Which planned but unbuilt capital-ship designs would have been worth completing?
Short answerF3 or a close derivative and a King George V with the new 15-inch/45 gun are leading choices. A Spanish 13.5-inch battleship and the unbuilt Agincourt depend on additional funding or unresolved design questions.
NotesF3 or a close derivative is treated as an attainable alternative that could have followed a different design decision, while treaties make completion of G3 much less plausible. Arming the King George V class with the proposed new 15-inch/45 gun would unify the fleet's gun calibre and provide upgrade possibilities for older ships. Incomparable and the 9.2-inch heavy-cruiser projects remain attractive ideas with little realistic route to completion. A Spanish battleship with 13.5-inch guns depends on finding substantially more money. Completion of the Queen Elizabeth-class Agincourt is another choice, partly because it would settle the competing interpretations of her intended heavy armament.