominal efficiency. It is usually 1.22 with a dish type atennna, but can vary down to 0.72 for a dipole array, and be as high as 1.48 for a wave guide arperture. D is the sum of the dipoles in wave lengths when dealing with a dipole array, or it is the area of the waveguide window or arperture, when dealing with those types of antennas.
Range resolution is normally the function of pulse width and/or bandwidth, depending on the type of radar, and how the radar processes the range data. The US S band and X band firecontrol radars used pulse widths much shorter than the 40cm radars, resulting in much improved range resolution by comparison to the 40cm radars. If the particular radar uses MTI, pulse compression, doppler filtering, or other signal processing it will certainly have superior range resolution, but that's the result of the signal processing rather than the frequency.
Wavelength does have an effect on side to side resolution in many cases, because a narrower beam (half power beam width) can be attained without a large (perhaps larger than practical) antenna by using a shorter wave length.
HPBW=(K)WL/D
K is the correction factor for the type of antenna and it's nominal efficiency. It is usually 1.22 with a dish type atennna, but can vary down to 0.72 for a dipole array, and be as high as 1.48 for a wave guide arperture. D is the sum of the dipoles in wave lengths when dealing with a dipole array, or it is the area of the waveguide window or arperture, when dealing with those types of antennas.
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Dave Saxton
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The standard US base detonating fuzes had a delay of .035-second. The Jean Bart had a heavier armoured deck than Bismarck, being 15cm in thickness and a lower armoured deck of 4cm thickness over the secondary magazines. The arrangement was both opposite of that in Bismarck and the placement of the two protective decks was closer together. In Bismarck the weather deck, which also served as a main structural deck had 5cm armour overall except for above the powder magazines where the thickness was increased to 8cm. The Panzerdeck was located two decks below the weather deck, placing it about the middle of the main belt armour. The thickness of this deck was 8cm except in way of the magazines where the thickness increased to 9,5cm. The inclined, armoured scarps were 11cm in way of the machinery spaces and 12cm in way of the magazines.
The German designers, having to work with a requirement that the ships be able to navigate Germany's shallow coastal waterways, harbours, and inland waterways had to design and construct a ship with relatively shallow draught and of necessity, modest freeboard. At the same time, the ships would have to be stable gun platforms and this precluded placement of a heavy armoured deck high in the ship--i.e., at the top of the main belt as in most contemporaries. Consequently, the designers sought to utilize the defensive properties of the armour deck to reinforce a very modest thickness of belt armour. In choosing a belt thickness of 32cm instead of the heavier 35cm used in the Scharnhorst, weight was saved which could be applied to an upper citadel belt; the Scharnhorsts lacked this heavy citadel armour and this left their Panzerdeck vulnerable at certain ranges at which a shell could enter above the main belt yet still reach the armour deck.
Behind the main and citadel belts, a continuation of the torpedo bulkhead was carried up to the weather deck and was intended to contain splinters and blast from shells which penetrated the side armour.
The philosophy the German designers followed when it came to the placement and thickness of the armour on the weather and Panzer decks, as well as the upper citadel belt, had four objectives:
1. Keep out light to medium common piercing shells
2. Initiate fuze action of AP bombs and shells
3. Strip the piercing caps from armour piercing shells
4. Induce yawing to the shell so as to degrade its performance.
Inititating fuze action, ie, causing the shell to decelerate sufficiently for its inertial slug to slam forward and explode the detonator and fire the delay element, was considered highly important as it was hoped the shell would detonate somewhere in the two levels between the weather deck and the Panzerdeck. The levels between the two armoured decks was considered to be a sacrificial zone and was devoted to various crew spaces and workshops.
Stripping the piercing caps from AP shells was also an important part of the defensive system, as it degraded a shell's ability to penetrate face hardened armour of the Panzerdeck, should a shell reach it.
Finally, all shells are inherently unstable and depend on the rotation provided by the rifling to make them stable in flight. Even so, ideally stabilized shells have a slight amount of yaw or wobble in flight whereby the noze of the shell slightly rotates around the shell axis rather than exactly in sync with it. Stability is a function of shell length, weight distribution, velocity and rifling twist. Assuming the ordnance fellow have done their work properly, a shell or bullet will remain stable over the entirity of its range parameters (from the muzzle to whatever its maximum range is--ie, it will have stable flight characteristics with minimal yaw so long as its combination of x-meters/second of travel + y-rpms/second of rotation does not fall below a certain point. If it does lose enough velocity the shell will begin to yaw badly and perhaps even tumble in flight.
What the Germans were attempting to do was to use the armour of the weather deck to decelerate a shell enough to drop it below the shell's optimum velocity and rate of rotation so that it became unstable and either began to yaw badly or started to tumble. As Dave points out, a badly yawed shell, which has also lost its piercing cap, will have a seriously degraded armour penetrating performance should it reach the Panzerdeck.
In the case of the hit on Jean Bart, the weather deck was 6mm ordinary steel, followed by a second deck of 22mm thickness. Below that was the 15cm armour deck and the 4cm splinter interception deck. It is unlikely the shell was decapped or yawed until hitting the main armour deck, although it is possible the deceleration caused by passing through the two upper decks might have initiated the fuze. While yawing probably developed due to deceleration with the armour deck, the distance between it and the splinter deck was to slight for yawing to become a factor or for the shell to detonate before reaching the magazine.
In any event, the horizontal protection protection schemes of Bismarck and Jean Bart are not directly comparable as the philosophies behind them were radically different.
It is worth noting, that in the case of Bismarck and Tirpitz, the design and layout of the armour protection scheme was not entirely ideal. When originally set down as rough designs, the planned main battery was to have been 33cm guns. This was increased during the final working designs to 35cm, at which time manufacture of the armour began. When Raeder authorized 38cm guns for the main battery, it was too late to alter specifications as the armour was already being manufactured. As a result, the Bismarck class was somewhat underarmoured for the calibre guns it carried in similar fashion to the USN's North Carolina class which had been designed to withstand 14-inch gunfire yet wound up with 16in guns.
One might also consider the horizontal protection a compromise, and while it may have worked well enough against AP shells, had the inherent danger that should the side armour be holed, a list could cause flooding above the low placed armoured deck and a loss of stability if it spread over too great an area. That said, there was little else the German designers could have done since a higher armoured deck would have compromised the initial stability required as a gun platform. A heavier belt would only have been possible at the cost of either speed or fire power, and the naval high command did not consider either of those to be an option.
The German designers, having to work with a requirement that the ships be able to navigate Germany's shallow coastal waterways, harbours, and inland waterways had to design and construct a ship with relatively shallow draught and of necessity, modest freeboard. At the same time, the ships would have to be stable gun platforms and this precluded placement of a heavy armoured deck high in the ship--i.e., at the top of the main belt as in most contemporaries. Consequently, the designers sought to utilize the defensive properties of the armour deck to reinforce a very modest thickness of belt armour. In choosing a belt thickness of 32cm instead of the heavier 35cm used in the Scharnhorst, weight was saved which could be applied to an upper citadel belt; the Scharnhorsts lacked this heavy citadel armour and this left their Panzerdeck vulnerable at certain ranges at which a shell could enter above the main belt yet still reach the armour deck.
Behind the main and citadel belts, a continuation of the torpedo bulkhead was carried up to the weather deck and was intended to contain splinters and blast from shells which penetrated the side armour.
The philosophy the German designers followed when it came to the placement and thickness of the armour on the weather and Panzer decks, as well as the upper citadel belt, had four objectives:
1. Keep out light to medium common piercing shells
2. Initiate fuze action of AP bombs and shells
3. Strip the piercing caps from armour piercing shells
4. Induce yawing to the shell so as to degrade its performance.
Inititating fuze action, ie, causing the shell to decelerate sufficiently for its inertial slug to slam forward and explode the detonator and fire the delay element, was considered highly important as it was hoped the shell would detonate somewhere in the two levels between the weather deck and the Panzerdeck. The levels between the two armoured decks was considered to be a sacrificial zone and was devoted to various crew spaces and workshops.
Stripping the piercing caps from AP shells was also an important part of the defensive system, as it degraded a shell's ability to penetrate face hardened armour of the Panzerdeck, should a shell reach it.
Finally, all shells are inherently unstable and depend on the rotation provided by the rifling to make them stable in flight. Even so, ideally stabilized shells have a slight amount of yaw or wobble in flight whereby the noze of the shell slightly rotates around the shell axis rather than exactly in sync with it. Stability is a function of shell length, weight distribution, velocity and rifling twist. Assuming the ordnance fellow have done their work properly, a shell or bullet will remain stable over the entirity of its range parameters (from the muzzle to whatever its maximum range is--ie, it will have stable flight characteristics with minimal yaw so long as its combination of x-meters/second of travel + y-rpms/second of rotation does not fall below a certain point. If it does lose enough velocity the shell will begin to yaw badly and perhaps even tumble in flight.
What the Germans were attempting to do was to use the armour of the weather deck to decelerate a shell enough to drop it below the shell's optimum velocity and rate of rotation so that it became unstable and either began to yaw badly or started to tumble. As Dave points out, a badly yawed shell, which has also lost its piercing cap, will have a seriously degraded armour penetrating performance should it reach the Panzerdeck.
In the case of the hit on Jean Bart, the weather deck was 6mm ordinary steel, followed by a second deck of 22mm thickness. Below that was the 15cm armour deck and the 4cm splinter interception deck. It is unlikely the shell was decapped or yawed until hitting the main armour deck, although it is possible the deceleration caused by passing through the two upper decks might have initiated the fuze. While yawing probably developed due to deceleration with the armour deck, the distance between it and the splinter deck was to slight for yawing to become a factor or for the shell to detonate before reaching the magazine.
In any event, the horizontal protection protection schemes of Bismarck and Jean Bart are not directly comparable as the philosophies behind them were radically different.
It is worth noting, that in the case of Bismarck and Tirpitz, the design and layout of the armour protection scheme was not entirely ideal. When originally set down as rough designs, the planned main battery was to have been 33cm guns. This was increased during the final working designs to 35cm, at which time manufacture of the armour began. When Raeder authorized 38cm guns for the main battery, it was too late to alter specifications as the armour was already being manufactured. As a result, the Bismarck class was somewhat underarmoured for the calibre guns it carried in similar fashion to the USN's North Carolina class which had been designed to withstand 14-inch gunfire yet wound up with 16in guns.
One might also consider the horizontal protection a compromise, and while it may have worked well enough against AP shells, had the inherent danger that should the side armour be holed, a list could cause flooding above the low placed armoured deck and a loss of stability if it spread over too great an area. That said, there was little else the German designers could have done since a higher armoured deck would have compromised the initial stability required as a gun platform. A heavier belt would only have been possible at the cost of either speed or fire power, and the naval high command did not consider either of those to be an option.
Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.
Tommy,
Thank you for your detailed explanation. It always adds something I don't know about, such as your explanation of the reasoning behind the penetration of Jean Bart's deck protection.
What You and Dave both seem to be saying is that Bismarck's armor scheme was sufficient to stop the 2700 lb AP shell at any range, even though the Germans considered it a compromise. Any thoughts on how much thinner they could have made it and still make Bismarck's citadel impervious to any possible AP shell? I think we can say that the US shell is probably the wost case.
While I certainly understand the logic behind this, I've always thought there were limits to what it would stop. Apparently you guys think it was sufficient against most anything it would reasonable encounter.
Thank you for your detailed explanation. It always adds something I don't know about, such as your explanation of the reasoning behind the penetration of Jean Bart's deck protection.
What You and Dave both seem to be saying is that Bismarck's armor scheme was sufficient to stop the 2700 lb AP shell at any range, even though the Germans considered it a compromise. Any thoughts on how much thinner they could have made it and still make Bismarck's citadel impervious to any possible AP shell? I think we can say that the US shell is probably the wost case.
While I certainly understand the logic behind this, I've always thought there were limits to what it would stop. Apparently you guys think it was sufficient against most anything it would reasonable encounter.
Didn't the british test their 15" shell against Baden, and find that her protection (very similar to Bismarck) didn't keep it from going off below the lower armor deck?
Tommy stated that the Germans used face hardened armor on their main armored deck. Isn't that very unusual? It was sure criticized when the French used it on their turret tops.
The conclusion to be drawn here is that the "all or nothing" scheme was completely wrong, and the tests which caused it to be adopted were flawed. It would have been better to simply scale up WWI schemes like the Germans did.
Tommy stated that the Germans used face hardened armor on their main armored deck. Isn't that very unusual? It was sure criticized when the French used it on their turret tops.
The conclusion to be drawn here is that the "all or nothing" scheme was completely wrong, and the tests which caused it to be adopted were flawed. It would have been better to simply scale up WWI schemes like the Germans did.
That seems to be the case but I don`t think that that`s true because until now I have seen nothing to support such a view. Admittedly I am not searching and wouldn`t be quite apt to I believe.Bgile wrote: While I certainly understand the logic behind this, I've always thought there were limits to what it would stop. Apparently you guys think it was sufficient against most anything it would reasonable encounter.
One Okun related question. Why is he wrong when his program`s result match with German results from the Gkds. 100? Afair he also changed details when presented data by George Elder. That`s why I have trouble to accept, that he is wrong, when his work matches with real live tests.
We don`t know the range at which JB was hit and until I read something new I continue to consider her deck armour as greatly superior to BS` one due to the work of Okun.
So if Okun is wrong, please give us a detailed article about how and why with sources. That would be great.
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Dave Saxton
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I certainly do not believe that Bismarck's protection was up to providing protection vs large projectiles to any range, and I doubt that Thomas holds such a view either.
Primary documents dating from circa 1936 state that the IZ was to be from 20-30km vs 15" projectiles. That is certainly a reasonable specification vs 15" projectiles, but I would not say that it applies to most 16" projectiles. There is bound to be a shrinkage of IZ.
The critical factor is the angle of fall, because as the angle of fall starts to exceed around 30*; the less likely a shell will fuze before reaching the PD, and the eventual striking angle vs the PD becomes much more favorable, (although the shell would still be yawed). The South Dakota 16" reaches 30* angle of fall at about 27,000 yards.
The Panzer Deck was not face hardened armour, it was homogenous Wh, but the PD Wh was harder than the Wh used for the upper deck and other applications. The British found the Tirpitz PD plates to be about 250 brinnel as compared to about 225 brinnel for the upper deck plates. Wh at 250 brinnel has a elongation of ~22% and a tensile strength of about 130 psi. The harder plates would make it tougher on damaged and yawed projectiles. This makes intact penetration less likely when a penetration is likely.
The British found that it took about 10% more energy for their 15" APC shells to penetrate the 100mm Wh Tirpitz plates, than it took to penetrate 4" plates of their own homogenous (NCA) armour. [/i]
Primary documents dating from circa 1936 state that the IZ was to be from 20-30km vs 15" projectiles. That is certainly a reasonable specification vs 15" projectiles, but I would not say that it applies to most 16" projectiles. There is bound to be a shrinkage of IZ.
The critical factor is the angle of fall, because as the angle of fall starts to exceed around 30*; the less likely a shell will fuze before reaching the PD, and the eventual striking angle vs the PD becomes much more favorable, (although the shell would still be yawed). The South Dakota 16" reaches 30* angle of fall at about 27,000 yards.
The Panzer Deck was not face hardened armour, it was homogenous Wh, but the PD Wh was harder than the Wh used for the upper deck and other applications. The British found the Tirpitz PD plates to be about 250 brinnel as compared to about 225 brinnel for the upper deck plates. Wh at 250 brinnel has a elongation of ~22% and a tensile strength of about 130 psi. The harder plates would make it tougher on damaged and yawed projectiles. This makes intact penetration less likely when a penetration is likely.
The British found that it took about 10% more energy for their 15" APC shells to penetrate the 100mm Wh Tirpitz plates, than it took to penetrate 4" plates of their own homogenous (NCA) armour. [/i]