Bill Jurens wrote: Bismarck would have achieved an obliquity of zero degrees against an Iowa class Class "B" faceplate at a range of about 32000 meters. At that range, the striking velocity is about 460 m/s, i.e. about 1509 f/s. The Navy ballistic limit for the plate for zero degree obliquity assuming a fairly good USN projectile would have been about 579 m/s, i.e. about 1.2 times the striking velocity of the bullet. So complete effective penetration is improbable.
Somebody correct me If I'm wrong but from 32,000 meters not even Yamato's AP shells could penetrate Iowa's turret faces. From 30,000 meters the striking velocity of Yamato's AP shells is 475 m/s.
Bill Jurens wrote:If 579 m/s is required to penetrate at zero degrees, what happens if Bismarck's projectile hits at that velocity? A 579 m/s striking velocity corresponds to a range of about 12500 meters and an angle of fall of 8 degrees. Assuming a 35 degree slope on the plate, this leave a residual obliquity of 27 degrees, and ORD SK 78841 gives a required velocity of 693 m/s to penetrate effectively, again about 1.2 times the actual striking velocity that is experienced.
A 579 m/s striking velocity actually corresponds to a range of about 14,000 meters and an angle of fall of about 10º, unless I made a mistake reading GKDos 100. It doesn't change much but I just though I should mention it. Now, if the 579 m/s figure is correct then we find that in theory Yamato's shells have trouble penetrating Iowa's faces as well. A 579 m/s striking velocity corresponds to a range below 15,000 meters and an angle of fall of about 8.5º. I'm not familiar with "ORD SK 78841" but could someone check Yamato's figures for us?
thanks for your replies, they are most technical and, at the same time, very clear containing no ambiguities. It seems, so, that the 15" Bismarck´s guns would never fully penetrate Iowa´s armour at any given range.
This settles for once and for all, in great part, a discussion that has been quite long.
But, now, we are quite clear that Bismarck couldn´t damage an Iowa best protected zones. Is it there any firing pattern that may affect seriosly an Iowa if engaged by Bismarck?
And:
Jose Rico:
Somebody correct me If I'm wrong but from 32,000 meters not even Yamato's AP shells could penetrate Iowa's turret faces. From 30,000 meters the striking velocity of Yamato's AP shells is 475 m/s.
In what I´m interested is the following: this same criteria can be applied to the Iowa hits on Yamato: did Yamato armour simply reject them?
Best regards.
An appeaser is one who feeds a crocodile, hoping it will eat him last. Sir Winston Churchill
Much depends on the estimate for effective thickness. Should the thick homogenous plates be dinged 2%, 5%, 10%, or 15% for large grain size in the center of the plate? I think it should, but I don't know to what degree? I will have to look up to what degree the BoO found the interior portions of thick Class B plates resulted in lower limit velocities.
I'm finding the homogenous predictions for penetration fall short of predictions for face hardened armour. For example striking at 460 mps at nearly right angles the amount of homogenous armour penetrated (my curves included) is predicted to be about 13% less than the curves for face hardened armour. Could this be so? I'm very suspisious of the calculators and curves for homogenous armour extrapolated out to such thickness.
"I'm finding the homogenous predictions for penetration fall short of predictions for face hardened armour. For example striking at 460 mps at nearly right angles the amount of homogenous armour penetrated (my curves included) is predicted to be about 13% less than the curves for face hardened armour. Could this be so? I'm very suspisious of the calculators and curves for homogenous armour extrapolated out to such thickness."
In the thicker guages one actually does find that the resistance of homogeneous armor is superior to that of face-hardened armor at low obliquities, i.e. near-normal impacts. That is (probably) one reason that the Iowa Class retained homogeneous turret face plates even after the U.S. had perfected the technology to make Class "A" armor in the very heaviest thicknesses.
thanks for your replies, they are most technical and, at the same time, very clear containing no ambiguities. It seems, so, that the 15" Bismarck´s guns would never fully penetrate Iowa´s armour at any given range.
This settles for once and for all, in great part, a discussion that has been quite long.
But, now, we are quite clear that Bismarck couldn´t damage an Iowa best protected zones. Is it there any firing pattern that may affect seriosly an Iowa if engaged by Bismarck?
Best regards.
I think it’s quite reasonable to rank the IOWA class right in the next tear below the YAMATO class in terms resistance to gunfire to the citadel. One might argue that they are a bit under protected for their displacement and didn’t meet their designed protection criterion but to be fair most foreign battleships didn’t either. In terms of vertical armor, the IOWAs are ‘immune’ to the 38cm L/4.4 down to about 23,500yds or so (belt and barbette armor) at 90° on an even keel. There are drawbacks to their internal armor, as any hit in this location – even those rejected with no main armor damage – will result in localized flooding. Not ideal but considering that some of these tanks are liquid filled and the area is already designed to absorb damage (hence means for counter flooding) this was considered an acceptable design compromise. The deck armor is more complex but some rough calculations suggest that the deck armor is immune to penetration out to about 33,000yds or so.
To be honest, I don’t think that one can have a real good feel for how these ships are truly protected until FEA simulations become more available to where penetration events can be more precisely modeled on a complex target structure such as a ship’s hull. Then one can look at the effects of AP caps, windscreens, yaw etc. have on penetration. One should be able to determine, for instance, the BISMARCK’s deck resistance to various attack projectiles, or if in fact the STS strakes on the sides of the IOWA and SOUTH DAKOTA class can strip the AP cap of attack projectiles; things of that nature that are often debated with vigor.
Bill Jurens wrote:..... That is (probably) one reason that the Iowa Class retained homogeneous turret face plates even after the U.S. had perfected the technology to make Class "A" armor in the very heaviest thicknesses.
Bill Jurens
Another factor may have been weldability. Class B allowed retention of an all welded turret structure.
Being picky, but "At 16000 yards (not meters) with a new liner the 38cm just fails to penetrate, with the limit velocity being 1897 fps, and the shell hitting at 1889 fps" by no stretch of the imagination indicates that penetration is "improbable", it implies that it's very probable indeed - nearly half the time, in fact.
mike1880 wrote:Being picky, but "At 16000 yards (not meters) with a new liner the 38cm just fails to penetrate, with the limit velocity being 1897 fps, and the shell hitting at 1889 fps" by no stretch of the imagination indicates that penetration is "improbable", it implies that it's very probable indeed - nearly half the time, in fact.
Mike
Being picky,
1. I never said that penetration is "improbable", I said "...indicate penetration {much beyond these ranges} is unlikely...", particularly when using a used liner.
Sorry, I was thinking about the unreliability of the numbers rather than picking on an individual response, my apologies if that's the impression I gave.
My perspective was that the notional difference in velocities is well within the margin of error for calculated striking velocity, and well within the margin of variation in thickness for the plate, quite apart from any questions about lamination or the plain old random variations in results inherent in penetration results. So while the window of opportunity for the gun might be pretty slender, it certainly exists.
mike1880 wrote:Sorry, I was thinking about the unreliability of the numbers rather than picking on an individual response, my apologies if that's the impression I gave.
My perspective was that the notional difference in velocities is well within the margin of error for calculated striking velocity, and well within the margin of variation in thickness for the plate, quite apart from any questions about lamination or the plain old random variations in results inherent in penetration results. So while the window of opportunity for the gun might be pretty slender, it certainly exists.
Mike
And on the other hand, the "window of opportunity" for the 16"/50 to penetrate Bismarck's turrets is huge. Something like 30,000 yds on down.
