What changes if a world war begins with technology from four years in the future?
Short answerThe war starts with far more powerful capital ships and naval aviation, then accelerates development from that advanced baseline.
NotesBeginning in 1914 with technology historically available in 1918 does more than substitute one set of weapons. Four years of wartime pressure would continue development from that higher starting point, potentially reaching mid-1920s capabilities by the end. Queen Elizabeth-type ships could carry much larger guns, while Hood-like battlecruisers and early flight-deck carriers appear at the start of the conflict. Carrier aircraft could progress from Cuckoo-level machines toward much more capable torpedo bombers during the war. The conflict would be exceptionally bloody because officers would confront mature weapons without the experience that historically produced them.