The Squadron was formed as part of 5 Group on 21 March 1943 at Scampton by Wing Commander Guy Gibson with 18 elite volunteer crews. They were equipped with Lancasters with the sole intention of smashing the Ruhr dams (on 16/17 May). After the successful raid, Arthur Harris decided to let 617 stay in 5 Group making them ". . . a special duties squadron. They needn't do ordinary ops", he said. On 30 August they moved to Conningsby and then on 1 January 1944 to Woodhall Spa where they stayed until the end of the war. Under the guidance of a series of famous Wincos, including Leonard Cheshire, and with the active encouragement of Air Chief Marshall Sir Ralph Cochrane they developed skills in pin-point target marking using Mosquitoes and Mustangs eventually leading the Pathfinder Force. Later their aircraft were modified to take Barnes Wallis's Tall Boy and Grand Slam bombs which did so much damage to the U-boat pens, bridges, V1 and V2 rocket sites and sank the Tirpitz. The men of 617 won over 150 decorations.