This was a U-boat wolfpack operation, in tandem with ‘Knappen’, in the Atlantic against the HX.226 and ON.166 convoys (11/26 February 1943).
The wolfpack comprised U-92, U-225, U-332, U-377, U-454, U-468, U-529, U-603, U-621, U-623, U-628, U-653 and U-753, and for the loss of Oberleutnant Hermann Schröder’s U-623 sank five ships (33,376 tons) and damaged another four ships (28,662 tons) in attacks on the ON.166 convoy.
The ‘Ritter’ wolfpack was created specifically to attack the HX.226 convoy of 63 ships which had departed Liverpool for the eastern seaboard of the USA on 11 February with the support of Lieutenant Commander T. Taylor’s Canadian Escort Group C3 (British destroyer Burnham, British frigate Jed, and corvettes Bittersweet, Eyebright and La Malbaie). The existence and progress of the convoy were known to the Germans through radio intercepts and decrypts by the B-Dienst.
On 15/16 February the SC.119 convoy, supported by Commander E. C. Bayldon’s British Escort Group B1 (destroyers Hurricane, Rockingham and Watchman, frigate Kale, and corvettes Dahlia, Meadowsweet, Monkshood and Wallflower) was re-routed somewhat farther to the north than had been planned but passed the ‘Ritter’ wolfpack’s patrol line without being spotted. An escorting Consolidated Liberator long-range patrol bomber of the RAF’s No. 120 Squadron sank Oberleutnant Wolfgang Leimkühler’s U-225.
On the basis of ‘Ultra’ intelligence of U-boat movements and concentrations, the HX.226 convoy was also ordered to effect a wide detour to the north and on 18 February also passed the ‘Ritter’ wolfpack’s patrol line without being spotted. On 17 February, again on the basis of ‘Ultra’ intelligence, the ON.166 and following ONS.167 convoys were re-routed to the south of the ‘Ritter’ wolfpack while this and the new ‘Neptun’ wolfpack were establishing a long patrol line to intercept ON.166 along its original route as advised by the B-Dienst.
On 18/19 February, however, the decryption of reports from escorting aircraft revealed to the Germans the ON.166 convoy’s south-westerly route, and the outbound U-91, U-92, U-600 and U-604 were used to create the ‘Knappen’ wolfpack to the south-east of the ‘Ritter’ wolfpack.
Just before 12.00 on 20 February, U-604 sighted and reported the ON.166 convoy, currently comprising 40 ships and nine stragglers supported by Commander Paul R. Heineman’s US Escort Group A3 (US Coast Guard cutters Spencer and Campbell, Canadian corvettes Chilliwack, Dauphin, Rosthern and Trillium, and British corvette Dianthus). During the night of 20/21 February U-604 was located by Spencer’s radar and depth-charged before the arrival of the pack’s other boats. During the morning of 21 February U-753 found the 5,964-ton Norwegian Stigstad, a straggler from the ON.166 convoy, and this was later sunk by Oberleutnant Hans-Joachim Bertelsmann’s U-603 and Oberleutnant Eberhard Hüttemann’s U-332. U-623 was sunk by a Liberator of No. 120 Squadron.
In the afternoon of the same day U-91 was bombed by a flying boat which also drove away U-332, U-454 and U-753 in co-operation with Campbell, Dauphin and Dianthus.
During the night of 21/22 February Kapitänleutnant Adolf Oelrich’s U-92 made two approaches to the convoy and torpedoed the 9,990-ton British Empire Trader and 9,348-ton Norwegian N. T. Nielsen-Alonso: the former was detached with Dauphin but later had to be sunk by this corvette, and the latter was sunk by the Free Polish destroyer Burza, which had joined the escort from the ONS.167 convoy after U-92 and U-753 had tried to finish the Norwegian vessel.
At this time Spencer or a Liberator of No. 120 Squadron sank Kapitänleutnant Georg-Werner Fraatz’s U-529, whose loss became known to the Germans only in March.
During the short daylight hours of 22 February, U-606, U-603 and U-628 kept contact in turn, bringing up U-92, U-358, U-223, U-186 and U-753 by the fall of night, though most of these boats were soon driven off. U-753, which was depth-charged by Rosthern and Trillium, and Oberleutnant Hans-Heinrich Döhler’s U-606 attacked the convoy almost simultaneously. The latter boat torpedoed the 5,687-ton US Chattanooga City, 6,615-ton British Empire Redshank and 4,959-ton US Expositor: the first two sank, and the third went down only after being torpedoed once more by Kapitänleutnant Karl-Franz Heine’s U-303. Immediately after its own attack run, Döhler’s U-606 was depth-charged by Chilliwack and Burza, and shortly after this collided with Campbell and sank. Campbell became unmanoeuvrable after water started to flood her engine room, and was then taken in tow by Burza. During the night Kapitänleutnant Horst Höltring’s U-604 sank the 1,683-ton rescue ship Stockport.
During the morning of 23 February Oberleutnant Heinrich Hasenschar’s U-628 and Kapitänleutnant Siegfried Hesemann’s U-186 made almost simultaneous attacks: the former torpedoed the 6,907-ton Panamanian Winkler and 6,409-ton Norwegian Glittre, which were later sunk by Oberleutnant Karl-Jürg Wächter’s U-223 and Bertelsmann’s U-603, and the latter sank the 6,207-ton British Eulima and 5,401-ton US Hastings. These attacks were facilitated by the fact that the convoy was at this time escorted only by Spencer, Rosthern, Chilliwack and Dianthus, with the latter somewhat astern on the convoy proper to support the disabled ships.
On 23 February U-628 and U-707 maintained contact with the convoy, and by the evening had brought up U-92, U-358, U-468, U-600, U-621 and U-653. At the time escorted by only three warships, the convoy made a sharp alteration of course in the dark and managed to lose the U-boats. Even so, the straggling 7,176-ton US Jonathan Sturges was sunk by Oberleutnant Günter Gretschel’s U-707 and the 9,382-ton Dutch Madoera was damaged by U-653. In the morning Kapitänleutnant Bernhard Zurmühlen’s U-600 torpedoed the 4,391-ton Norwegian Ingria from the convoy, which was now being escorted by Spencer, Chilliwack, Rosthern and Trillium: Ingria was later sunk by Hasenschar’s U-628. On 24 February U-628 and U-603 maintained contact with the convoy and brought up U-600, U-604 and U-621, of which U-604 was depth-charged and damaged.
The arrival of air escort from Newfoundland now drove off the U-boats, though U-621 missed Spencer during the evening. The escort was then strengthened by the arrival of the British destroyers Montgomery and Witherington. Toward morning on 25 February U-628, U-92 and U-600 attacked almost simultaneously: the first sank the 7,264-ton British Manchester Merchant, and the other two missed Spencer. On 25 February U-468 maintained contact, but the visibility was now deteriorating and U-600 and U-621 managed to locate the convoy, albeit only briefly.
The U-boats lost contact in the evening, and the U-boat arm terminated the operation in the morning of 26 February.