The uncertain paper trail for a French 18-inch-gun battleship

Were any French ships designed to carry the prototype 45-centimeter gun?

Possibly only a paper Richelieu derivative; even its official status remains uncertain.

An evolved Richelieu concept with an 18-inch battery may have existed, though it is unclear whether this was an official design or an enthusiast's study. French work on a gun of roughly 45 centimeters did not necessarily mean that a ship had reached a comparable design stage. By the time such a weapon could be mounted, navies were becoming less willing to procure new battleships. The useful distinction is between developing a large gun, sketching a possible carrier for it, and authorizing a real capital-ship program.