The application of a sloped deck here does not compare with the modern German scarp triangle arrangement. The geometry of the German scarp presents a very different striking angle to any projectile passing through the main belt. And your correct about the thickness and the material differences. The arrangement of the cross section attached really amounts to very little additional armour protection.Alberto Virtuani wrote:Therefore magazines were protected, AFAIK, by a 13" vertical belt + slope or main deck as per Bismarck scheme but with slope and deck much thinner than in the German ship (I don't have the Hood exact figures, I remember something like 2" "mild" steel for the slope.....).
12", 13", 15" belts are not that much, even sloped, when confronted with a modern 15" gun like the Italian 381. The Italian 381 can defeat a 13" belt of WW2 British cemented armour all the way out to 32,000 yards. The British warships here might as well be Renown and Repulse.
Meanwhile the British 15" probably can not defeat the modern Italian battleship's protection (both belts and decks) at any battle range inside of 32,000 yards.
The additional horizontal protection was not added to the main deck over magazines but to the middle deck, thus not improving the protection (in combination with her slope and belt), so I think there was only a very limited immunity for QE's against the Italian 15" during the war.
Such adding of plates to a deck of older battleships was almost futile in any case. The marginal improvement in effective thickness was hardly worth the weight, or the work, involved.
Really WWI era warships, even modernized, had no business engaging in battle with more modern capital ships. Consider the fate of the Hood and the Kirishima.