The Illustrious class was a class of aircraft carrier of the Royal Navy that included some of the most important British warships in the Second World War. They were laid down in the late 1930s as part of the rearmament of British forces in response to the emerging threats of Nazi Germany, Fascist Italy and Imperial Japan. The later two ships of the Implacable class were also built to modified designs to carry larger air wings. Implacable and Indefatigable both had two hangar levels, albeit with a limited 14-foot (4.3 m) head room.