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Japan 51 cm/45 (20.1") "A" Type 98 (?) - NavWeaps The bursting charge of the 20 inch HE shell intended for the A-150 'Super Yamato' would have been 84kg. Not... hundreds of kg. There are actual data and formulae on how much armor is required to defeat an HE shell. Okun Resource - Miscellaneous Naval-Armor-Related Formulae - NavWeaps This formula suggests that a 20 inch nose-fused HE shell could, at most, assuming a point blank impact at 90 degrees at 2300 fps (basically muzzle velocity), blow a 20 inch hole in a 6.8 inch plate of STS homogeneous armor, and that a 8.16 inch plate is the maximum thickness that would be cracked or dented. (Yes, I realize that the armor in the game would be face hardened, but I don't think it makes a huge difference here). Based on this I would expect a 4.6 inch plate to end up with a ~30 inch hole. As for the 25 inch belt... I wouldn't expect any damage at all. This is generous as we're not talking about point blank, 90 degree impacts, this was an engagement at around 20 km where the shells would be striking much closer to 45 degrees and would been slowed by air drag. There's a reason that AP was used - HE is just not very effective against heavy armor. If HE shells were able to cause significant, incapacitating damage to battleships without penetrating, battleships would have been built with very different armaments and protection schemes. In no way should 11 20 inch HE partial penetrations (several of which hit the strongest part of the protection scheme - a protection scheme far stronger than any ever constructed) be able to put a 75,000 ton battleship in serious danger of sinking due to structural damage. Battleship protection schemes were designed to protect propulsion, steering, the main armament, ammunition, and enough reserve buoyancy to keep the ship from sinking from anything short of an AP shell, AP bomb, or torpedo that was actually powerful enough to penetrate. From HE shells, I would expect damage to the less armored areas, and a superstructure hit to seriously mess up fire control and spotting, but currently in the game, you can *sink* a battleship with HE without ever penetrating its armor. There is no way that is reasonable.

The numbers are correct. They are shooting HE (yellow tracers), and HE has very low effective pen (only around 7 inches for 20 inch HE shells). If they were shooting AP we would see over 20 inches of effective pen, and they would get full penetrations against belt extended/deck extended. They are hitting my armor which has between 9.2 and 50 inches of effective armor, so averaged out among all the hits 27.7 inches of effective armor is realistic. On the other hand, against their ship, I am shooting 18 inch AP against relatively thin armor (and penetrating it), so I'm getting 22.8 inches of effective pen on average, against an average of 10.9 inches of effective armor. I think the reason I have more fires is I have twice as many hits, and they are actual penetrations which seem to cause more fires.

This is true historically... but it's not the way armor layouts work in the game. There is no upper belt, no torpedo bulkhead, no main deck and armored deck, no armored bulkheads - there is no citadel that conforms to the layout of your main armament - there is just a box... the middle 3 sections of your ship have whatever you specify as the 'deck' armor on top, and whatever you specify as the 'belt' armor on the sides. The outer 2 sections on either end have whatever you specify as the 'deck extended' on top, and whatever you specify as the 'extended belt' on the sides. This is always the case. The different citadel types have no effect on this - all they do is change costs, weights, armor strengths, and probabilities as specified in the tool tip. The armor values in these sections is the only thing that impacts whether you get a mid deck/mid belt/extended deck/extended belt penetration. You'll still get partial AP penetrations, if the shells hitting don't have enough penetration but have a significant fraction of what is needed. However, this isn't really what will get you killed if your ship has extreme levels of armor. If the AI determines that it cannot penetrate your ship, it will shoot HE instead, and HE requires far less penetration to get a partial pen, and larger caliber HE shells do huge amount of damage from a partial pen. A HE partial pen will do far, far more damage than an AP partial pen, which is very unrealistic against heavy armor.

It doesn't seem possible to protect a battleship adequately against guns larger than 17 inches. If you armor your ship sufficiently to resist AP, the AI will always shoot HE, and HE partial penetrations do significant damage, even against very thick armor. The partial penetration damage scales up rapidly with caliber, and once you're facing 20 inch guns, HE partial penetrations do so much damage they can knock out main battery guns that have 50 equivalent inches of armor plate, as well as damage engines behind similarly massive main belts. In this scenario, the enemy super-battleship has dealt almost as much damage with 11 20 inch HE partial penetrations as my battleship has with 22 18 inch AP full penetrations, and has knocked out two engines and a main battery turret. As a side note, the power of these HE shells also means you cannot go the all-or-nothing method, even if you keep all of your magazines inside the middle 3 sections that are protected by the main belt. 20 inch HE will never overpen and if it actually gets a full penetration in your bow or stern, it will wreck half your ship and splash damage everywhere, including in your main belt sections. You need around 8 equivalent inches of armor protection to prevent a 20 inch HE full penetration.

The easiest way I've found is to start the battle (you can do this as long as your ship meets the minimum requirements), and then look at the ship's diagram. As previously mentioned, the center three sections are covered by the belt. I have found that there are a few hulls where you can actually make a pretty decent AON ship. The Japanese Large Cruiser is one of those - it has more flexibility around superstructure placement than any other hull, and is very long for its actual displacement. The British N3/G3 hull is also viable due to the ability to place the secondary tower very far back in the ship. You can actually build a very unrealistically capable ship on a small tonnage, as the belt and deck seem to form a full box around the middle three sections of the ship (unlike real battleships, where the main armor deck was not the weather deck since an impossible amount of weight would be involved in an armor belt the entire depth of the hull.) Deck and belt armor is also unrealistically light. In addition, all the engines seem to be packed into the middle three sections, and there are no issues with space mixing in magazines with the engines as there would be in real life. Here is a Japanese Large Cruiser which, at 35,000 tons, has 33 knots of speed, a 21.9 inch belt, 14.6 inches of deck armor (+100%), and 6 18" super heavy autoloading guns with TNT bursting charges. This ship has an immunity zone between 10,000 and 17,500 meters against its own guns. Since the idea is the main armored box cannot be penetrated, you don't need to spend extra weight on Barbette or Citadel enhancements. The ship also has excellent turret angles and good balance. But no torpedo protection, as is traditional for large cruisers (looking at you Alaska class) I have not yet experimented with placing turrets near or on the border of the middle three sections. Currently, by placing all turrets completely inside the middle three sections, I have never been detonated except by a point blank 17" penetration of the mid belt, and a torpedo. Penetrations and overpenetrations of the bow and stern sections only seem to cause flooding and sometimes knock out the rudder. It really does seem as if most designs depend on modifiers to reduce the chance of an ammunition explosion, rather than actually preventing shells from reaching vital spaces.