The squadron became operative on 20 April 1943. Three days later a detachment was sent to RAF Scatsta in Shetland. The role continued as before, with submarine sweeping, patrol and reconnaissance, as well as meteorological surveys. They regularly patrolled the areas between Shetland past the Faeroe Islands to Iceland. Also active in the area was the Norwegian 333 Squadron and other RAF squadrons. The Sunderlands would on occasion partake in aerial combat with German fighters. Following the Allied Invasion of Normandy in June 1944, German submarines increasingly moved northwards and the 330 Sqn intensified its sweeping. From August the German tactics changed and the 330 Sqn's patrols moved steadily closer to Norway.