[rjsw]

> I suspect modern armor piercing rounds on a 4.5" gun might do better than you expect against 1918 battleship armor.

Not sure they would. The standard RN small ship gun in WWII was 4.7". The standing orders if a Captain of a small ship sighted a German battleship was to load armour piercing rounds and aim for rangefinders or radar antennae, there wasn't any expectation of doing much damage to elsewhere on the target. His relatives would get given his posthumous VC some time later.

There are youtube videos of using modern torpedoes on ships. One should be enough to sink anything, particularly if it detonated under a battleship magazine.

You could also compare the effects of early guided bombs on battleships [1], they were comparable in weight and warhead to modern guided bombs and to things like the Harpoon missile.

[1] https://en.wikipedia.org/wiki/Fritz_X

[mcguire]

I love the term SINKEX (sinking exercise):

https://www.youtube.com/watch?v=uXk8JAQ-370