For centuries, battle fleets were challenged only by other ships, but the coming of the aircraft changed all that. With a rapid development encouraged by war, the aircraft soon became a threat, a defence and an indispensable auxiliary. Operating necessarily beyond the range of shore-based air support, the fleets, led by the Royal Navy, learned how to carry their own aircraft, and by the end of World War I the aircraft carrier as we know it today had properly come into being.