The thing is that a battleship is huge. You can kill a tank with a modern subcaliber penetrator because a tank is literally an armored box. Penetrate that and the splinters etc will kill anything inside.
Shoot something like it to a battleship and you make a tiny hole and maybe break a laundry machine. Sure with enough shells you could disable it but that requires a ton and more of shells.
To damage a ship you don’t only need to penetrate the armor you also need to deliver substantial amount of explosives inside said armor.
Don’t get me wrong. The fleet would be wiped out. But against a BB puny 4.5” does nothing, except maybe when delivering incendiaries to the superstructure. Modern fire control allows it to absolutely wreck all destroyers and smaller though combined with autoloaders.
EDIT: More importantly in order to even have that reasonable penetration chance with 4.5” gun you need to be within few kilometers. And at that distance the 1918 RN is really dangerous. Ideally stay farther than maybe 20km.
> 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.
The problems are less that they don't have armor piercing rounds (which they don't), but that the shell only travels ~870 meters per second and only weighs ~20 kg. The projectile doesn't have the momentum to go through more than a few inches of armor. The British 15"/42 from WW2 had a muzzle velocity not much lower, ~750 mps, and weighed ~870 kg. That could penetrate about 10" of armor at 25,000+ yards or 12.5 miles.
The real change would be the ~20 rounds per minute rate of fire plus modern fire control.
Shoot something like it to a battleship and you make a tiny hole and maybe break a laundry machine. Sure with enough shells you could disable it but that requires a ton and more of shells.
To damage a ship you don’t only need to penetrate the armor you also need to deliver substantial amount of explosives inside said armor.
Don’t get me wrong. The fleet would be wiped out. But against a BB puny 4.5” does nothing, except maybe when delivering incendiaries to the superstructure. Modern fire control allows it to absolutely wreck all destroyers and smaller though combined with autoloaders.
EDIT: More importantly in order to even have that reasonable penetration chance with 4.5” gun you need to be within few kilometers. And at that distance the 1918 RN is really dangerous. Ideally stay farther than maybe 20km.