1zseni

That's certainly a major problem, but the not the main reason. In the 1920's the Japanese made extensive gun test on the unfinished and scrapped battleships (Washington Naval Treaty). What they found was that shells that hits the water and passes under the main belt, penetrating the underwater protection can do extensive damage. So they modified their AP shells to be able to do this with more success and even their underwater protection. So their main tactic was to hit the water and penetrate the underwater protection, while reinforcing their own ships against this. if you think about it's kinda crazy that they made their whole plan around this, when they could not guarantee it would happen in real battle. So this is the answer. The Yamato's underwater protection wasn't made against torpedoes, it was made against AP shells, hence the thick armor. the Yamato class could withstand so much torpedo damage because of the sheer size of the ship, and buoyancy. If you wish for, here is the source, but it's Hungarian.... http://acelmonstrum.host22.com/mus.html#5

GK doesn't have turtleback? What? Why? They made it an all-or-nothing ship? Or what do you mean?

What the others said before me. The Bismarck class was made for close range engagements, its belt armor with the plus citadel armor is equal to around 600mm effective armor (if the incoming shells vector is 5 degree or less), so in close range it's actually better then Yamato's. (Yamatos getting better if the vector is 20-25 degree or higher). On the other hand the deck armor is relatively vulnerable in long ranges, if you only take the armor thickness into consideration. (So if a shell hits it 30+ degree, it only has to penetrate around 250mm or less armor) Or you can just spam HE, and burn it down.