Warship efficiency depends on what the ship achieved for its cost

What were the least efficient warships of World War I and World War II?

Hexagonal pre-dreadnoughts and the Courageous family are candidates for World War I, while Shinano is the strongest World War II example.

For World War I, hexagonal pre-dreadnought layouts are offered as inefficient because their gun arrangement imposed heavy structural costs for limited effective fire. Courageous and Furious also enter the discussion as expensive ships whose original concept struggled to justify itself. For World War II, Shinano is the clearest suggestion because an enormous conversion produced almost no useful service. Late German construction is mentioned more broadly, but the exchange remains an off-the-cuff comparison rather than a measured ranking with one fixed efficiency formula.