Could a Second World War destroyer gun penetrate a pre-dreadnought's hull?
Short answerPossibly, but only in vulnerable areas; the result depends on the ship's armor scheme and the point of impact.
NotesPre-dreadnought protection varied too widely for a single yes-or-no answer. Some ships concentrated armor in a pattern that approached the logic of later all-or-nothing schemes. A destroyer shell might damage lightly protected portions while failing against the main armor belt or citadel. The decisive variables are therefore the exact ship, range, impact conditions, and location of the hit.