Battleships of the Mark into the 1920s

[Nobody]

Those values are for the turret sides, not the barbette sides. WWI ships had even more reduced barbette thickness below the weather deck.

At least for Bismarck it should be mentioned that 220 mm (8.66") is the thickness behind the upper deck (50 mm), the citadel-armor (145 mm) or the main belt (320 mm). That considered I think its thickness is pretty good, the real weakpoint might have been the above deck barbette armor of 340 mm and the turret armor of 360 mm (max).

Ok I somewhat missed the point than. But it's interesting, that they choose the same thickness for below deck barbette and turret side armor, isn't it?

[Ithekro]

Well for a sense of scale:  In the time from from 1893 to 1919 Rohan has built 24 capital ships with others under construction.  In this same time period the United Kingdom built 87 capital ships.  The United States built 39 capital ships.  Germany had built 43 capital ships.  Even France has built 24 capital ships in that time period.

About half each are predreadnoughts, but still, numbers.