I like to classify american battleship design like this: the standard dreadnoughts like the USS texas to the Colorados at 21 knots with 4 turrets so that one blown turret will not affect loss of fire output.
Then you have the fast battleships which sacrificed one turret for more speed, the north carolinas and south dakotas with 27-28 knots.
Afterwards you have the super battlecrusier at Iowa at 32.5 knots and super dreadnaught at montana. 28 knots planned.
I call the Iowa super battle cruisers as their armor is not that great and that her torpedo bulkheads are internal as with most US BBs. These bulkheads do perform worst than the bluges that were use in the Yamato, North carolina refits, planned montana, fuso refit, nagato.
Why this matters is that torpedo bulkheads are internal, bulges are "external" meaning by penetration, you lose a lot more buoyancy. i.e. intetral bulkheads are designed for speed, bulges are designed for survivability.
Iowa had an inclined at around 70 deg 307mm internal belt and a water line armor of 37mm. Weather deck armor was 37mm with a 121mm main deck for a total of 158mm.
Bismark however had 320mm vertical armor at the waterline, 110mm sloped armor like in a protected crusier at around 40 deg and a 45mm bulkhead. Deck armor is 50 mm weather deck, 35mm inner deck and 80mm main armor deck for a total of 165mm.
That means line of sight armor to the protected area of the ship is around 367mm for the Iowa and 537mm for the Bismark. One should note that the Iowa 37mm waterline armor can be penetrated by 100mm guns of destroyers (and secondary guns) and it will cause flooding of torpedo bulkheads. Flooding will only occur in the bismark after the penetration of the 320mm main belt. even 8" shells from the Baltimore at 10 km and at right angles will not penetrate. AP Mark 8 from the 16"/50 Mark 7 on the iowa can only penetrate this at 15K yards (14KM) for 585 (around 16km est). The 38 cm SK C/34 on the bismark can penetrate 393mm at 22 km (so around 24km).
Plunging fire on the Iowa main belt wins due to the incline. then again even if the incline belt is not penetrated, the shell will flood the torpedo bulkhead. But for deck armor, at 35kM the bismark can penetrate 170mm deck armor while at 30K yards (27km) the Iowa can penetate 169mm and 35K yards (32km) 215mm, so around 29 km or more to penetrate the Bismark.
Thus the zone that iowa want to fight bismark is greater than 29 km to 35 km for imunity. While the bismark wants to fight the iowa between 24km to 14km for immunity.
And we all know straddles at that range is rare, Iowa and new jersy straddled nowaki at around 35k yards, no hits. Scharnhorst hit Glorious at 24 km, Warspite hit Guilio Cesare at 24 km, Yamato could have straddled Gambier Bay at 35 km. hood was sunk at around 14 km. i.e. the battle favors the bismark if it is a 1v1. especially, german radar technology is not bad either.
Iowa can dictate the battle due to her speed. but speed will be lost when the torpedo bulkheads gets flooded by the splinter damage of long range gun fire.
my 2 cents.
