Bismarck vs. Iowa

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RobertsonN
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Re: Bismarck vs. Iowa

Post by RobertsonN » Mon Apr 11, 2011 4:10 pm

Nav Weapons gives original MV of 15 in guns as a high 2723 fps. When this caused problems, MV was reduced in the early part of the war to 2575 fps, still very respectable for the weight of shell.
Nav Weapons gives AA rof of 6 in guns as only 5 rpm. This was of use only in the long range barrage role, and it is not clear if they were ever actually used as such. The VVs did use their 6 in and 15 in for (probably ineffective) barrage fire.
The 18 in torpedo that exploded under Richelieu's stern certainly did not have a warhead as high as 1500 lb. As with Dunkerque, one hit caused multiple system failures (armament, fire control, turbines, electric plant, progressive flooding). Are you confusing the torpedo hit on Richelieu with the one on Dunkerque, which did cause depth charges to detonate as well for a much bigger explosion? The shallow depth was probably a factor as with the Italian battleships at Taranto and the Queen Elizabeth and Valiant at Alexandria.
Photographs of damage by shells and bombs to Jean Bart in 1942 show disintegration of the hull structure. If Bismarck had shown similar resistance to major ordnance it would have probably sunk after 20 to 25 minutes through structural failure on 27 May.

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Re: Bismarck vs. Iowa

Post by Tiornu » Mon Apr 11, 2011 8:20 pm

I don't know what it is about the French, but they seemed to have some pretty bad luck with depth charges. The night prior to the torpedo attack, a British team took a boat into the harbor and dropped a set of four depth charges near Richelieu's stern. The attack was deemed a failure as the charges failed to go off. However, they may have exploded sympathetically with the torpedo. The explosion reportedly lifted the ship's stern out of the water. The widespread, severe damage that Richelieu sustained was caused by either 388 lbs of explosive or 1548 lbs of explosive.
The switch to smaller propellant charges followed the inquiry into Richelieu's shell failure at Dakar. This was to ensure they didn't experience another failure of the base plate through the gas cavities. The shells used by Richelieu after her American refit didn't have the cavities; I don't know if they returned to the original MV, but the only reason not to would have been to reduce wear on the irreplaceable barrels.
Yes, the 6in guns were equipped with a barrage system.
You're certainly right that Richelieu was more susceptible to HE ordnance damage than Bismarck. However, I'm not sure what direct comparison we can make here. To carry as much explosive as a 1000-lb bomb, Rodney's and KGV's shells would have to weigh 21,000 lbs.

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Re: Bismarck vs. Iowa

Post by RobertsonN » Tue Apr 12, 2011 8:06 am

Dulin and Garzke give the torpedo warhead as 450 lb and, as you say, mention the possibility of depth charges as well. The full facts will probably never be known.
American and German battleships had bomb decks, which, amongst other things, reduced the size of holes that large instantaneously fuzed HE bombs could blow in this, the strength deck (Whitney in German Capital Ships of WWII gives this as the reason for the selection of 50 mm as the UD thickness in Scharnhorst). Another benefit is that large thin walled bombs with fuze delays would suffer casing damage on penetrating the bomb deck, which would reduce the force of the resulting blast. Some of the 500 lb SAP bombs that penetrated Tirpitz's upper deck detonated only very low order. RN battleships did not have a bomb deck but the armor deck was very high, sufficient to serve as an auxiliary strength deck up to sea state 5 or 6 in the event that the upper deck was torn apart in an action. And above this sea state, it was thought the enemy would not be able to score enough hits to impair the strength of the UD (Brown in From Nelson to Vanguard).
The machinery in the French ships was compact, light and relatively efficient (Dulin and Garzke). To shoehorn 150000/180000 shp into a space no more than 170 ft long by 62 ft wide at a weight of under 2400 tons was better than any contemporary. However, there were only two boiler rooms and two turbine rooms, so one hit might put half of the plant out of action. Likewise the electric plant doubtless realized weight savings by partly using 460 V. However, each of the three power plants produced only 230 V and so at least two plants were needed to operate some of the equipment. Most contemporaries had four plants which could individually work equipment at about half the French voltage. The problems with lack of power after local damage probably derives from this design choice.
The AA was very weak. The 100 mm gun had a modest rof of 10 rpm (NavWeapons) and its ceiling of 10000 m was marginal against high level bombers in the European theatre by 1941. Eight 37 mm were too few and the 13 mm ineffective.
With the value of hindsight, they might have shown better resistance to damage with a narrower SPS (23 ft width was more than any contemporary other than the VV) to allow for greater compartmention of machinery spaces. Whether the splinter deck was a good use of weight (as opposed to thickening the belt and main deck) is also debatable. It might have been possible also to transfer some of the weight for secondary armament protection to slightly thicken the UD, which was variable at about 25 mm.

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Re: Bismarck vs. Iowa

Post by Herr Nilsson » Tue Apr 12, 2011 11:51 am

Well, I own an original report of a German officer, who visited Richelieu to examine the ship and the damages. IIRC the French didn’t know anything about depth charges. They just mentioned a boat with negotiators investigating the ships anchorage. The damage was considered to be moderate according to the circumstances. Therefore it is speculated that the torpedo didn’t hit the ship but the shallow floor.
Regards

Marc

"Thank God we blow up and sink more easily." (unknown officer from HMS Norfolk)

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Re: Bismarck vs. Iowa

Post by RobertsonN » Wed Apr 13, 2011 8:57 am

Thanks for info; original documentation is the gold standard of our hobby.
There is a piece on the Marinearchive site about damage to Jean Bart. It appears there were two 1000 lb bomb hits close to each other aft with a third between the ship and the quay. There was one hit forward, probably 2000 lb. It is speculated that damage was unusually great because there was reflection of the blast off the quay. However, Jean Bart was not alone in having little protection forward (there was a 40 mm lower deck). Iowa had no more protection here (in fact less) and would appear to have been similarly vulnerable. In Bismarck the 50 mm upper deck extended beyond the citadel at both ends, presumably to give some protection against HE bombs. Apart from that there was a 60 mm waterline splinter belt and the entire hull above this forward and aft was 35 mm Wh. This was used as one of the lessons learned from the loss of the Lutzow at Jutland.
It would appear that it was sensible in attacking battleships to tailor bombs to individual ships. It is noticeable that only SAP and AP were dropped on Tirpitz. But for ships like Iowa and Richelieu, HE bombs would probably have been more effective in disabling them.

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Re: Bismarck vs. Iowa

Post by Bgile » Thu Apr 14, 2011 2:47 pm

To my knowledge the largest bomb carried on US carriers was 1600 lb APC.

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Re: Bismarck vs. Iowa

Post by RobertsonN » Thu Apr 21, 2011 1:27 pm

I see from the NavWeapons site, which I occasionally look at, that there has been an intensive debate about the supposed weakness of the Iowa near the top of the Class B belt. My position has shifted a bit on this one. Earlier, I was in the camp that there was a quite big weakness here.
However, you need to evaluate the computer program used as well as the ship. The M79 program for homogeneous armor gives accurate values for uncapped solid shot with very pointed shells (1.67 ogive radius) by WWII standards (mostly derived from tests with 3 in solid shot). And it gives the NBL (a limiting, or "grenz" in German, shot) not the EBL. Together, this is called in the jargon the "ideal NBL" case. The real case has APC with cavities for charges. How one gets from M79 to the real case is a very difficult and perhaps insoluble problem.
The joint between the Class A and B belts was undoubtedly above the 3rd deck. This allowed the lower belt to flex between the double bottom and the 3rd deck in the event of a torpedo or mine hit. This made the bottom of the 10.5 ft deep Class A belt only a few feet below the normal (55000 tons or so) waterline. And so the top of the class B belt could be hit by shells in the 15+ deg angle of fall range. That was probably a relative weakness but not, I believe, by nearly as much as implied by M79.
In the late War period the Iowa operated at up to 59331 tons. This put the Class B belt a few feet further down and removed this particular weakness. However, because of the narrow inclined main belt, the armored freeboard would then have been only a few feet and the Iowa was then a real internal inclined belt raft body design (more so than the Richelieu, which more armored freeboard and the MAD extending out to the ship's side).

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Re: Bismarck vs. Iowa

Post by RobertsonN » Thu May 12, 2011 8:08 am

Sorry, I meant to put this item in Richelieu v KGV, although it is relevant to the protection of all battleships. Perhps the moderator could move it?


Last week I got a copy of the book by Jordan and Dumas about French battleships. It is quite good.
On Richelieu it gives details of the armored decks. These had no armor backing. The type of joint used was the so called scarph, an angled joint. In the middle of a plate the thickness of 150 or 170 mm was better than 135 + 15 mm or 155 + 15 mm, which would have been the case if the practice used in Dunkerque had been followed. However, at the joint the thickness was of the form x + y where x + y = 150 or 170 mm and the effective thickness would have been less, perhaps much less. So these were weak points. Of course, all joints are weak points.
Others used thin backing plates, except the Germans who used welding. Welds are also likely to be weak points because of their different crystalline structure and material properties from the main plate.
The Richelieu was hit by one 15 in shell (out of 160) fired by Barham and Resolution at Dakar in July 1940. This struck the MAD, the result being a deflection with the MAD set down about 8 in. There was no damage below the MAD. Was such a set-down usual in such circumstances for other structural arrangements?
Does any one know if any tests were done on joints or whether they were simply accepted as intrinsic weak points that nothing could be done against, except have larger armor plates with fewer joints?

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Re: Bismarck vs. Iowa

Post by alecsandros » Thu May 12, 2011 10:46 am

Hello,
I am not sure I understand you properly:
- By "joints" do you mean plates put in contact with each other ? As in laminate plates ?
- The 15 inch hit on Barham was an explosive hit ? I.e. did the shell detonate above the MAD or was the MAD deformed by the force of impact alone ?

From my readings, the Italian, German and US navies had a good understanding of the limitations of using laminate plates (for instance 50+100mm put in contact or in very close proximity instead of using one single 150mm plate). The French, British and Japanese navies, as far as I know, had a less thorough understanding of this...
The formula used for calculating the effective thickness of laminate plates was sqrt (x^2 + y^2+...z^2)
For example, 1x50mm plate + 1x100mm plate in direct contact with each other would have an effective thickness of sqrt( 50x50 + 100x100 ) = sqrt (12500) = 111,8 mm

This limitation mainly concerns battleship shells impacting the laminate layers, as other shells (203mm and lower calibers) didn't pose a real threat to the main protection systems of WW2 battleships.

Allthough the laminate was known to perform less good than a single-plate, the option was selected in the North Carolina design (multi-layered decks), for instance, because of the structural constraints which needed to be fulfilled when building the ship (strenghtening of various portions of the ship). And, of course, a laminate plate-sheet was much easier to construct, transport and replace, as it was thinner and thus lighter than a single-sheet plate.

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Re: Bismarck vs. Iowa

Post by RobertsonN » Thu May 12, 2011 12:17 pm

The deck plates in Richelieu were in contact with each other although they were not laminated in the normal sense. Over most of the deck area there is only one plate as in German ships but where plates join each other there is an area that is effectively laminated, with one plate over the other, with a slanting joint. As I have never seen such a joining of plates before I wondered how the strength and effective ballistic thickness compared with other types of joint.

Your questions about the hit on Richelieu are very relevant. There was much damage above the MAD, so the shell probably detonated. The question is then, as you say, whether the 8 in set-down of the MAD was due to the force of the impact or the explosion. I must reread exactly what the book says.

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Re: Bismarck vs. Iowa

Post by Constance » Fri May 13, 2011 4:07 am

Hi guys, I'm new here. I would like to state my opinions on this forum, and participate in this discussion. :wink:

IMHO, Bismarck was a great ship, it was a combination of speed, firepower, and armor protection. At any case, I would like to confer that Bismarck could hold its own in a dual against Iowa class warships. It certainly had FC that could rival the Iowa's; I agree that the Iowa's had the best FC systems during the conclusion of WWII, though.

Can anyone answer how reliable the Iowa's FC system was?

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Re: Bismarck vs. Iowa

Post by Byron Angel » Fri May 13, 2011 12:45 pm

Herr Nilsson wrote:Well, I own an original report of a German officer, who visited Richelieu to examine the ship and the damages. IIRC the French didn’t know anything about depth charges. They just mentioned a boat with negotiators investigating the ships anchorage. The damage was considered to be moderate according to the circumstances. Therefore it is speculated that the torpedo didn’t hit the ship but the shallow floor.
.....John Jordan's and Robert Dumas's fine book "French Battleships 1922-1956" cites from the official report of RICHELIEU's captain ( Marzin ) that she was well hit by a British aerial torpedo which struck aft well below the turn of the bilge between the two starboard prop shafts as they emerged from the hull. The initial damage was magnified by the fact that the ship was in quite shallow water ( < 5 meters ) when struck; the hull breach measured 9.3 x 8.5 meters. Flooding spread rapidly into the after part of the armored citadel due to several identified factors -

[1] cracks in nearby decks and bulkheads created either by the explosion outright or by failure of defective/poor weld seams.

[2] flooding through the starboard shaft alley(s), which pierced the aft transverse bulkhead of the armored citadel.

[3] progressive flooding through cable tunnels, which also pierced the aft transverse bulkhead of the citadel and in fact ran throughout the ship. This flooding component was found to be exceedingly difficult to control.


For what it's worth.

B

Constance
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Re: Bismarck vs. Iowa

Post by Constance » Sun May 15, 2011 9:01 am

I was debating with another person about Bismarck, and I would like to ask anyone who knows what they are talking about to try to out debate it, I do not know enough about Bismarck, to be honest.
Umm, no. All battleships of the time were designed to defeat their own main guns. That is, a ship with 8x15in/52s has armor to protect it against the direct, and plunging fire of it's weapons. The ship has immune zones that were ranges where it's own guns, or lower, could not penetrate its citadel at all. Any ship with better armor would fair better. The Bismark took around 80 16in/45s, of which only a few would penetrate. They did knockout Bismarks turretts though cont.

Those same shells my not have taken out the turretts of Iowa or Yamato, as these ships had greater barbett armor. As for damage, Yamato was struck by 7 22.4in, 2,000lb warhead torpedos, before a final volley of 4 more, an HOUR later, sent her to the bottom 20 minutes after. Sorry, Bismark as a ship, had a wonderfully colorful history, as a design, 1930s mediocre.

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Re: Bismarck vs. Iowa

Post by Bgile » Mon May 16, 2011 8:41 am

If you read this thread, that's a continously debated subject and there is no easy answer.

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Re: Bismarck vs. Iowa

Post by lwd » Mon May 16, 2011 3:41 pm

Constance wrote:... Can anyone answer how reliable the Iowa's FC system was?
The weakest component of both ships FC system for long range engagments would have been their radar.
The Iowa had several redutant FC radar systems I believe. I'm not sure about Bismarck. I believe both ships had suffered some radar outages due to own ship gunfire. This and battle damage would tend to point to greater reduncancy being very important reliability wise. I don't have any details on just how reliable either radar was. By late war I would also expect US crews to have a lot more experiance with the systems though and this also has some implications for both reliability and operability.

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