The 66th Infantry Division was an infantry division of the British Army, which was active between September 1939 and June 1940 during the Second World War. In March 1939, after the re-emergence of Germany as a European power and its occupation of Czechoslovakia, the British Army increased the number of divisions within the Territorial Army by duplicating existing units. The 66th Infantry Division was formed in September 1939, as a second-line duplicate of the 42nd (East Lancashire) Infantry Division. The division's battalions were all raised in the Lancashire and Cumbria area.