Bismarck vs. Iowa

[Thorsten Wahl]

There is also a problem with the homogeneous penetration calculations

Naab, wich is reputed to use Nathan Okuns calculations, predicts a better ballistic performance for Wotan weich compared to Wotan hart. This is wrong.

So the of accepted correlation of utilized values in the calculation could be something different from the reality.

[dunmunro]

I know the properties of D-steel and must disagree that it had good armour properties. Certainly not 90% of NCA. D Steel was typically 80ksi tensile at which point it was at ~17% elongation. At ~24% elongation NCA would have been at 117ksi tensile. It would be a stretch to assume it had 80% the ballistic resistance of NCA.

You might be correct (and I'm not being sarcastic), but the RN used it extensively for protective and splinter proof plating, so it seems that the RN and Okun disagree with you.

[Bgile]

I've never seen anything that says the area over the TDS was sacrificial, and the entry in R&R says it was above the TDS, not part of it. It goes on to express concern that there might be flooding there. As far as I can see, it is only your assumption that this was designed as part of the TDS, and not backed up by any authoritative source. That is true, is it not? It also says the TDS itself was larger than in Nelson in order to provide for the expansion of blast. This characteristic replaced the outboard vent arrangement on Nelson, which was considered to be not terribly effective.

R&R lists splinter protection. Why do you think they excluded the weather deck from that? I think it's because it wasn't considered to have anything other than structural characteristics any more than any other structural steel does. Are you now going to say the entire ship was made of splinter protection?

[dunmunro]

R&R lists splinter protection. Why do you think they excluded the weather deck from that? I think it's because it wasn't considered to have anything other than structural characteristics any more than any other structural steel does. Are you now going to say the entire ship was made of splinter protection?

I would suggest you also take that up with Nathan Okun. Both the USN and RN used D steel or STS for the weather deck and ships sides. This provides splinter/strafing protection to the ship above the citadel. Page 10 of R&R has a brief discussion of protection provided by different types of plating.

This images clearly shows that the RN considered the upper deck as part of the armour scheme:

[dunmunro]

I've never seen anything that says the area over the TDS was sacrificial, and the entry in R&R says it was above the TDS, not part of it. It goes on to express concern that there might be flooding there. As far as I can see, it is only your assumption that this was designed as part of the TDS, and not backed up by any authoritative source. That is true, is it not? It also says the TDS itself was larger than in Nelson in order to provide for the expansion of blast. This characteristic replaced the outboard vent arrangement on Nelson, which was considered to be not terribly effective.

This image clearly shows that the space above the SPS was to be used for upward venting:



R&R on p293, discuss the differences between the Nelson and KGV SPS systems. Nelson's system was designed to vent outboard of the citadel, whereas on KGV it was designed to vent inboard. Now if it vents inboard, it can either go into the ship and destroy the 38mm - 44mm SPS holding bulkhead, or it can go upward, through the 7mm deck over the SPS V-L-V layers. You will note that the holding bulkhead extends upward to cover the compartment directly above the SPS. The recent survey of the PoW, Death of a battleship, also notes that the torpedo hit abreast B turret vented upward. The RN tested the SPS design with a full scale, 1000lb charge, and one look at the cross section of the SPS makes it instantly (and painfully) obvious that the system will vent upwards through the 7mm deck. Since the job 74 trials were done prior to construction, it is completely obvious that the system is designed for upward venting.

[dunmunro]

G&D come very close to stating what I'm saying on page 295 of Allied BBs where they discuss the differences between Vanguard and KGV:

"The most important changes were the redesign of the pumping system... for the protective layer and the removal of the washrooms over the SPS. It was accepted that the original washrooms had to be considered spaces where the pressure wave could be vented..." It goes on to state that the washrooms were moved elsewhere and the original washrooms spaces were subdivided by extending the SPS bulkheads one deck higher and these compartments were now void spaces, although a deck still separated the V-L-V layer from the original washroom spaces.

Of course G&D make it sound as though the KGV designers somehow believed that a 7mm deck between the V-L-V layer could prevent a torpedo hit from venting upward, which is nonsense, as the KGV designers simply accepted that the washrooms and other compartments above the SPS would have to be sacrificed in the event of a torpedo hit. On Vanguard, space was found to convert these compartments from sacrificial spaces into voids, which could then be further subdivided.

[Dave Saxton]

You can not equate Ducol with STS/Class B or other types of RHA (rolled homogenous armour).

[Thorsten Wahl]

see following extract from the german splinterprotection charts for AP(PsGr.) and HE (SpGr. Kz projectiles against Wh.
from non ballistic materials you can expect less protection

from this table you can derive that 25 mm splinterprotection is somewhat too low against main caliber projectiles

[Dave Saxton]

I recall that graph now Thorsten. This is very important information pertaining to the application of splinter protection. A non ballistic (or semi ballistic) material could be made more effective gegen splinters by making it exceedingly hard. The trade off would be decreased toughness and ductility that would make it less usefull against larger caliber ordnance.

But, we need not quible over whether or not this material has a significant effect on the deck protection of British battleships, even allowing 90% ballistic protection of RHA, because it will still be subject to Krupp's and/or the USN's rules pertaining to laminates.

[Thorsten Wahl]

This images clearly shows that the RN considered the upper deck as part of the armour scheme:

but its not included in the immunity calculations,
on the other side the 50 mm Oberdeck was also not a part of the calculation, but it has definately some influence on finalballistics at oblique impacts at 60deg and over.

and this influence is also given to the american superheavies to an probably greater extent because of greater lenght of the projectile compared with the "lightweight Nelson shot"

[Dave Saxton]

Krupp found that extra length per caliber becomes a serious liability during oblique impact if the cap is removed. This is where a ballistic material (non laminate) upper deck of sufficient thickness to de-cap has significant influence on the overall deck protection. The British found that the Tirpitz design always removed the cap of large caliber APC. These effects can be further augumented by using an homogenous resistance plate of more than 80kg/mm2 tensile.

The Japanese excluded D-Steel structural componants and laminates from their effective thickness calculations as well.

[JamesGDB]

Excellent information on this forum...I do think the IOWA has clear advantages over Bismarck and really would not even be a good fight, Iowa would engage at range with use of her Radar, Bismarck would if possible try to escape.

Hard to compare a mid 1930's design to a more modern 1940 design. In wartime every upgrade is crucial, and the ALLIES after Pearl saw the need for extra AA protection, and heavy Armor protection vs bombs.
I also have been just roaming around these formus for awhile and cant figure out why people compare the Main armament incorrectly when it comes to Bismarck.

for example Rodney 45 calibres long, /45 in shorthand, meaning it was 45 x 16 inches = 720 inches long. Bismarck Barrel length (L/52)772.834 inches: Bore length (L/48.5) (Correct)

Anyways just interesting that I have seen many people compare the Calibre length of Allied ships to Bismarcks "Bore" length. Not sure how many other people noticed this.

[yellowtail3]

I also have been just roaming around these formus for awhile and cant figure out why people compare the Main armament incorrectly when it comes to Bismarck.

because it's been wrong in a lot of sources for a loooooong time, is the likely reason

(this coming from a guy with no first-hand experience with anything bigger that 5"/54cal)

[Hartmann10]

for example Rodney 45 calibres long, /45 in shorthand, meaning it was 45 x 16 inches = 720 inches long. Bismarck Barrel length (L/52)772.834 inches: Bore length (L/48.5) (Correct)

Bismarck´s barrell lenght as indicated by German sources is completelly correct (It is, 52 calibres,) the main problem is that Germany tended to use the measuring system of all the bore plus the chamber (that is, 48,5 calibres + the chamber = 52 calibres) and the US NAvy used only the bore lenght.

JamesGDB wrote:
I also have been just roaming around these formus for awhile and cant figure out why people compare the Main armament incorrectly when it comes to Bismarck.
because it's been wrong in a lot of sources for a loooooong time, is the likely reason

In this case, there is not wrong sources, only different ways of meassure the barrel lenght.

Hope this helps

[rosspest]

The Iowa was probably the better ship, but the Bismarck was also a fine ship, and her brave crew fought to the end against overwelming forces.
The problems that led to the Bismarck's sinking would likely not have plauged an Iowa Class.
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.
2 50% more range. An Iowa would not have had to slow down to conserve fuel, on the run to Brest, allowing the Ark Royal to catch up to it.
3. Much better Anti-Aircraft. American battleships were often swarmed by as many as 2 dozen Japanese aircraft. One was attacked by 29 airplanes in a single attack. The South Dakota shot down 26 airplanes in one day. The slow Swordfish would have had no chance, against an Iowa's 20-5", 80-40mm, and 49-20mm guns. All 10 American battleships built after 1940 survived the war. The Bismark barely lasted a week.
4. Better rudders, in a side by side arrangement, rather than one in front of the other.
It is a little unfair to compare a 1941 ship against a 1944 ship. The Americans and British also had the advantage of using German battleships for target practice after WWI to see what armor arrangement worked better.
In a close in fight, with an Iowa's radar disabled, it would have been a real battle, because that is what the Bismarck was designed for.