Bismarck against BB-57 South Dakota

[Byron Angel]

This particular data set for the 16"/45 with 2700lb projectile does not plot as a curve. It's rather hurky jerky and then suddenly at 30,000 yards the plot turns into a virtual straight line going steeply up. Can't be right. No way. I don't want to put the public spot light on the compilers of the table though.

I can see the deck penetration coming out virtually the same for the 16"/45 with 2240lb projectile and 16"/50 with 2700lb projectile. The lighter projectile will have slightly less velocity by then but it will have a slightly steeper angle of fall at long ranges as the result of that.

..... Dave,

I plotted the USN Vpen, Hpen and the striking velocity computed by my external ballistics s/ware. They all display as smooth curves for me. The steep increase in the slope of the Hpen curve starting at about 30,000 yards corresponds to the increase in striking velocity due to gravity effect upon the falling projectile simultaneously with accelerated increas in angle of fall, so I'm not seeing anything unusual there. Exactly what data set is plotting badly for you?

One thing I did note is that the 16/45 ballistic data in Campbell are given in uneven increments - i.e.: 10,000, then 16,000 then 20,000, then 26,000 yards, etc. - making alternating increments of 6,000, 4,000, 6,000, etc. Might that be the culprit?

Byron

p.s. - You analysis of the Hpen of the 16/45 2240 lb projectile versus that of the 16/50 2700 lb projectile corresponds to the USN data given by Friedman - their plots are very close from 28,000 yards out.

[Dave Saxton]

They all display as smooth curves for me.

That's how they should plot, and when they don't it's a major red flag that something is amiss.

The steep increase in the slope of the Hpen curve starting at about 30,000 yards corresponds to the increase in striking velocity due to gravity effect upon the falling projectile simultaneously with accelerated increas in angle of fall, so I'm not seeing anything unusual there

This is unusually steep and its no longer a curve. It is unusual in this case. It's a radical exageration of the deck penetration performance. Other plots would exhibit they same thing once they get to range where they will also attain similar angles of fall.

[Byron Angel]

They all display as smooth curves for me.

That's how they should plot, and when they don't it's a major red flag that something is amiss.

The steep increase in the slope of the Hpen curve starting at about 30,000 yards corresponds to the increase in striking velocity due to gravity effect upon the falling projectile simultaneously with accelerated increas in angle of fall, so I'm not seeing anything unusual there

This is unusually steep and its no longer a curve. It is unusual in this case. It's a radical exageration of the deck penetration performance. Other plots would exhibit they same thing once they get to range where they will also attain similar angles of fall.

..... Again, exactly what data set are you having this issue with?


Byron

[Bgile]

Doesn't Nathan's forumula have a break point at a certain angle of fall because he discovered it wasn't adequately describing the actual penetration which occurred at those angles? If so, it obviously wouldn't be a smooth curve and probably the end if the "normal" curve isn't steep enough so there is a break point.

[Dave Saxton]

Again, I don't want to put the spotlight on the complilers of the tables.

A break point at 30,000 yards for this gun should not be a proper methodology:

viewtopic.php?f=36&t=3163&start=0

Actually at these striking obliqities the real life performance is less than the predicted performance. Of course an angle of fall of 35* is still 55* from the normal.

[alecsandros]

p.s. - You analysis of the Hpen of the 16/45 2240 lb projectile versus that of the 16/50 2700 lb projectile corresponds to the USN data given by Friedman - their plots are very close from 28,000 yards out.

But the 16/45 2240lbs has a much shorter range than the 16/50 2700. So, at ~ 30km, the first gun/shell would be close to maximum range. So, the shell will naturaly fall at a steep angle.

The correct comparison would be with a 16/50 2700 at 45k yards, I think...

[lwd]

Looking at:
http://www.navweaps.com/Weapons/WNUS_16-45_mk5.htm
The max range of the 2240lb shell fired from a Mk5 or 8 wasn't that much less than that of the 2700lb shell fired from a Mk7. What limited the range of the 2240 was the elevation limits of the Colorado's turrets.

[lwd]

In one of these threads some questions were raised as to the ability of the SoDak's projectiles to reach Bismarck's "vitals" at longer ranges. Let's take a look. I'm basing this on the following references
First of all the armor diagram at:
http://www.kbismarck.com/proteccioni.html
And the penetration tables at:
http://www.navweaps.com/index_nathan/Pe ... States.htm
Let's focus on the range from 28,000 yards to 36,000 yards. From the table above the angle of decent varies from ~31 degrees at 28,000 yards to 45 degrees at 36,000 yards.
From the bottom up. A hit below the belt is possible. However it's not clear if or where such a shell would explode. Water tends to increase the angle of travel of the shell. However there is little to stop shells in this area. The Turbine rooms are reachable if the shell angle isn't increased too much and if the hit is relativly high on the hull. The magazines do not appear to be reachable unless the shell detonates under them. The shell exiting out the bottom of the hull is a distinct possiblity here.
Now for the belt. Effective penetration appears possible at 28,000 yards and partial penetration out to 32,000 yards. However none of would be expected to penetrate the scarp. It's worth noteing that that at 28,000 yards a hit above the 320mm belt but on the 145mm belt will miss the scarp and hit the 95mm deck after passing through another 30-45m of verticle armor. I'm not sure in this regime penetration can be conclusivly determined either way. It does look possible however. Above the upper belt there are shot lines that pass through the 50mm deck, 30mm of verticle armor, and the 95 mm deck. The penetration of the 2700lb shell in this regime varies from 173mm to 455. It does look possible that this armor array would stop the shell coming in from 28,000 yards. By 32,000 yards however the deck penetration is up to 274mm. This requires the "spaced array" to be over 50% more efficient than a single piece of armor. That seems to be asking a lot to me and the case gets worse as the range increases. The case is even worse over the turbine rooms where we are looking at 50/30/80 or 50/80 mm of armor.
We can also look at the turrets. The lower face is proof against effective penetration at these ranges but partial pentration is possible at 28,000 yards. Likewise the upper barbett while a little thinner is probably safe due to it's curveture. The same cannot be said for the upper face or tops of the turrets. The lower barbetts may also be at risk.
If we look at the decent angle for 28,000 yards i.e. ~31 degrees and the ship near the turret it looks like about 25% of the hits would fall under the belt, 25% on the main belt, 10% on the upper belt, and 40% on the deck up to the point where any penetration would be above the far scarp. The percentage of underwater hits is undoutbely high.
More later.

[Dave Saxton]

..Above the upper belt there are shot lines that pass through the 50mm deck, 30mm of verticle armor, and the 95 mm deck. The penetration of the 2700lb shell in this regime varies from 173mm to 455. It does look possible that this armor array would stop the shell coming in from 28,000 yards. .....

So based on your estimate the upper IZ limit is all the way out to ~28,000 yards. Thats pretty good! That would be about the same as Iowa or SD, or KGV against this shell would it not? 27,000 yards is the boundry to extreme range by USN doctrine.

Beyond 28,000 yards its no worse off than most any other battleship, but this is where the effects of de-capping and so forth still have effect and give the Bismarck a special advantage not enjoyed by most other battleships in minimizing the effects of hits. It's most unlikely that intact penetration in a fit state to burst by a de-capped and yawed projectile of the main armour can be achieved.

Another thing is the estimated penetration at a given range is based on a single plate. What is the total penetration when the effect of the blunt nose shape is taken out of the equation by yaw? What about the loss of mass due to removal of the cap?

I don't think your taking into account the compound obliquity involved with hits on the curved and angled lower turret face of 360mm KC. This compound obliquity means that it will likely reject battleship caliber rounds with striking velocities of less than ~ 505 M/s and angles of fall exceeding ~16*. At what range does the round still exceed a V of 505 M/s and have an AoF of less than 16*? The upper crown is laid-back 65* from the normal. This creates a very unfavorable striking angle for short and moderate range incoming rounds directly from the front. At longer ranges its becomes a matter of probability that this section will get hit from directly ahead.

[Byron Angel]

..Above the upper belt there are shot lines that pass through the 50mm deck, 30mm of verticle armor, and the 95 mm deck. The penetration of the 2700lb shell in this regime varies from 173mm to 455. It does look possible that this armor array would stop the shell coming in from 28,000 yards. .....

So based on your estimate the upper IZ limit is all the way out to ~28,000 yards. Thats pretty good! That would be about the same as Iowa or SD, or KGV against this shell would it not? 27,000 yards is the boundry to extreme range by USN doctrine.

Beyond 28,000 yards its no worse off than most any other battleship, but this is where the effects of de-capping and so forth still have effect and give the Bismarck a special advantage not enjoyed by most other battleships in minimizing the effects of hits. It's most unlikely that intact penetration in a fit state to burst by a de-capped and yawed projectile of the main armour can be achieved.

Another thing is the estimated penetration at a given range is based on a single plate. What is the total penetration when the effect of the blunt nose shape is taken out of the equation by yaw? What about the loss of mass due to removal of the cap?

I don't think your taking into account the compound obliquity involved with hits on the curved and angled lower turret face of 360mm KC. This compound obliquity means that it will likely reject battleship caliber rounds with striking velocities of less than ~ 505 M/s and angles of fall exceeding ~16*. At what range does the round still exceed a V of 505 M/s and have an AoF of less than 16*? The upper crown is laid-back 65* from the normal. This creates a very unfavorable striking angle for short and moderate range incoming rounds directly from the front. At longer ranges its becomes a matter of probability that this section will get hit from directly ahead.

..... You pose as many questions as answers here, Dave. Can you refer me to any reliable data on the degree of yaw induced by various thicknesses of armor upon various calibers/weights of projectile, and the effect such degrees of created yaw might exert upon armor penetration capabilities?

Also it is worth noting that that turret crown plate laid back at 65deg also improves the striking angle of falling shot considerably; a projectile with an angle of fall of 20deg will have a practical striking angle of 45deg.

Byron

[Dave Saxton]

There is no nifty rule of thumb that would predict that X amount of yaw will be produced if the yaw plate is Y calibers thick or something. Although if the yaw plate is also heavy enough to de-capp it would certainly have significant effect on the amount yaw eventually produced through the resultant shift of the center of gravity on the rate of precession.

The amount of yaw produced is the result of a very complex interplay of many variables, so it is rather dynamic. But to simplify, the main factor on the amount of yaw produced is not the thickness of the yaw plate, but the distance between the yaw plate and the main armoured deck. The amount of yaw will result on the interaction of the procession with the nutation and the time/distance between the plates and the rate of precession. The greater distances between the yaw plate and the main armour will almost always allow greater amounts of yaw to become manifest.

According the USN letter to Carnegie Steel in 1941, which alludes to the upper deck on the new USN battleships as a purpose designed yaw plate, there is a break over point where a minimal amount of yaw will cause the shell to strike the main armour, in the words he used, as "flat". The amount of armour that the shell must defeat is much, much, greater and the corresponding amount of energy required is also much, much, greater than a more optimal nose on impact.

I do have some modern US National Lab data on yawed oblique impact of projectiles into spaced armour. I don't have it right handy so I would be running the risk of misquoting the exact data. Nonetheless, I seem to recall that the amount of energy required to penetrate a given thickness of armour while yawed was very significant compared to that required to penetrate unyawed in the case of this array and projectiles. IIRC, if the yaw was nose up at impact, it was as if there was an additional 11* of obliquity, and if it was nose down on impact, an additional 9* obliquity at impact, in this case of this array and projectile. Note that any yaw whether negative or positive is always detrimental to penetration.

Yes, the angle-back upper crown becomes less ideal as the range increases, assuming it is struck directly from the front. This would be a case of biasing the design for maximum effectiveness at the ranges where it is more likely to be hit at the expense of its effectiveness at the ranges that it is less likely to be hit.

[Byron Angel]

There is no nifty rule of thumb that would predict that X amount of yaw will be produced if the yaw plate is Y calibers thick or something. Although if the yaw plate is also heavy enough to de-capp it would certainly have significant effect on the amount yaw eventually produced through the resultant shift of the center of gravity on the rate of precession.

The amount of yaw produced is the result of a very complex interplay of many variables, so it is rather dynamic. But to simplify, the main factor on the amount of yaw produced is not the thickness of the yaw plate, but the distance between the yaw plate and the main armoured deck. The amount of yaw will result on the interaction of the procession with the nutation and the time/distance between the plates and the rate of precession. The greater distances between the yaw plate and the main armour will almost always allow greater amounts of yaw to become manifest.

According the USN letter to Carnegie Steel in 1941, which alludes to the upper deck on the new USN battleships as a purpose designed yaw plate, there is a break over point where a minimal amount of yaw will cause the shell to strike the main armour, in the words he used, as "flat". The amount of armour that the shell must defeat is much, much, greater and the corresponding amount of energy required is also much, much, greater than a more optimal nose on impact.

I do have some modern US National Lab data on yawed oblique impact of projectiles into spaced armour. I don't have it right handy so I would be running the risk of misquoting the exact data. Nonetheless, I seem to recall that the amount of energy required to penetrate a given thickness of armour while yawed was very significant compared to that required to penetrate unyawed in the case of this array and projectiles. IIRC, if the yaw was nose up at impact, it was as if there was an additional 11* of obliquity, and if it was nose down on impact, an additional 9* obliquity at impact, in this case of this array and projectile. Note that any yaw whether negative or positive is always detrimental to penetration.

Hi Dave,

I by no means doubt that the interaction of a projectile with an armor plate can produce yaw relative to its line of flight. The essential question in my mind is to what degree. What amount of yaw, for example, might a 2in deck cause on a 2000+ lb projectile passing through it at 1500 or 1600 ft/sec - 10deg? 1deg? 0.10deg? i cannot even obtain a sense of magnitude.


Byron

[Dave Saxton]

In most data I have seen it has always been several degrees and many cases more than 10. It has never been a fraction a degree.

[Djoser]

All this talk of the devastating impact of a ton and a half of refined metal and explosive on the Bismarck's decks reminds me of the onslaught of the 15" one ton shells on the German battlecruisers at Jutland. I suspect it would have been the same if the SD and the Bismarck met. Getting hit with 3000 pounds of metal is going to hurt, any way you want to try it. The Bismarck at 50,000 tons was perhaps better suited to ride it out long enough to cripple an opponent, than the 25,000 ton battlecruisers taking hits from one ton projectiles at Jutland. And dishing it back out.

[Byron Angel]

All this talk of the devastating impact of a ton and a half of refined metal and explosive on the Bismarck's decks reminds me of the onslaught of the 15" one ton shells on the German battlecruisers at Jutland. I suspect it would have been the same if the SD and the Bismarck met. Getting hit with 3000 pounds of metal is going to hurt, any way you want to try it. The Bismarck at 50,000 tons was perhaps better suited to ride it out long enough to cripple an opponent, than the 25,000 ton battlecruisers taking hits from one ton projectiles at Jutland. And dishing it back out.

..... Twenty five years of technical progress needs to be taken into account. The 15in AP projectiles which hit the German BC's at Jutland in 1916 were imperfect designs which would break up upon striking face-hardened armor 6in or greater in thickness at average obliquities. By 1940 the strength and penetrating performance of AP projectiles (especially at higher obliquities) had very dramatically improved.

Byron