The Endicott Board had an RTL choice between Krupp, Skoda and Vickers, Armstrong in 1885. I simply flipped the choice and went for wedge breech blocks and Krupp mortars. US gun-makers had to go metric IF they chose Krupp instead of Vickers. British pattern guns were chosen at the time because... well it was the BRITISH. (See remarks about Navy see, navy do, a bit further along.). From such simple choices come huge butterflies. It works out that the Americans would have gone metric if they chose Schneider Canet as they would for their field guns after WWI.3 main turrets on a pre-dreadnought? Has that ever been actually tried? Because from what I know all pre-dreadnoughts had only two main turrets.
The Kurfürst Friedrich Wilhelm class carried 28cmL40 and L35 guns.I love the model. It still looks like they should have carried the forecastle deck about 100' further after so they could superpose the rear turrets, but I guess that would do bad things to the stability. One question - why are your 1890s American designers/shipbuilders working in metric? I don't think the OTL US had any metric-calibre guns in that period.
The Germans don't seem to have been particularly happy with the Brandenburgs. They built them with 6x9.4" and a very light secondary armament - I guess that middle turret ate up a lot of the midships space - but for the next two classes they dropped the main armament to 4x9.4" but added a very heavy secondary armament of 18x5.9". Then they went to 11" for the main armament but kept the heavy secondary battery (14x6.7").
This was also known as the Brandenburg Class.
The Germans were unhappy with the amidships gun mount because they discovered that the blast safety zone narrowed the broadside arc coverage of the amidships turret to less than 50 degrees per beam. If they tried to angle fire further forward or aft outside that narrow arc, the muzzle blast killed exposed deck crew and severely damaged superstructure, such as the ridiculous catwalk they mounted as a bridge over the amidships gun-house. And... The 35 caliber guns also had different throw ballistics and shell flight profiles than the end chaser guns. Not all the guns could be counted to use the same shooting elevation and bearing train. The American ATL Iowa has wider arcs because of no intervening superstructure deck clutter or crew running around on the quarterdeck.
The forecastle break is a result of the start model. I kept the mistake, because I did not want a wank Yank, just a tank Yank who would be a bit better than the floating Spanish American War DEATHTRAPS that were the New Steel Navy. Those American ships were horrible sea-keepers and fighting platforms. At least with this mod, they would not roll over and blow apart if one looked at them funny.
As for the secondary guns: the Germans observed how the British designed the Majestics. German see. Germans copy. The French will do likewise and so will the Italians and the Japanese. In the RTL the Americans do the same. In the ATL, the Americans do a KFW because it seems a logical layout for a broadside battery based on their own experience with American civil war monitors. They just are a bit smarter about it. From their American civil war experience they know about muzzle blast, exposed gun crew, blast safety zones, damaged superstructure and so forth. In the RTL, before they try super-positioned and super imposed gun turrets, they will experiment on a monitor to make the ideas they have work. In the ATL, this happens before the first American battleships are laid down. The extra two gun barrels also hides the RTL/ATL fact that they do not have quick fire guns and smokeless powder yet.
But why change the choice from inches to centimeters in guns one might ask? There are a couple of good technical reasons I can suggest; Vickers guns had a nasty habit, like the French Schneider guns of blowing out the breech block and KILLING the gun mount, wrecking the tube and the crew that served the gun, as the Spanish will discover in battle when they try full warshots with their defective Vickers and Schneider export guns, while also wiping out adjacent positions with spall and burst barrel breech fragments. This happened in the period with such regularity that it was an accepted hazard in the French and British navies.
Krupp guns had a unique reputation for safety in the era. When their breech blocks failed, it was a deadly gas blow back which killed the gun crew when the lead seals failed. The breech could then be manually opened by the next gun crew, the damaged button case could be mechanically pried out with the extractor and the gun replaced back into service after swabbing. Of course there was the lead gas problem, too, but that is why the Americans will invent gas masks and ventilate their gun positions. *(Yes, the USN invented primitive gas masks and those weird buttons on top of USN gun houses are VENTILATORS to vent normal poisonous brown powder gunpowder gasses from the propellants they use.).