By 1944 the battle between the Royal Navy and the German U-boat fleet had turned heavily in favour of the British. Advances in British counter-U-boat tactics included superior radar technology on ships and aircraft, small fast vessels formed into hunter-killer groups, which would actively seek and pursue U-boats, and the ability to crack the German Enigma codes. Altogether these began to prove highly effective in reducing Allied shipping losses whilst maximizing U-boat kills. A naval blockade of the English Channel during the D-Day landings and the following naval supply operation was successful at blocking all German U-boats from entering the Allied crossing area for the first two weeks of the operation. Towards the end of the war, Germany’s U-boats were becoming increasingly technologically obsolete and the plan of attack favoured by Admiral Dönitz focussed mainly on deploying U-boats in large numbers rather than developing new approaches to the superior allied tactics.
— OR —