Bismarck vs. Iowa

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alecsandros
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Re: Bismarck vs. Iowa

Post by alecsandros »

Thorsten: getting back to the 8,8 cm shell perforating 140mm homogenous plate at 45* obliquity. From your experience, what do you think would have happened if the plate would have been face-hardened, in the manner of KC n/A (35-40% cimentite layer, 650-700 Brinell at face surface, etc) ? Would a perforation in fit condition to burst still be probable ?

Thanks,
Alex
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Re: Bismarck vs. Iowa

Post by delcyros »

J. Sitz goes into some details in this question in his article for the Lilienthal-papers (p.109-113).

The PzGr.39 had the aility to penetrate almost any thickness RHA armour in a condition fit to burst, provided that the velocity was high enough and shatter didn´t set in.
In one case, he cites a trial with 7.5cm standart APC impacting a 200mm RHA plate (2.67 cal thik for the 75mm APC) with a striking veloity of in between 1020 and 1090 m/s @ 60 deg (=30 deg US definition).
In all three cases the projectile stayed intact with not even nose damage suffered. One of the three depleted all energy and remained embedded in the plate (german "Grenz" definition) where projectile damage is largest but the projectile stayed intact. In this case it´s still intact but only "Grenz"-definition is used because the projectile didn´t penetrated completely even though it remained in an intact condition fit to burst (="heil"). That´s also why You see the definition "Grenz-" and "Heilbelibkurven" fall together in the GKdos-100 curves for penetration of homogenious armour.

Sitz further expands upon the question of KC -performances:

"in trials with cementated plates of 100 to 140mm thickness at 30 deg (=60 deg in US definition) we haven´t been succeeded in getting the mass produced APC penetrating in intact condition fit to burst."

He displays a 100mm trial plate to be attacked by 75mm PzGr.39 at 30 deg with a striking velocity of 740 m/s but out of 18 impacts only one stayed intact without any damage visible and another penetrated with only nose damage but the majority broke up, exposing the cavity.
he notes that:

"The projectiles for high (penetrative..)performance are to be manufactured with an armour piercing cap in mass production, even while we may succeed that isolated, very good charges of projectiles may achieve higher penetration without a cap"

This is a reference to the differences in hardening treatment of these projectiles. Normal Krupp naval L4.4 APC received the sheath hardening treatment, which gradually lowered the hardening from the outer surfaces to the inner cavity across the projectile with very hard side walls but a soft cavity.
This treatment was more expansive and time consuming than the decremental hardening treatment used for standart Krupp army APC, such as the 7.8cm PzGr.39 (one straight line -the nose hardest, mid body temepered and base soft).

With a navy-like sheath hardening treatment the 7.5m and 8.8m APC may not require armour piercing caps to stay intact at very high striking velocities.

The later lots of Krupp L4.4. 40.6cm APC by the Bochumer Verein (not from the same family as the 20.3cm, 28.3cm & 38cm L4.4 APC, owing to a different W(d^3) fator while otherwise pretty similar in hardening treatment) could defeat in trials 385mm KC/n.A. (0.95 cal) at 30 deg with 500m/s striking velocity in a condition fit to burst (nose damage but cavity remained closed and intact). However, the same shell from other manufacturers had problems to achieve this and the reason for this may have been less careful controll of the hardening slope in the projectile.
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Re: Bismarck vs. Iowa

Post by Byron Angel »

Just a brief thank you to Thorsten and Delcyros for sharing some terrific German material that might otherwise never have become available to us English speaking monolinguists.

B
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Karl Heidenreich
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Re: Bismarck vs. Iowa

Post by Karl Heidenreich »

The importance of this discussion and the information that we are obtaining of it is beyond any value. Things are getting more than clear now.
An appeaser is one who feeds a crocodile, hoping it will eat him last.
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RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Reflected a bit while away at the weekend on Bismarck v Iowa. It seems that the 2700 lb shell with its great penetration was designed with Japanese ships in mind. Against Bismarck it had the advantage of good down range deck penetration but was unlikely to penetrate the side + sloped deck combination. For penetration, the 16/45 would seem to be better against the Bismarck than the 16/50 because it had better deck penetration and the superior vertical penetration of the 16/50 did not come into play much; Both could penetrate turrets and barbettes but neither the side + slope armor. Ballistically the German gun was superior to the 16/45 (danger space, time of flight) but the 16/50 was probably about the same down range (unfortunately the figures in NavWeapons are for different ranges so a comparison is difficult).
The German gun probably had a small advantage in rof, enough to make up for one gun less (2.125 v 2 needed for equality), and if it penetrated would do about the same amount of damage as the much heavier American shell because both had closely similar charges. Blast effects are entirely dependent on charge and the Germans considered that splinter effects were too: splinters from a 15 in APC could penetrate 30 mm Wh while those for a nose fused HE could penetrate 40 mm Wh, with a base fuzed HE in-between.
So the 2700 lb shell did not gain much in destructive effect on penetration compared with the lighter guns of European battleships. This was probably a trade-off. The first priority was to penetrate what was expected to be very thick Japanese armor. The Japanese 18 in shell had little advantage in penetration compared with the US 16/50 but had a much larger charge (about 70 lb to 40 lb) and so would do more damage if it did penetrate.
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Re: Bismarck vs. Iowa

Post by alecsandros »

Hello Robertson,
These are almost precisely the same thoughts I came about.

As an addition, in a showdown between BS and Iowa, the essential components would be vulnerable as follows:

Bismarck resisting Iowa fire

- radars (3), directors (1 primary, 1 secondary, 4 tertiary - one for each main turret) and other sensors - vulnerable at any conceivable range; their armor was to thin to stop 40.6 or 12.7cm gunfire.
- BS con towers/comm shafts (1 primary, 1 secondary of each)-> vulnerable at about 0-25km / 0 km [the secondary comm shaft would actualy be vulnerable at about 18-20km, but the primary one should stay intact against any hit, because the shell would be de-caped by the upper-armor belt or the upper-armored deck, and the 220mm thick rounded armor of the comm shaft was more than enough to stop a de-caped (and probably yawed) shell]
- BS ploting rooms (2) -> vulnerable at over 27km from plunging fire; even a non-explosive hit would cause great damage to the ploting room.

- BS main turrets (4)- > vulnerable at about 0-27km
- main magazines (4) -> vulnerable at over 25km from plunging fire; even a non-explosive hit could trigger a catastrophic explosion.
- secondary magazines for 15cm guns (6) -> only partialy exposed to direct fire; vulnerable nevertheless to plunging fire at over 25km

- machinery -> possibly vulnerable between 15-20km to diving shells. vulnerable at over 23-25km to plunging fire.

Total protected waterline: ~ 70%

Iowa resisting Bismarck's fire

- radars (4), directors (4 ?) and other sensors - vulnerable at any conceivable range; same as above.
- Iowa's con towers/comm shafts (1 primary, 1 secondary of each)-> the primary vulnerable at 0-18km; secondary I don't know
- Iowa's ploting rooms (2) -> vulnerable at 0-24km against Bismarck's fire.

- Iowa's main turrets -> theoreticaly protected at any range greater than 10km. Practicaly, the energy of an impact at 10-15km would still be enough to incapacitate the turret even without perforation.
- main magazines (3) -> theoreticaly invulnerable to 38cm shells. The sloped belt armor (310mm@20*) and the additional armored bulkhead (100mm thick on the sides) made a full penetration very unlikely, even for very good quality shells.
- secondary magazines (10) -> vulnerable at 0-25km against 38cm shell fire.

- machinery - only a diving hit could potentialy endanger the machinery. Given the deep belt, I don't think it is likely.

Total protected waterline: ~ 51%

=========

So Bismarck's main vulnerability comes from plunging fire, with additional degrees of problems coming from the turret and the con tower's armor. Additionaly, a lucky underwater hit could take out part of the machinery, allthough exactly how much of it would be put out of action is hard to say, given the good internal compartimentaion and systemic redundancy.

Iowa's main weakness can be seen at its secondary magazines, which, when hit, would explode violently, taking out many lives, and onboard sensors. This would affect the ship's fighting capacity quite a bit. The lesser protected volume also increased chances of rapid flooding in the fw and aft parts of the ship, which could cause imbalances, lists, and loss of speed, altering the fighting capacity.

At ranges of < 20km, after obtaining a good firing solution, Bismarck could put 21-22 shells/minute in the air (3shells/minute x 90%), whereas Iowa could fire 16-17 actual shells (2 shells/minute x 90%). However, at ranges > 20km, the difference in rof would be negligible, giving the Iowa the advantage.

Bismarck's gunnery was calibrated to fire closely grouped salvos, while Iowa's was designed to "saturate" a given surface. Thus, a salvo from Iowa would be more likely to score a hit. However, if it would hit, Bismarck was more likely to score 2 hits/salvo.

Both ships guns were tri-axialy stabilized, and an automated system linked radars-ploting rooms-turrets, giving them the capacity to manouvre while firing. This was somewhat better for Iowa, as it also had auto-turret rotation, at up to 4*/sec.

=========

P.S.: Perforations coming from various ballistic tests; homogenous armor considered roughly equal in the given thicknesses; perforations at "theorectical impacts", with 0* additional obliquity to the angle of fall/armor slope.
RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Thanks for very complete description. In general I agree. Bismarck vulnerable over 25 km. Friedman gives the Iowa as vulnerable to the 16/50 at over 27400 yds (25500 yds to the 16/45 2240 lb). Iowa safe against Bismarck at long range. So Iowa might gain a possibly decisive advantage at over 25 km. But to do so it would need to score hits at a greater range than any at which one battleship ever hit another battleship or any other ship.
I would put the Iowa as vulnerable to the Bismarck inside about 21.6 km. What is the source for the extra 4 in bulkhead at the side of the Iowa's magazines? This is not mentioned in any of the sources I know.
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Re: Bismarck vs. Iowa

Post by alecsandros »

I'm at work now, so quoting from the top of my head :D

I don't know where I read about the Iowa class armored bulkeads, but that's the way I remember it: 200mm thick STS armor for the forward/aft parts of the bulkheads and 100mm thick STS to the sides. I remember a design note, possiblyfrom Friedman, where the extra 100mm armor was explained as necessary due to the newer APC shells, capable of destroying sloped-armor much better than expected when the South Dakota (onto which Iowa class was based) class was built.

Also, I could be wrong :)

Cheers,
ALex
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Re: Bismarck vs. Iowa

Post by lwd »

RobertsonN wrote:...So the 2700 lb shell did not gain much in destructive effect on penetration compared with the lighter guns of European battleships. This was probably a trade-off. The first priority was to penetrate what was expected to be very thick Japanese armor. ...
There are a couple of factors that you left out however. Post penetration the shell can do a number of things: 1) Detonate high order, 2) Detonate low order, 3) Remain intact without detonation, 4) Breakup without detonation. To fully evaluate the damage potential of different rounds the probabilities of these events and their resultant damage needs to be considered. I submit that in the abscence of a high order detonation the momentum and energy of the shell are important parts of the damage potential. It's also clear that it was not uncommon for battleship caliber shells not to detonate. Unfortunatly I don't have much to contribute as to the actual numbers involved here.
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Re: Bismarck vs. Iowa

Post by lwd »

The protected waterline numbers however are a bit misleading. Out to well over 30,000 yards Iowa is capable of penetrating the armor at the waterline of Bismarck and for the protected area there is a good chance for a proper high order detonation. On the other hand an AP round hitting Iowa in the unprotected waterline area will likely be a through and through. Which while it could allow for flooding depending on where the hit is will likely not result in a high order detonation. That's the whole idea behind AON armor.

I'm also not sure that a 15" hit on the turret will necessarily put it out of action. I would think that highly dependent on the angles involved.
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Thanks for balanced comments. This is not an AON site! I certainly acknowledge that KE was an important factor in the event of failure of the shell to detonate high order.
What I originally had in mind was that the US ships had armaments that enabled them to be significantly more effective against the Yamato than the Bismarck would have been. However, the emphasis on armor penetration against very thick armor did result in relatively small explosive charges.
The Bismarck's armament, as I see it, was more optimized for use against ships up to the 45000 ton category. Any fast battleship of such displacement was likely to have armor thickness restricted to a value against which the 15 in gun would be useful. The RN went for even larger charges (so even the 14 in shell had a larger charge than the 2700 lb US ones). And had the Lion class been eventually built SAP shells with bursters three times as large (150 lb) would have made a comeback. But that was the British approach, to disable a ship before sinking it, probably with torpedoes.
As for the Iowa's turrets Friedman says they were proof against its own guns down to 20000 yds, so against Bismarck I'd guess 22000 yds. Anything inside this, such as a jammed turret, would be impossible to predict.
A couple of points: while in some ways the Bismarck's low armored deck was a disadvantage, it did have a lower effective target area than the normal type, because any shell hitting the slope on the far side would be very unlikely to penetrate. Secondly, because the Iowa had its belt inboard, shells that did not penetrate would cause considerable structural damage with flooding, especially if they were deflected downwards, and this would be irrespective of target angle. Thirdly, Bismarck's belt probably gave it reasonable protection at long range when the target angle was less than say 60 deg, which would be typical of the tactics the Germans were likely to employ.
Last edited by RobertsonN on Wed Jun 15, 2011 4:12 pm, edited 1 time in total.
alecsandros
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Re: Bismarck vs. Iowa

Post by alecsandros »

lwd wrote:... Out to well over 30,000 yards Iowa is capable of penetrating the armor at the waterline of Bismarck and for the protected area there is a good chance for a proper high order detonation.
I don't think so. The normal fuze delay for 2700pdr was 0.033sec. The German ship had 2 or more armor layers facing the most likely trajectories , and a shell would be decaped and fuzed by the first layer, but it will hit the second layer before the fuze runs out, causing it to become a dud. This is what happened to the 1600pds bomb that perforated deep inside Tirpitz in 1944 during an air attack.
lwd wrote:I'm also not sure that a 15" hit on the turret will necessarily put it out of action. I would think that highly dependent on the angles involved.
At 15km, the impact energy of a 38cm shell would be around 130MJ, which is quite abit. Of course, it doesn't necessarily has to put the turret out of action, but there's a good possibility for it...
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Re: Bismarck vs. Iowa

Post by lwd »

alecsandros wrote:
lwd wrote:... Out to well over 30,000 yards Iowa is capable of penetrating the armor at the waterline of Bismarck and for the protected area there is a good chance for a proper high order detonation.
I don't think so. The normal fuze delay for 2700pdr was 0.033sec. The German ship had 2 or more armor layers facing the most likely trajectories , and a shell would be decaped and fuzed by the first layer, but it will hit the second layer before the fuze runs out, causing it to become a dud. This is what happened to the 1600pds bomb that perforated deep inside Tirpitz in 1944 during an air attack.
There's quite a bit of difference between a 1600lb bomb and a 2700lb AP round. For instance from http://www.wehrmacht-history.com/luftwa ... -bombs.htm
The German PC500 AP bomb weighed in at 539 kg (~1200lbs) and had a filler of 78kg(~170lbs) and the PC1000 weighed in at 1,042kg (~2300lbs) and had a filler of 152kg (335lbs) as compared to the US 2700lb AP shell with ~140lbs of filler. The implication is the AP round is considerably more robust.
lwd wrote:I'm also not sure that a 15" hit on the turret will necessarily put it out of action. I would think that highly dependent on the angles involved.
At 15km, the impact energy of a 38cm shell would be around 130MJ, which is quite abit. Of course, it doesn't necessarily has to put the turret out of action, but there's a good possibility for it...
It is certainly possible. If it hits the turret square on it's very likely but if it glances off a facet of the turret ... maybe not. Also shells impacting near the turret can potentially put the turret out of action or cause problems with it's operation. For instance look at the results of hit 26 here:
http://www.navweaps.com/index_lundgren/ ... alysis.htm
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Re: Bismarck vs. Iowa

Post by alecsandros »

lwd wrote:
There's quite a bit of difference between a 1600lb bomb and a 2700lb AP round. For instance from http://www.wehrmacht-history.com/luftwa ... -bombs.htm
That's not the point; the point is that a 0.033s fuze delay shell would be decaped by the first armored layer, and than shatter against the second. The fuze would not go off at all, because it was a mechanical fuze, and rapid changes in the direction of movement would make it ineffective. Even if it wouldn't shatter (which is difficult to asume, given the properties of whotan and KC n/A armor) the fuze would almost certainly be rendered blind, given to yaw effects and off-center perforation.
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Re: Bismarck vs. Iowa

Post by RobertsonN »

Did the US 1600 AP bomb have a cap?

Just to enlarge on a point I made yesterday; about 60 target angle. In fact the Battle Fighting instructions for Bismarck against Nelson (1940) gave the main fighting range as 12000 to 16000 m and the advisable target angle as at most 60 deg. The Germans credited the Nelson's 2048 lb with 2755 ft/s MV, so the vertical penetration might have been comparable with Iowa's guns. Using the pessimistic armor penetration formulas they used they thought this shell could penetrate belt + sloped deck out to 27200 m at 90 deg target angle, falling to 19400 m at 70 deg target angle and zero at 50 deg target angle. Hence the 60 deg recommendation. Deck penetration was from 23800 (machinery) and 29700 m (magazines). The unprotected side above the belt, the unprotected bow section and large superstructure of the Nelson were mentioned in the choice of shell. Clearly HE would be fired at some ranges. In fact because of the three types of shells carried, the German ships could not carry out a really long engagement using APC alone.

While the logic of the nothing part of AON is impeccable, the Denmarck Strait action showed some limitations to this concept of protection. Control functions on the POW were quite badly affected by two shells that passed through the bridge area. Neither exploded, but there was a good bit of splinter type damage from fragmentation of the windscreen and possibly material the shells passed through. Another hit struck a crane and resulted in an air burst which temporarily disabled another secondary director and the radar room. This hit was really in the fluke category. The hit through the Bismarck's bows was the one that caused the ship to head for France. Although the underwater hit was more damaging, it had little effect on the ship's fighting capacity, whereas the bow hit reduced the ship's range, which was decisive.
As a result of this experience the Vanguard had much more extensive splinter protection than the KGVs. Friedman says IIRC that US ships also had much splinter protection fitted to control positions, showing some dilution of the AON concept.
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