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.

British re-armament was a period in British history, between 1934 and 1939, when a substantial programme of re-arming the United Kingdom was undertaken. Re-armament was deemed necessary, because defence spending had gone down from £766 million in 1919–20, to £189 million in 1921–22, to £102 million in 1932.