1943 was the turning point in the Battle of the Atlantic, when the balance of forces, technologies and tactics turned irrevocably against Germany's U-boats. The victory thus obtained not only secured Britain's transatlantic lifeline to the United States, but in so doing enabled the vast build up in military forces in Britain necessary to launch D-Day in June 1944. The Allied battle to defeat the U-boat menace was a combined effort by the naval and air forces of several Allied nations, and this is the story of one part of that effort during the decisive mid-war period. Nos 10 and 461 Squadrons of the Royal Australian Air Force flew Sunderland flying boats from bases in Wales and Devon as part of RAF Coastal Command; these two sister squadrons flew long-range daylight missions over the eastern Atlantic, patrolling Britain's southwest approaches. They hunted and killed U-boats transiting between their mid-Atlantic hunting grounds and their bases in Bordeaux, and fought furious air battles over the heaving seas of the Bay of Biscay, against Luftwaffe Ju88 long-range fighters tasked specifically with shooting them down. These two Australian squadrons established a combat record second to none.