Bismarck vs. Iowa

[Dave Saxton]

I don't want to jump on a new member but just to correct a few things:

1. Better radar. The Bismarcks radar was non-operational after the initial fight with the Hood. This allowed the Sheffield to make visual contact at 7 miles, and again an hour and a half later at 6 miles. No radar also left the Bismarck wasting precious fuel after the Bristish had lost radar contact, where an Iowa's radar would have probably detected that the British ships were searching for it. The Iowa's radar was very good and had a range of about 24 miles.

This is not correct. One of Bismarck's forward radars was knocked out prior to the battle with the Hood, but the other two sets remained in operation and they remained in operation after the battle with the Hood. Moreover, the British found from interrogations of prisioners that the 1 faulty radar was probably repaired and returned to operations later the same day. Indeed this is likely correct as the Bismarck was equipped with 1940 model sets which could be repaired and recalibrated at sea. These sets had a typical battleship to battleship range of 30km or 33,000 yards.

It is a little unfair to compare a 1941 ship against a 1944 ship

Yes it is, but we can compare the Tirpitz's 1944 radar suite and its AA performances. Bismarck had it still been around in 1944 would have been about the same as Tirpitz. Tirpitz had three different types of active radar in early 1944. There was a FuMO62 Hohentwiel K general tactical radar. This radar had it's antenna mounted on the foremast. It had an illumination power of 100 kw. Its typical effective range was equal to the USN SGII sets but it was more accurate. Tirpitz was equipped three FuMO26 Seeart sets. These radars were for directing gun fire. These sets were extremely accurate and with a range extending to as high as 39km and they were fully capable of directing blind fire. Tirpitz was equipped with a FuMO213 Wuerzburg D AA radar. This radar was second only to the US Army's SCR584 as the best AA radar of WWII.

Better rudders, in a side by side arrangement, rather than one in front of the other.

Actually Bismarck's rudders were also side by side.

The problems that led to the Bismarck's sinking would likely not have plauged an Iowa Class.

Most if not all of the problems which plauged Bismarck could have happened to the Iowa as well. Certainly had Iowa had its rudders disabled by a torpedo it would have meant the same fate.

I agree that the Iowa's longer legs would be an advantage, but Bismarck did not leave Norway with its tanks toped off either.

[Bgile]

Rosspest,

Generally here you will find that the prevailing belief is anything you find on Tirpitz/Bismarck at the same chronological point in the war is believed to be equal or better than the same type of thing on an Iowa class battleship, or else it's something that doesn't matter. Note that even in acknowledging the greater range of Iowa, Dave qualified it by implying that Bismarck didn't top off her tanks at the last possible moment, and that if she had she would have been able to outrun the British even with her battle damage. So in practical terms her range was quite sufficient to do what the Germans wanted her to do, and so was not a point of inferiority.

[Dave Saxton]

Thank's for reading into my post things I did not write nor imply.

[Bgile]

Thank's for reading into my post things I did not write nor imply.

You're welcome, Dave. :)

I think you are very intelligent and I think that some of the things you say reflect beliefs that are seldom expressed directly. However, and of course this is only my opinion, if one takes the entire body of your posts here and elsewhere they demonstrate in their entirety a clear bias in favor of German equipment. I agree with some of your always excellent presentation and disagree with other parts, but your posts are always favorable to the Germans and I think my reference to the fuel situation is relevant. An Iowa class ship has better range, so you needed to find a way to make the difference in range insignificant to Bismarck's survival.

Another example is the US extended belt, which protects the citadel from underwater shell hits. I think that would have prevented machinery space flooding from the 14" hit below Bismarck's belt armor. You simply stated you didn't think the US scheme would work. Maybe you think you aren't biased, but it appears to me that you are.

[Dave Saxton]

All I did was set forth some facts.

[lwd]

Indeed some facts, some opinions, and some rather critical aspects not addressed.

[Thorsten Wahl]

Another example is the US extended belt, which protects the citadel from underwater shell hits. I think that would have prevented machinery space flooding from the 14" hit below Bismarck's belt armor. You simply stated you didn't think the US scheme would work. Maybe you think you aren't biased, but it appears to me that you are.

kombi.jpg (12.06 KiB) Viewed 1542 times

I made a short gfx for some impact trajectories
in blue Bis scheme
in black Iowa scheme

red lines trajectories of 10, 15 21 and 36 degres AOF, all these trajectories are likely to pass under Bis belt at around 2,3-2,5m (~50.000 ts displacement)

the green points are the explosion sites for impact speeds with 0,035 fuze delay set off at impact on water
I didnt consider deceleration due to water
but i consider impact speed on belt/torpedobulkhead with 1/2 of impactspeed on water
at the designated AOF the US and the german projectile differ mostly less then 10m/s in their impactspeeds

in reality the projectil should explode around at around 3/4 of the underwatertrjajectory i considered here.

surprisingly the us belt also didnt widthstands the 38 cm projectile

[Bgile]

Thorsen, how did you determine the correct trajectory with the shell yawing to a great degree, which usually happens with underwater trajectories? What did you assume happened to the AP cap? How did you determine penetration? I thought it would be pretty hard to compute considering the amount of yaw which typically happens in water.

My point was predicated on the British 14" shell going off in contact with the US lower belt extension. It would probably have prevented fragments from getting behind it and if it didn't, it would decelerate them so much that they wouldn't penetrate the US holding bulkhead. In the case of Bismarck, the British shell didn't encounter any armor until it arrived at the holding bulkhead, where it exploded.

[Thorsten Wahl]

I did not determine any change in trajectory as i have absolutely no information about this
no information about shape of trajectory
almost no information on deceleration
I read somwhere in british reports that they expect a remaining underwater trajectory for 15"(?) shells of about 120 feet.
and Bill Jurens states somwhere half of impactspeed after 45 feet underwatertravel if I remeber correctly.

if there is some deflection upwards this will increase the pentration abilities of the projectiless as the obliquity on impact on the plate will be something less
but the remaining lenght of trajectory until detonation should be the same.

And yes if the projectile detonates in front of the Belt/TDS both pieces will be able to catch fragments, but probably not all.

As there are no reports available from systematic research I choose the easiest model. If you have some better informations it should be useful to take this into account.

[RobertsonN]

Just to point out that there has been a discussion in the Vittorio Veneto section that has a bearing on the Iowa/Bismarck discussion.

If you look up

http://forum-marinearchiv.de

and then go to the discussion "Bismarck/Scharnhorst: why not inclined belts?''' (it is in German) and look at pp. 16 and 17 you will find calculations done for various battleships using Nathan Okun's program. The results are interesting. Sodak/Iowa come out of the comparison quite well. However, they do have a zone of vulnerability at the top of the lower (class B) belt at all ranges over about 14000 yards.

This site has excellent graphics and is well worth a look even if you can't read German.

[Bgile]

I did not determine any change in trajectory as i have absolutely no information about this
no information about shape of trajectory
almost no information on deceleration
I read somwhere in british reports that they expect a remaining underwater trajectory for 15"(?) shells of about 120 feet.
and Bill Jurens states somwhere half of impactspeed after 45 feet underwatertravel if I remeber correctly.

if there is some deflection upwards this will increase the pentration abilities of the projectiless as the obliquity on impact on the plate will be something less
but the remaining lenght of trajectory until detonation should be the same.

And yes if the projectile detonates in front of the Belt/TDS both pieces will be able to catch fragments, but probably not all.

As there are no reports available from systematic research I choose the easiest model. If you have some better informations it should be useful to take this into account.

You see a few tears in Bismark's holding bulkhead when a 14" projectile detonates next to it. But then, when the same shell detonates against a much thicker US bulkhead the splinters are supposed to do the same amount of damage and then pass though another TDS bulkhead and then a holding bulkhead about the same thickness as in Bismarck and you don't think the outcome won't be any different.

It is interesting to me how you choose a straight ballistics model with no comment about yaw in this case, where if you are describing an attempt to penetrate Bismarck's deck's you don't want to do that at all. You think the properties of yaw are going to flip the US 16" shell around and render it unable to do any damage to Bismarcks engineering spaces through the deck armor, but if the German shell travels through 50 feet of water and then encounters multiple layers of armor plate of the same total thickness, then that will of course be extremely effective.

The bias here is incredible, and I don't think it's worth posting here anymore. You guys begin with the assumption that Bismarck is superior to any possible opponent and then go on to find reasons why. It saddens me because I like to share information like this, but I just don't think I get a fair hearing here.

Then there are the political posts that make me want to throw up.

[Herr Nilsson]

You guys begin with the assumption that Bismarck is superior to any possible opponent and then go on to find reasons why.

I tend to disagree. It's not only that. There is often the assumption that Bismarck is inferior to any or at least most possible opponent. I personally don't like this inferior/superior threads. In most cases it's a matter of taste what is considered inferior or superior. Is Iowa a more powerfull weapon than Littorio, because of it's range? Does anybody think Iowa would have the same range in case of beeing designed to operate in the Mediterranean sea. I don't think so. IMHO there is no fair answer at all to the question, which ship is inferior or superior. I personally look up to all design engineers of any nation. American, British and Japanese design engineers were very smart. But also French and Italian. And German, too.

As long as books like Ballantyne's "Killing the Bismarck" are published, where the same old story about the unprotected communication and electrical lines is told again, we all are fighting a loosing battle anyway.

Then there are the political posts that make me want to throw up.

This time I tend to agree.

[Thorsten Wahl]

It is interesting to me how you choose a straight ballistics model with no comment about yaw in this case, where if you are describing

In the case of deck pentration there are statements regarding yaw in the Unterlagen zur Bestimmung der Hauptkampfentfernung.... in other german and also in british and US ballistics reports, so I am more secure that yaw affects projectiles after impacting one or more plates. There are also centrifugal laws. If I interprete these laws i tend to assumme that disturbances have greater impact on relatively longer cylinders, if we are taking into account the length-diameter ratio.

in the case of underwatertrajectories the available amount of useful information is somewhat insufficient as I said before.
Im not flat rate(pauschal-I hope this translation is correct) saying that a certain arrangement was better then another one because it has a feature the other dont have.
The underwater impact marks on the POW hull from the german shells were, as far as I know of circular shape.

Usually I combine the information I have and calculate and try to balance the outcome. Especially if ther is some uncertainty i try to get additional informations.

In about 4,5m -5m depth the US belt has a thickness of about 100 mm I would say from the available informations. The 38 cm projectile would perforate this plate at around 200m/s impact speed. This result was surprising to my as I said. But I think my conclusion is permitted.

[RobertsonN]

To me, it is obvious that the Iowa had better underwater protection than most other battleships apart from the larger Yamato.

However, it appeared to have a narrow zone of vulnerability just below the main belt. This is shown in those German and American calculations done on that marine-archive site using Nathan Okun's program. Okun (?) called this zone between 14000 and 28000 yds, the zone of 'mixed' results. Where were the 3rd deck and the bottom of the main belt in relation to the waterline? Friedman says the Iowas had a 6 ft deep double bottom (a superior feature) and that the machinery spaces were 26 ft deep, putting the 3rd deck at 32 ft above the outer bottom. The armor heights given by Friedman are consistent with this. He put the lower (class B) belt as of 28 ft width and the main (class A) belt at 10.5 ft (very generous areas). Angled at 19 deg gives effective vertical heights of about 26.5 and 9.95 ft, respectively. The joint between the belts (at about 3rd deck level) would be about 3 ft below the waterline (35 ft) at normal maximum displacement (about 55000 tons) and about 5 ft below the war overload (59331 tons) waterline (37 ft). The top edge of the main belt was about 3 to 4 ft inboard from the side (saving on deck armor weight and improving stability).

So unless the Iowa was near to the war overload displacement, a shell striking at about or just below the waterline at ranges over about 14000 yds would have been able to strike the top of the tapered upper belt (average 11.68 in class B) and, if the target angle was close to 90 deg, would likely penetrate. At 30000 yds the VV shell could still penetrate even assuming that the shell had been decapped by the 1.25 in thick hull skin.

Why was the main belt so narrow? North Carolina had 14.25 ft. This would have been enough to make the Iowa safe in this scenario. A deeper class A belt without any weight penalty would have been much preferable ballistically. Perhaps it was felt that putting the joint between the belts lower would have resulted in poorer protection against torpedos, or maybe the arrangment was chosen because the respective belts were better supported by the decks and triple bottom in the arrangement chosen.

The Bismarck was vulnerable to diving shells but it was not vulnerable to conventional hits occurring just below the waterline.

[lwd]

I seem to remember reading that one of the desing features of the Japanese "diving shells" was to keep their trajectory point first underwater. It's my understanding that most shells will end up traveling base first underwater if they do so for any distance. It has been proposed that the UW hit on POW by Bismarck is an example of this. Needless to say traveling base first will have considerable impact on both pentration and the probability of the shell detonating if the fuze was not initiated by impacting the water.