What if every Royal Navy battleship present in 1915 became a 1939 Lion-class battleship?
Short answerThe High Seas Fleet would be comprehensively outclassed by faster, heavier-gunned, radar-equipped ships, making any major fleet action overwhelmingly favorable to Britain.
NotesThe scenario replaces British pre-dreadnoughts, dreadnoughts, and super-dreadnoughts with the first Lion battleship design, equipped here with radar-controlled gunnery. Each ship has nine 16-inch guns and a speed of about 30 knots. Four ships in the Fifth Battle Squadron would therefore bring 36 radar-directed 16-inch guns against the High Seas Fleet. The proposed outcome is the destruction of the German battle fleet at long range, with the British ships fast enough to dictate the engagement. Japan and the United States would also face a sudden and overwhelming change in the naval balance.