Why were the Orion-class super-dreadnoughts declared obsolete after the First World War?
Short answerThey were neither fast nor powerful enough to justify retention once newer fast battleships and projected capital ships set the standard.
NotesThe Orions were sound ships for their moment, but the Queen Elizabeth class, Hood, and projected G3 and N3 designs rapidly moved the standard onward. They lacked the speed and firepower needed for the envisaged postwar fleet. Retaining them would consume crews and money without filling a distinctive role. A capable ship can become obsolete through fleet evolution rather than a single technical flaw.