Can I list a few?
Aircraft carriers would probably be my first choice due to the rise of air power. They essentially made dreadnought-centered navy strategy obsolete. Probably the biggest impact on naval combat than any other ship, I imagine.
U Boats get my vote for ingenuity and stealth. Germany worked around it’s inferior surface ships and kept the Allies on their toes in the Atlantic without conventional engagements. I’d pick type XXI as top choice due to it’s ability and that I think it looks pretty damn nice.
Last I’d got with Higgins boats for their production and utility. I don’t think there was a better boat for beach landings, and they were produced very quickly in a large quantity.
And the DUKW for honorable mention in the weird category. :mrgreen: