5 inch AP won't penetrate Dreadnought and Super Dreadnought era armor.
5 inch HE, on the other hand, could set them on fire from stem to stern. 6 inch would do about the same.
8 inch AP could do some damage...at really close range. Like ridiculously close range...around 1,000 yards, which for these ships, it like touching each other ranges in daylight, and freaking close at night.
It's Super Effective?Now now, don't be putting in rocks or anything, okay?Yamashirooo!Such misfortune.....after all...Don't worry, big sis. We won't be doing anything like that.Rei-Go Group VS Nishimura Fleet
Snowball Fight In ProgressAwwright! Didja see that, you brats!!Sure.Yamashiro's childishness is dangerous.What we're putting in is---Onee-sama, we'll use that.armor-piercing shells.