This unusual ship was armed with three massive, non-rotating, non-elevating cannons for bombardments. The one time it saw service, the ship was more effective at intimidating its enemies than at hitting them. She was soon rendered obsolete, and converted for other purposes.
What ships were considered "a sin" due to the fact that one could "stand on the bridge wing and spit into the powder handling room". *Quotes are approximate, I don't have access to the reference books at the moment
How about the USS Kearsarge/Kentucky, with double decker turrents later used on Virginia class dreadnaughts?
Ordered but never laid down, this submarine at 125 meters would have been big enough to model at 1:144 scale. And given the unusual propulsion, it might have been quite fast.
Is this that funky WWI German turbine-powered submarine with rotating, reloading, underwater broadside torpedoes? I've got plans for that, by the way, but it isn't mentioned in Conway's so I can't build it...
That's the one. Yes, unfortunately there's not a lot of info on it so getting approved for building would be difficult. You're up.