A treaty battleship was a battleship built in the 1920s or 1930s under the terms of one of a number of international treaties governing warship construction. Many of these ships played an active role in the Second World War, but few survived long after it. The strict limits on displacement forced the designers of battleships to make compromises which they might have wished to avoid given the choice. The 1920s and 1930s saw a number of innovations in battleship design, particularly in engines, underwater protection, and aircraft.