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The Allied victory over the German U-boats in May 1943 was not the end of the Battle of the Atlantic, but it was the decisive moment. Dönitz fulfilled his promise for his submarines to return to the fray, but never again did they pose as grave a threat. The sea and air escorts and support groups sent out with the convoys and the Very Long Range aircraft patrolling in mid-Atlantic were the keystones of the Allied success and they maintained their predominance until the end of the war. Also, in July 1943, the rate of production at which new merchant shipping was coming out of British and American yards overtook the rate at which U-boats were sinking Allied ships at sea and never afterwards fell below it.

During July and August, further defeats were inflicted on Dönitz's forces along U-boat transit routes in the Shetlands-Faroe Islands gap and across the Bay of Biscay. The offensive in the latter area proved by far the most successful of the two, where twenty boats were sunk between 1 July and 2 August. Many were surprised on the surface at night by aircraft now equipped with both Leigh Lights and centrimetric radar. Also, American escort carriers destroyed the "milch cows" refuelling U-boats off the Azores.

The wolf packs returned to the North Atlantic in September 1943 armed with new acoustic homing torpedoes and improved anti-aircraft radar and weapons. However, attacks on convoys over the autumn achieved only limited success at the cost of a severe mauling by Allied sea and air escorts. Forty U-boats were sunk in the North Atlantic in the last four months of 1943 to add to the twelve lost between June and August. Wolf pack tactics had finally failed. In early 1944, Dönitz concentrated on British coastal waters in the north-western approaches in an attempt to repeat the first "happy time". Unfortunately for the German Navy, three and a half years on, Allied anti-submarine firepower was vastly stronger than it had been in 1940. Coastal Command squadrons from western Scotland and Northern Ireland provided continuous air cover, while at sea several escort and support groups, some with escort carriers, were concentrated against the U-boats which suffered another severe defeat.

For the rest of the war, Dönitz's force was reduced to a harassing role to try and tie down as many Allied naval forces as possible. A prime opportunity for such action came against the ships and landing craft massing in the waters of the English Channel and adjacent coastal areas for the invasion of Europe in June 1944. Most U-boats had by this time been fitted with the Schnorkel breathing device, allowing them to stay underwater for much longer periods than hitherto and making them much harder to detect. However, so numerous were the escorts and so intensive the air and sea patrolling accompanying the invasion convoys that few U-boats reached the fleet. In the remaining months of the war, increasingly successful Allied bombing of factories and assembly ports, which delayed the completion of advanced new types, put the seal on the final and utter defeat of the U-boat.

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