It may seem odd but when Andrew Cunningham went to the Admiralty in October 1943, the primary concern with regard to the German Navy was not the U-boats, apparently defeated utterly in May 1943, but the surviving major warships of the surface fleet, notably Tirpitz and Scharnhorst, both of which, based in Norway, threatened Allied convoys to North Russia. They were fast, well-armed, heavily protected and aided and abetted by U-boats, dive bombers, torpedo bombers and reconnaissance aircraft, and escorted by large, fast, powerfully armed destroyers. The U-boats, effectively defeated in May 1943, had virtually withdrawn from the North Atlantic – and found few pickings in other seas – and were hastily re-equipping with new technology, shipping enhanced armament and devising novel tactics. Cunningham found a largely untroubled sea but conventional boats were re-equipped with the Dutch Schnorkel, a device for prolonging underwater endurance and increasing submerged speed.