This was the German naval effort to infiltrate significant numbers of U-boats into the area of the English Channel off Normandy and so open the possibility of sinking or severely damaging significant numbers of the Allied ships involved in ‘Neptune’ (iii) and ‘Overlord’ (6/30 June 1944).
In pursuance of this objective, on 6 June a total of 36 U-boats was despatched from bases in German-occupied France (17 from Brest, 14 from St Nazaire, four from La Pallice and one from Lorient) as the ‘Landwirt’ wolfpack. On 7 June U-989 was damaged by a Vickers Wellington medium-range anti-submarine aeroplane of the RCAF’s No. 407 Squadron and a Consolidated Liberator long-range maritime reconnaissance bomber of the RAF’s No. 224 Squadron, which were both shot down by the U-boat. U-212 was damaged by two de Havilland Mosquito fighter-bombers of the RAF’s No. 248 Squadron. The damaged U-boats all had to return to base. On 8 June Kapitänleutnant Hans-Heinrich Ketels’s U-970 of the outbound Brest boats was sunk by a Short Sunderland flying boat of the RAF’s No. 228 Squadron; a Wellington of the RAF’s No. 179 Squadron damaged U-415; a Liberator of the RAF’s No. 53 Squadron damaged U-963 and U-256; a Liberator of the RAF’s No. 53 Squadron sank Oberleutnant Hans-Helmuth Bugs’s U-629 and a Liberator of the RAF’s No. 224 Squadron sank Oberleutnant Detlef von Lehsten’s U-373 and possibly Kapitänleutnant Klaus Hartmann’s U-441; and a Handley Page Halifax maritime reconnaissance bomber of the RAF’s No. 502 Squadron damaged U-413. Kapitänleutnant Günther Stark’s U-740 was lost on or after 6 June to causes unknown.
It proved wholly impossible for the Germans to introduce U-boats not fitted with Schnorchel equipment into the English Channel, so U-766 of the Brest boats, U-228, U-255, U-260, U-270, U-281, U-382, U-437, U-445, U-608, U-650, U-714, U-758, U-985 and U-993 of the St Nazaire boats, U-262 and U-333 of the La Pallice boats, and U-981 from Lorient therefore remained in the Bay of Biscay until 15 June.
Of the nine Schnorchel-fitted boats, U-212 had to return twice, but the others eight attempted to enter the Allied invasion area from the west, followed by U-767, U-1191, U-988, U-671 and U-971 coming from Norway.
On 7 and 8 June U-984, U-621 and U-953 fired respectively four, two and four torpedoes at the four destroyers of the 12th Escort Group, but all the weapons detonated prematurely or in the ships’ wakes. Early on 9 June U-764 fired four torpedoes during a destroyer action without securing a hit. Up to 11 June U-621, U-269 and U-275 attacked groups of destroyers in the western entrance to the English Channel, but without success.
Oberleutnant Ulrich Knackfuss’s U-821 was sunk in an attack by four Mosquito machines, of which one was lost, of the RAF’s No. 248 Squadron and a Liberator of the RAF’s No. 206 Squadron. On 11 June a Sunderland of the RAF’s No. 228 Squadron damaged U-333 but was itself shot down. On 12 June a Liberator of No. 224 Squadron was shot down and two days later U-270 shot down a Liberator of the RAF’s No. 53 Squadron but was itself damaged by a Wellington of No. 172 Squadron.
From 14 June the first U-boats reached the shipping routes at the same time as the arrival of Allied support groups, some of which were moved into the English Channel. On 14 June U-984 missed a hunter/killer group and on 15 June Oberleutnant Hermann Stuckmann’s U-621 sank LST-280, Oberleutnant Walter Dankleff’s U-767 sank the frigate Mourne operating with the 5th Support Group, and Oberleutnant Hanskurt von Bremen’s U-764 hit the frigate Blackwood of the 4th Support Group, which was taken in tow but later declared a total loss. On 18 June U-621 missed two US battleships with a torpedo salvo. Dankleff’s U-767 was sunk on 18 June by the destroyers Fame, Inconstant and Havelock of Commander R. A. Currie’s 14th Support Group.
Of the Schnorchel-fitted U-boats arriving in the second half of June, U-763 missed a search group with two torpedoes during the night of 22/23 June; and, after being damaged in air attacks on 20 and 26, Oberleutnant Walter Zeplien’s U-971 was sunk in the western end of the English Channel by the destroyers Eskimo and Haida after the failure of its own attack attempt. On 25 June the frigate Bickerton sank Oberleutnant Georg Uhl’s U-269. Oberleutnant Peter Grau’s U-1191 was lost to unknown causes some time after 12 June. U-984 of the same group torpedoed the frigate Goodson but missed another. Oberleutnant Klaus-Dietrich Steffens’s Schnorchel-fitted U-719 was sunk on 26 June by the destroyer Bulldog. Between 27 and 29 June Oberleutnant Erich Dobberstein’s U-988 torpedoed and damaged the corvette Pink, which was declared a total loss, and sank the 2,385-ton British Maid of Orleans and 7,058-ton British Empire Portia before itself being sunk on 29 June by a Liberator of the RAF’s No. 224 Squadron in combination with the frigates Cooke, Dornett, Duckworth and Essington of Commander R. G. Mills’s 3rd Support Group.
On 29 June U-984 attacked the EMC.17 convoy and hit the 7,240-ton Edward M. House, 7,176-ton H. G. Blasdel, 7,176-ton James A. Farrell and 7,198-ton John A. Treutlen: Edward M. House was run aground and later salved, but the other three were total losses. U-671 missed a destroyer of a search group on 30 June and, after another unsuccessful attack on a search group on 2 July, was depth-charged and damaged, and had to put in to Boulogne.
The Schnorchel-equipped U-214 and U-218 laid mines off Plymouth on 26 June and off Land’s End on 1 July.