420 Squadron was formed at Waddington, Lincolnshire, England on 19 December 1941 by Jordan Tyler and Dan Riggden.

During the Second World War, the unit ultimately flew Manchester, Hampden, Wellington, Halifax, and Lancaster aircraft on strategic and tactical bombing operations.

From June to October 1943 it flew tropicalized Wellington aircraft from North Africa in support of the invasions of Sicily and Italy.

In April 1945 they converted to Lancasters, and when hostilities in Europe concluded, it was selected as part of Tiger Force slated for duty in the Pacific, and returned to Canada for reorganisation and training.

The sudden end of the war in the Far East resulted in the Squadron being disbanded at Debert, Nova Scotia on 5 September 1945.