A 150,000-ton battleship can be built but may only be a showpiece

Could a fictional navy with 1950s-equivalent technology build a 150,000-ton, twenty-knot battleship armed with twelve 21-inch guns?

Yes in physical terms, but only sound turret, ammunition, machinery, and reliability engineering would make it more than a prestige showpiece.

The question comes from a fictional nation roleplay using technology comparable to the 1950s. Its ruler demands a 150,000-ton battleship making at least twenty knots, later specified with twelve 21-inch guns in four triple turrets. The panel considers that scale physically possible, though likely to produce a prestige showpiece. Combat usefulness would depend on adequate turret space, powered machinery, a robust reloading system, and engines built for reliability. The stated German-derived gun concept is accepted as workable but slow-firing, with a screw breech preferred. A later clarification identifies that mechanism as an interrupted-thread design. The fictional state's political demands explain the excessive size; they do not guarantee that the completed ship would function well at sea.