Iowa vs Yamato comparison

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Tech Sergeant
Mar 2, 2005
Berlin (Kreuzberg)
Here are my results of the protective armour scheme comparison of both super battleships. Have a read!
Please be kind and tell any errors you encounter. This paper IS NOT INTENDED for commercial use or publication, it´s for You and for discussion. Acrobat reader V 7.0 is required to open the document (17 pages + 5 pages appendix). Excuse grammar mistakes but feel free to correct me anytime.

It seems, as mentioned previously, that Iowa gets the low end of the line in a comparison with Yamato. The better quality of it´s armour (and even this generalization is wrong regarding class A US armour and VH) does not offset the sheer thickness. My renewed version shows that both designs are more equal thanks to the type 91 APCBC problems with the AP-cap. Still, Yamato is in most area´s, except for simple belt penetration superiorly protected.
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It is very interesting but I will be honest with you, it is way beyond my knowledge on battleships. I do applaud you on your effort, well done.
I thought it was right on, and it solidified every thought i have had, Iowa would have to be pretty lucky to win an angagement. One thing i didnt know so much about on Yamato was just how protected the bridge was. That would be a life saver, no matter what vessel (or aircraft) you encounter. The immune zone on Yamato had to be the most impressive thing to me though.

Iowas underwater protrection, espcially in the bow (though yamato had a somewhat similar bow problem) would make it the loser in my book. A near hit at the waterline, much less a direct hit would doom the poor iowa, and Yamatos secondary amrament would play more of a role when or if the close range broadsides came into effect. Even in a battle of manovere, where broadsides were rarely if ever exchanged, i would give the victory to Yamato, with a tight turning radius, and wider immune zones, it would hold all the advantages.
I made a typing mistake in Yamato´s bridge thickness: the sites are 19" as written, but not the roofs, of course (11.8"). I actually calculated with 11.8" but forgot to fix it in the text.

In a close engagement (10.000yrds and less), I would give Iowa a slight advantage due to a significant higher secondary battery output and HE shells with more striking power (more HE-ordenance). According to my ww2 BB encounter records, there is a 60% chance after hit #1 that the radar set breakes down. In this view a higher battery output may play a role for Iowa. Both ships vitals are exposed to each others main guns at these distances, so the one with a lucky hit may blew up the other, rendering this scenario very, very hypothetical. Iowa also had excellent maneuvering charackteristics (according to Naval bulletins, DD had to beware of vessels of the Iowa-class because they were more maneuverable than DD´s!), this seems to have something to do with the general hull design (having the center of weight in the rear part of the ship = closer to the rudderforces), no specific advantage for Yamato, only.
I like Iowa, dont get me wrong, but for the battle to get within 10,000yrds, Yamato would have to have started from farther away, and close through its own immune zone, firing the entire way into the close engagement, and most likely hitting Iowa on the way in, diminishing its advantage. The secondary armament, as well as main armament, if damaged would be a huge hinderance to Iowa, and if its vulnerable bow was hit, it would lose the speed, and manouvere advantage it had over Yamato.
Dont forget that the Iowa would still be firing its guns at the Yamato doing its share of damage.

If its one thing that was decisevly proven about the IJN, was their damage control philosophy and practice was almost amaturish.
I second that. Some of the damage inflicted to Musashi at her last battle resulted from serious methodical damage controll problems AND little or no buoyancy/metacentric reserve once the bow was flooded. (a problem which it would share with Iowa.
I have to defend myself if You say "unrealistic". It obviously isn´t the last word but I sourced my basics (datas for armour qualities and ballistics from Nathan Okun as the calculating programs) and am confident that the results aren´t that wrong.
If you find errors or have points, I neglected (all possible), please tell me, so I may fix it.
The largest controverse I expect to come are from the uselessnes of Iowas and South Dakotas so called "decapping plates", greatly reducing their immune zone against belt hits by almost 8.000 yrds! But as You may read, I explained why.
Its hard to quantify the lack of skilled damage control parties on board the IJN warships. What if you increased the lethality of the 16" and 5" shells, without it penetrating the armor?

Remember, once fires start in the superstructure, the efficiency of the propulsion and ammo handling crews will degrade.
In case of Yamato, some but not all DC-centres are in proximity to the bridge, worsening the working environment for leading damage controll crew by exposing them to shellfire. Yamato soon lost ALL her DC officers in her last battle because of this. Iowa places two main DC centres under the main armoured deck (as did Bismarck) and this may play a role. But don´t forget that the pure destructive force (kinetic + chemical) of a 18.1" AP hit is twice of that from a 16" AP hit.
I have a question, the Yamato had the tightes turning circle of all battleships of his type, Is this true? I heard about a 640 m turning circle (really impresive for its size). best regards
This is true. The flask-shaped hull with the centre of buoyancy and center of weight placed comparably close to the main and auxilary rudders made such a tight turning radius possible (there are fotos in the net showing Yamato and Musashi evading bombs, you may verify the turining radius from the wakes). But it should be noted that US fast battleships also had a flask-shaped hull design, allowing for a turning radius well under 800 yrds! So Iowa Yamato don´t differ that much but dwarfing the competition of their european BB´s in this respect.
Really, very interesting the thread. (my congratulations for your work from Iowa and Yamato in pdf, really impressive). Another question, the "Bismarck" battleships really turned very tight I suppose, giving the fact that they carried twin "¿suspension?" rudders (Spanish: "timones suspendidos"), the reverse of other European ships like KGV, with only a single rudder, and with a turning circle very big for its size. Is this true?.
Best regards
I have checked my books to verify this but I couldn´t do. It is true that the DKM BB have two seperate rudders (and three shafted propulsion) while KGV and Vanguard class have a single rudder (but four shafted propulsion). Hull shape is comparable. I wouldn´t easily give an advantage without good statistics, so I cannot answer this question. I do believe that neither class has a significant advantage in turning circle over the other. Three shafted propulsion has a disadvantage but this is offsetted by the twin rudders.
Without the rudders the Bismarck could not turn for nothing, its propellers could not help it turn, but the Vanguard had the advantage there because it had four propellers and thus make it turn much better without the rudder.

Once both rudders are knocked out, ok. But such a case was not foreseen by any BB design. One rudder could be knocked out but the other would -in theory- do it´s job. The torpedo hit destroyed the steering controll for both rudders despite beeing heavily armoured. Such a hit would disable Iowa, Vanguard, even Yamato with it´s seperated auxilary steering rooms (during trials they discovered that the auxilary rudders could not stop turning of the ship once Yamato engaged a turn). However, a four shafted design makes for some redundance in such a case and this exactly was a disadvantage in the specific case of Bismarck.

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