This was a U-boat wolfpack operation in the Atlantic (7/13 April 1943).
The wolfpack comprised U-71, U-84, U-108, U-188, U-257, U-381, U-404, U-413, U-438, U-571, U-613, U-615, U-618 and U-662, and for the loss of none of its own number sank four ships (14,166 tons), including the British destroyer Belvedere, in attacks on the HX.232, ON.176 and ONS.2 convoys.
The 'Adler' (iii) wolfpack was brought into existence on 7 April in the North Atlantic in the area to the south of Greenland, and on the same day the expected SC.125 convoy, supported by Commander R. Heathcote’s British Escort Group B6 (destroyers Fame and Viscount, and corvettes Vervain, Kingcup and Free Norwegian Potentilla, Eglantine, Rose and Acanthus), passed to the west of the German patrol line. Kapitänleutnant Heinz Rahe’s U-257 spotted the escorting warships, but Kapitänleutnant Siegfried Lüdden’s U-188, U-257 and Kapitänleutnant Horst Uphoff’s U-84 did not reach the position, and a patrol line established farther to the north on 8 April was unsuccessful.
The wolfpack was accordingly moved farther to the south so that it could operate against the expected HX.232 convoy supported by the British Escort Group B3. During the afternoon of 10 April Korvettenkapitän Otto von Bülow’s U-404 reported the ON.176 convoy of 46 ships supported by the British Escort Group B4 (destroyers Highlander, Beverley and Vimy, and corvettes Pennywort, Asphodel, Anemone, Abelia and Clover). Of the 'Adler' (iii) wolfpack’s boats, U-188 sank Beverley in a night attack on the convoy.
The shadowing boats, Kapitänleutnant Helmut Mählmann’s U-571 and Uphoff’s U-84, found the ONS.2 convoy of 37 ships supported by Lieutenant Commander G. H. Steven’s Canadian Escort Group C1 (destroyers St Laurent and St Croix, corvettes Battleford, Kenogami, Napanee and Shediac and, in addition during their return from 'Torch' duty, the corvettes Camrose, Kitchener, Moosejaw and Ville de Quebec). In the attack on the ONS.2 convoy, Mählmann’s U-571 sank the 3,835-ton Norwegian Ingerfire. On 11 April Kapitänleutnant Ralph Kapitzky’s U-615 and Korvettenkapitän Helmut Köppe’s U-613 each sank a single straggler (7,177-ton US Edward B. Dudley and 1,914-ton British Lancastrian Prince respectively). U-71, U-662, U-404 and once again U-71 maintained contact with the convoy for a short time, but all the boats were then driven off by the strong air and sea escort.
Only U-404 managed to deliver an attack on ON.176 during the night of 11/12 April, but without success. U-84, U-662, U-404, U-613 and U-571 had to break off after suffering varying degrees of damage, and 'Adler' (iii) was abandoned on 12 April.
Two other convoys (ON.177 accompanied by the Canadian Escort Group C4 with the destroyers Churchill and Canadian Restigouche, and the Canadian corvettes Amherst, Brandon and Collingwood, together with the Free Norwegian destroyer St Albans on transfer, and ONS.3 supported by the 40th Escort Group with the sloops Aberdeen, Hastings and Lulworth, and the frigates Moyola and Waveney) passed clear of the wolfpacks after being rerouted in the light of 'Ultra' decrypts.