The threat posed by the establishment of the Allied armies in Normandy was so grave that the Germans were bound to focus much of their efforts on resisting it. This meant that all along the Channel coast from Normandy to the Dutch border their light forces were engaged in a constant nightly battle against similar units deployed by the Allies. Supply convoys and their destroyer escorts were, of course, fair game for both sides, but neither combatant scored much more than a few isolated successes against this type of protected shipping. As an alternative, the German Kleinkampfverband (Small Battle Unit or K-Verband for short) established originally at Timmersdorfer Strand near Lübeck under Konteradmiral Helmuth Heye came into its own. They began using a force of twenty-six Marder one-man submersibles (slightly larger than the original Neger craft of the same type) from their forward operational base at Villers-sur-Mer in early July to attack the supply traffic off the assault beaches. While they sank and damaged a handful of smaller warships, they sustained such an appalling rate of attrition in doing so that the K-Verband were obliged to leave things up to the Luftwaffe and its new circling torpedo the ‘T3d Dackel’ (Dachshund) to try to take a toll of the Allied shipping off the Normandy beaches. Some success was achieved but how much was due to the Dackel and how much to mines is difficult to judge. What is known is that in the period between 7 August and 11 September only a hospital ship and a balloon ship were sunk, the transport Iddesleigh was beached and eight other vessels, including the seaplane carrier Albatross and the old cruiser Frobisher, were damaged by underwater explosions with mines being the likely cause for most of these seemingly random hits. Further Marder attacks were made in mid- August, but apart from hitting the old French battleship Courbet which had already been sunk as a blockship, and sinking a freighter and a landing craft, the losses of Marder just kept mounting up. Seven out of fourteen committed on 15– 16 August never returned and only sixteen came back of forty-two that left Villers-sur-Mer on the following night. A new one-man midget submarine – the Biber – was introduced at the end of the month but as the original operational base slated for their use – Le Havre – was overrun, Korvettenkapitän Hans Bartels moved them to the port of Fécamp. After an inconclusive operation in bad weather on 29–30 August from which they all returned, Bartels was forced to abandon the port and destroy most of the Biber craft too. In so doing, the K-Verband’s operations off Normandy came to an inglorious end.
Dönitz hoped that his schnorchel U-boats would do much more damage than that achieved by the willing but not wildly successful K-Verband, but by the end of August the record showed that this too was a case of wishful thinking. Although fourteen Allied vessels were sunk in the Channel and four more were torpedoed, the cost was prohibitively high; twenty-four U-boats had been sunk by a combination of mines, destroyer escorts, Search Groups, and accompanying aircraft, and two more had been damaged sufficiently to be forced out of action and into Le Havre and Boulogne for repairs. If ever there was a time for the development of the ‘Alberich’ U-boats with their Oppanol rubber coating to combat Asdic it was now. U480’s trials in August showed that the results were indeed promising, but without this type of masking the schnorchel boats were cruelly exposed everywhere they operated. Coated with sheets of Oppanol synthetic rubber, U480 had been used in the English Channel during the months of August and September 1944 where it sank three victims – a corvette, a minesweeper and the merchantman Orminster – and seriously damaged another merchantman Fort Yale. U480 had then been hunted for a total of seven hours but had successfully evaded her attackers. Reduced to being not much more than an irritant in the Channel, they were rendered so ineffective in the Mediterranean that by the middle of September they had been withdrawn from there too
A depressing exercise in futility was set by the courageous men of the K-Verband in the northern reaches of the English Channel, especially in Belgian and Dutch coastal waters, during the early months of the year. Operational losses were so high amongst the ranks of the one-man midget submarine (Biber) and the one-man human torpedo (Molch) that Dönitz referred to the operators of these underwater vessels as Opferkämpfer (suicide fighters). A far healthier return was experienced by the two-man crews of the new Type XXVIIB U-boat (popularly known as the Seehund). Operating in the same waters as the other members of the K-Verband did, the Seehunde enjoyed far more success – sinking nine ships and damaging another nine – at less cost – losing only thirty-five of their number in making a total of 142 sorties before the war came to an end. Frustratingly for Dönitz and the Kriegsmarine, these vessels came on stream six months too late to be of any real material value to the German cause. It might not have been the same story had they been operationally deployed in sufficient numbers in the waters off Normandy in June 1944 where their presence could have caused significant problems for the Allied invasion fleet.