Battleships also gave support gunnery (that is: shooting targets on coast or inland) for amphibious invasions. They often served as flagships. However, their main role was to limit the enemy's use of the seas for whatever purpose. The value of the battleship had been questioned, even during their heyday. During World Wars I and II, the activity of the German surface fleet was limited by the Royal Navy, which had more battleships. On the other hand, submarines and planes could be produced in quantity, and they became more important in naval warfare. There were few decisive fleet battles between battleships. They were vulnerable to the smaller, cheaper weapons: the torpedo, the naval mine, and later aircraft and the guided missile.