After the success of the Ruhr dams raid in May 1943, 617 Squadron was retained by RAF Bomber Command for specialist precision bombing operations. It experimented with new bomb sights, target marking techniques and colossal new 'earthquake' bombs developed by Barnes Wallis, the inventor of the 'bouncing bomb'.
An unsuccessful attempt to bomb the Dortmund-Ems Canal from low level in September 1943 resulted in the loss of five aircraft and the death of the Squadron's new commanding officer. Such missions were not repeated, and henceforth 617 Squadron concentrated on high-altitude precision bombing.
In the run-up to D-Day, the Squadron attacked factories, V-weapon sites and communication targets in France. Its commander, Wing Commander Leonard Cheshire, pioneered a controversial new low-level target-marking technique. The improved accuracy minimised civilian casualties when attacking targets in occupied territory.
In the autumn of 1944, 617 Squadron joined 9 Squadron in attacks with 12,000 lb 'Tallboy' bombs on the German battleship Tirpitz, moored in Norwegian waters. The first two attempts were inconclusive owing to cloud and smokescreens, but on 12 November they found Tirpitz with no protection. Sustaining two direct hits, the ship was shattered by an internal explosion and capsized.
In the last months of the Second World War, 617 Squadron made further successful strikes against the German rail and canal network, coastal defences and previously invulnerable U-boat pens, using 'Tallboys' and the monstrous new 22,000 lb 'Grand Slam' bomb. Right to the end, 617 Squadron maintained its position as Bomber Command's ultimate precision bombing specialists.