How different would the Second World War be if the US Navy were allowed to match the Royal Navy ship for ship after the Great War?
Short answerThe treaties broadly allowed parity already; US domestic politics, especially the Senate, prevented the Navy from fully reaching it.
NotesA one-for-one US Navy and Royal Navy ship count would change the Second World War less than the hypothetical implies. The treaty system already permitted broad parity. The binding constraint was the US Senate's unwillingness to provide the program needed to reach it, so the international ceiling was not the main obstacle.