By the end of 1942, German U-boats were seemingly on the verge of controlling the Atlantic shipping lanes. In the summer of 1942, the Allies 1ost 348 merchant vessels to enemy "wolf-packs." However, new anti-submarine tactics and equipment slowly began to turn the tide in favour of the Royal Canadian Navy (RCN) and Royal Navy (RN).
Much of the Allied success was due to improved methods of submarine detection. Corvettes and destroyers were equipped with improved ASDIC (a type of sonar) and radar that could detect submarines cruising on the surface at night or in dense fog banks. Both navies had also developed techniques for using U-boat radio transmissions to pinpoint the locations of enemy submarines. At the same time, the Allies had established airbases in Greenland and Iceland that allowed anti-submarine patrols to cover a far greater portion of the main shipping routes. Aircraft could easily spot U-boats, even when they were submerged at periscope depth.
By 1943, most escorts were also armed with new "hedgehog" anti-submarine ordnance. The hedgehogs could launch up to 24 small depth charges over a wide area and proved to be devastating weapons against German submarines once they had been detected.
By mid-1944, the German U-boat fleet was losing more vessels than Allied convoys were merchant ships. In the last six months of that year, the Allies lost only eight ships to German U-boats. The Battle of the Atlantic had been won. In the last weeks of the war, the German navy was about to introduce a new series of U-boats that were so advanced technologically that they would certainly have tipped the scales in Germany's favour, but the war ended before they could be put into service.