this might be dumb sounding, but was there suc…

this might be dumb sounding, but was there such a thing as a small ship with a massive gun with the purpose of fucking battleships up? it sounds like a interesting concept but idk how realistic it'd be

Why yes, yes there were! Meet the Royal Navy’s take on the american monitor concept!

Erebus-class monitors, armed with a pair of BL 15 inch Mk I 381mm guns.

Marshal Ney-class monitor, same armament as the earlier class.

Abercrombie-class monitor, armed with a pair of 14"/45 356mm guns.   

Roberts-class monitors, same armament as the Erebus and Marshal-Ney classes. 

And the somewhat infamous Lord Clive-class monitors, featuring monstrous BL 18 inch Mk I 460mm gun.

All of these ships were intended for the coastal defense role, as in, to be able to stand against battleships via their firepower alone, using their relative diminutive size as an offset of their virtual lack of armor.