What was the point of a German experimental 21-inch gun?

Why pursue an experimental gun as large as 21 inches?

The explanation centres on the attraction of possessing the largest gun, without a clear practical ship to carry it.

The project is connected to Hitler's preference for exceptionally large weapons. Gun development alone does not supply a workable naval installation. The answer questions the practical use of the weapon rather than treating it as a ready battleship armament.