There are two main reasons for this: improvements in tactics, and improvements in technology. New technologies, such as the Leigh Light, improved training for the British and Canadian Navies, improved air patrols and coastal convoys in American waters all combined to give the Allies effective ways of killing U-boats on both sides of the Atlantic.

In the first half of 1942, the Battle of the Atlantic was dominated by German attacks on shipping along the American coast. With most of the USN's destroyer force diverted to the Pacific or to the Mid-Atlantic, American coastal waters were protected by only a few WWI-vintage patrol craft. The USN refused to implement a convoy system, believing that they didn't have enough escorts to effectively protect convoys. This left most coastal traffic to steam independently, easy prey for U-boats. This was exacerbated by the lack of blackout precautions in the USA. For a U-boat lurking out at sea, coastal traffic would be silhouetted against the bright lights of towns ashore, while the U-boat could remain under the cover of darkness. This led to massed sinkings along the American coast, with the Allies practically powerless to resist. The scale of the disaster, combined with pressure from Britain and Canada, forced the USN to implement convoys in May of 1942. This helped to reduce sinkings of merchant ships, but sank comparatively few U-boats. More effective was the improved air umbrella that came with it. The USN and USAAF stepped up air patrols in coastal waters. Previously, these had been carried out by inexperienced USN/USAAF aircrews, or by unarmed Civil Air Patrol aircraft. With more effective training, better weapons and tactics, American air crews were able to score three kills in the North American and Carribbean littoral, plus a fourth added by the RCAF.

Meanwhile, on the other side of the Atlantic, the RAF was developing new weapons. Coastal Command began to deploy the Leigh Light in June 1942. The radars in use at this time would lose contact with a U-boat at closer ranges. This made effective night attacks on surfaced U-boats impossible, as the attacking aircraft would have no way to actually bomb the target the aircraft's radar had guided it to. The Leigh Light, a powerful wing-mounted searchlight, filled in this gap. This was especially important as U-boats used the cover of night to make surfaced transits of the Bay of Biscay, from their bases in Occupied France to their Atlantic hunting grounds. The RAF also introduced new aircraft depth charges. Before June 1942, the RAF only had converted naval depth charges, or 'anti-submarine bombs'. The depth charges, weighing 450lb, were too heavy for Coastal Command's smaller aircraft. They were also set to detonate at a 50ft depth; this was effective against submerged subs, and helped protect the aircraft from the spray and blast of the detonation, but was completely ineffective against surfaced submarines, the main target of aircraft attacks. The anti-submarine bombs, meanwhile, had only contact fuzes, making them ineffective unless dropped precisely. A new 250lb depth charge, with a shallow 25ft fuze setting, was introduced in the first half of 1942. Unfortunately, when initially introduced, it had problems with delayed detonation, which were not fixed until the start of July. To these must be added a number of minor changes, such as improved camouflage schemes and a shift to higher attack altitudes that made it harder for U-boat lookouts to spot an approaching aircraft. With all of these, Coastal Command could finally become a highly effective anti-submarine force, leading to a number of kills in the Bay of Biscay.

The RAF was not alone in developing new weapons. The Royal Navy had developed the 'Hedgehog' anti-submarine spigot mortar, which threw a spray of anti-submarine bombs over the bow. This allowed vessels fitted with it to attack submarines that were still held in the beam of the ship's sonar. Depth charges had to be dropped over the stern, but sonar was ineffective when pointed astern due to the noise of the ship's own engines. This gave the U-boat space to carry out evasive manoeuvres, which ahead-throwing weapons like Hedgehog eliminated. Hedgehog was unpopular with RN captains, and was rarely used for much of 1942, despite being fitted to ships starting in February 1942. However, the Type 144 ASDIC (sonar), designed for use with Hedgehog, was a significant improvement over earlier designs, and was highly popular. More effective for the RN (and its subsidiary force in the Royal Canadian Navy), was investment in training. Anglo-Canadian doctrine emphasised the formation of Escort Groups. These groups trained and operated together, becoming familiar with how each ship operated and their capabilities. This intense training allowed the RN and RCN to carry out a number of effective, coordinated, attacks on U-boats. An example would be the sinking of U-558 on the 31st July. The submarine was found attempting to attack Convoy ON 115 by two Canadian ships, the destroyer Skeena and corvette Wetaskiwin. U-558 dived deep to avoid contact, going to deeper than 600 ft. To counter this, Wetaskiwin stood off and used her ASDIC to guide Skeena into the attack.