'Raubgraf' was a U-boat wolfpack operation, in tandem with 'Dränger' and 'Stürmer' (i), in the Atlantic against the ONS.169, ON.170 SC.122 and HX.229 convoys (7/20 March 1943).
The wolfpack comprised U-84, U-89, U-91, U-435, U-468, U-600, U-603, U-615, U-621, U-638, U-653, U-664 and U-758, and for the loss only of Oberleutnant Hans-Achim von Rosenburg-Gruszcinski’s U-384 sank 22 ships (146,596 tons) in attacks on the SC.122 and HX.229 convoys. Five of the U-boats left the pack on 14 March after an unsuccessful attack on the ON.170 convoy.
The 'Raubgraf' wolfpack was created on the basis of the boats remaining from the 'Wildfang' and 'Burggraf' wolfpacks to establish a new patrol line to the north-east of Newfoundland for the interception of the HX.228 convoy, but the decryption of German Enigma-coded signals provided the 'Ultra' intelligence which allowed the convoy to be diverted to the south on 8 March, a fact revealed to the Germans one day later as the B-Dienst decrypted the relevant radio signal.
At this time the ON.168 convoy, supported by Commander R. C. Boyle’s British Escort Group B5 (destroyers Havelock and Volunteer, frigate Swale, and corvettes Buttercup, Godetia, Lavender, Pimpernel and Saxifrage), and the ONS.169 convoy supported by the Commander E. C. L. Day’s British Escort Group B4 (destroyers Highlander and Beverley, and corvettes Abelia, Anemone and Pennywort, with Canadian corvette Sherbrooke attached) had many stragglers after running into severe weather, which had also delayed the two convoys. Moreover, the escorts were starting to run short of fuel as the combination of high winds and tall seas made refuelling at sea impossible.
On 7 March the 6,537-ton British Empire Light, straggling from the ON.168 convoy, was torpedoed by Kapitänleutnant Hinrich-Oscar Bernbeck’s U-638, and the 7,176-ton US Thomas Hooker of the ONS.169 convoy signalled that she was breaking up, although the corvette Pimpernel managed to take off this Liberty ship’s crew. These signals were intercepted and decrypted by the B-Dienst, and the wrecks were sunk on 12 March by Oberleutnant Klemens Schamong’s U-468 and Kapitänleutnant Gerhard Feiler’s U-653 respectively. On 11 March Oberleutnant Max Kruschka’s U-621 sank the 3,355-ton British Baron Kinnaird, a straggler from the ONS.169 convoy.
On 9 March the 'Raubgraf' wolfpack was relocated to a position farther to the north for the interception of the ON.170 convoy which, according to the B-Dienst, was expected on 10 March. When, on 11 March, the B-Dienst decrypted a signal from the delayed ON.169 convoy, which in fact had already passed the 'Raubgraf' wolfpack, the boats were redeployed farther to the west.
On 11/12 March, the B-Dienst decrypted several signals to the HX.229A convoy, supported by the British 4th Escort Group (sloops Aberdeen, Hastings, Landguard and Lulworth, and frigates Moyola and Waveney) to steam a route farther to the north, close to Newfoundland. The 'Raubgraf' wolfpack was accordingly instructed to attack this convoy. However, on 13 March the ON.170 convoy, escorted by Commander D. G. F. W. MacIntyre’s British Escort Group B2 (frigate Whimbrel, destroyers Vanessa and Whitehall, and corvettes Gentian, Heather and Sweetbriar), was not able to comply with the re-routing order because of the escorts' fuel problems, and thus continued on its original course. This caused it to run straight into the 'Raubgraf' wolfpack, and the convoy’s location was signalled by U-603. However, by use of Whimbrel's HF/DF equipment, Maclntyre was able to frustrate the attack efforts of U-435, U-468, U-600, U-603 and U-653.
In order to avoid the 'Raubgraf' wolfpack, now shadowing the ON.170 convoy, the SC.122 and HX.229 convoys were transferred from the northern to the southern transatlantic route on 13 March, and the HX.229A convoy was routed still farther to the north-north-west, close to Newfoundland and Greenland, where it met icebergs, and lost the 14,795-ton British whale factory ship Svend Foyn, which sank two days after colliding with an iceberg, while two other ships had to turn back as a result of ice damage.
The radio signals to the SC.122 and HX.229 convoys were decrypted by the B-Dienst on 14 March, and on the following day Grossadmiral Karl Dönitz, commander-in-chief of the German navy but still exercising day-to-day control of the U-boat arm via Konteradmiral Eberhard Godt, the service’s operations chief, ordered the concentration of U-84, U-91, U-435, U-600, U-603, U-615, U-664 and U-758 from the ON.170 convoy into the 'Raubgraf' wolfpack’s narrow patrol line on the expected route of the SC.122 convoy.
On the eastern side of the Atlantic, the 'Stürmer' (i) wolfpack was formed to operate against the SC.122 convoy, and the 'Dränger' wolfpack was also formed to operate against the HX.229 convoy, the Germans assuming that this convoy would continue along a course farther to the south. On the Allied side, the ONS.171 and ON.162 convoys, supported by the British Escort Group B1 and Canadian Escort Group C3 respectively, were routed farther to the north on the assumption that there would be U-boat concentrations based on those involved in the attacks on the SC.121 and HX.228 convoys.
In stormy conditions, the SC.122 convoy passed the 'Raubgraf' wolfpack’s patrol line before the boats had been able to assume their planned positions, and the HX.229 convoy evaded it to the south. U-91 sighted the western local escort force’s British destroyer Witherington, which had been detached as she was short of fuel, but in company with U-84, U-664 and U-758 was unable to locate the convoy.
During the morning of 16 March the homebound U-653 spotted the HX.229 convoy of 38 ships, supported by Lieutenant Commander G. J. Luther’s British Escort Group B4. Only the destroyer Volunteer and corvettes Anemone and Pennywort, together with the Western Local Escort Force’s British destroyer Mansfield, were protecting the convoy, and immediately drove off U-653. Dönitz deployed the 'Raubgraf' wolfpack, U-228 and U-616 which had just replenished from U-463, and the 11 most southerly boats of the 'Stürmer' (i) wolfpack against the convoy, which was wrongly believed by the Germans to be the SC.122 convoy.
The boats of the 'Raubgraf' wolfpack re-established contact with the HX.229 convoy during the afternoon of 16 March despite the convoy’s sharp change of course during the night of 16/17 March, and quickly moved to attack this important but poorly protected target. After Mansfield had driven off U-600 and U-615, Oberleutnant Hans-Joachim Bertelsmann’s U-603 sank the 5,214-ton Norwegian Elin K.; Kapitänleutnant Helmut Manseck’s U-758 sank the 6,813-ton Dutch Zaanland and damaged the 7,176-ton US James Oglethorpe, which was later sunk by Kapitänleutnant Heinz Walkerling’s U-91; U-435 damaged the 7,196-ton US William Eustis, which was later sunk by Walkerling’s U-91; and U-91 itself, attacking in concert with U-435, sank the 6,366-ton US Harry Luckenbach. U-616 missed Volunteer; Kapitänleutnant Bernhard Zurmühlen’s U-600 hit three vessels with a salvo of pattern-running torpedoes, sinking the 12,156-ton British whale factory ship Southern Princess, 6,125-ton US Iréné du Pont and 8,714-ton British Nariva later being finished by Walkerling’s U-91; and U-228 missed the returning Mansfield.
During the night of 16/17 March the 'Stürmer' (i) boats, arriving from the north, established contact with the SC.122 convoy of 51 ships supported by Boyle’s British Escort Group B5 (destroyer Havelock, frigate Swale, corvettes Buttercup, Lavender, Pimpernel and Saxifrage, and rescue ship Zamalek, as well as the US destroyer Upshur coming from the ON.170 convoy after delivering the convoy’s Iceland-bound component). The British corvette Godetia also arrived from astern having rescued the crew of the anti-submarine trawler Campobello, which had foundered. Havelock and Zamalek carried HF/DF equipment, and with their help the escort was now able to drive off the U-boats. Only Kapitänleutnant Manfred Kinzel’s U-338 was in a position to attack, and sank the 7,886-ton Dutch Alderamin, 4,898-ton British Kingsbury and 5,072-ton British King Gruffydd as well as damaging 7,134-ton British Fort Cedar Lake, which was sunk later by Oberleutnant Hans-Jürgen Haupt’s U-665.
When Dönitz learned that it was in fact a pair of convoys which had been located, the remaining boats of the 'Stürmer' (i) and 'Dränger' wolfpacks were redeployed to assist.
By day on 17 March a Consolidated Liberator long-range patrol bomber of the RAF’s No. 86 Squadron and then another Liberator of the RAF’s No. 120 Squadron arrived from Northern Ireland to provide air cover for the SC.122 convoy and, together with Swale, Upshur, Godetia and Havelock, managed to drive off all the contact-keepers. U-338, however, managed to sink one more ship, the 4,071-ton Panamanian Granville, in a submerged daylight attack. Meanwhile, not all of the HX.229 convoy’s escorts had been able to close up, and the convoy was therefore protected by only Volunteer, Mansfield and the newly arrived destroyer Beverley when at about 12.00, von Rosenberg-Gruszcynski’s U-384 and Oberleutnant Jürgen Krüger’s U-631 delivered almost simultaneous attacks to sink the 7,252-ton British Coracero and 5,158-ton Dutch Terkoelei respectively. In the afternoon a Liberator of No. 120 Squadron forced the contact-keeping U-600 to dive, and by the morning of 18 March the Germans had lost contact. This was especially fortunate for the convoy, which was now escorted only by Volunteer, Beverley, Anemone and Pennywort.
In the case of the SC.122 convoy, the escorts drove off most of the 'Stürmer' (i) and 'Dränger' wolfpacks' boats as they come up from each side of the convoy. Only Kapitänleutnant Rudolf Bahr’s U-305 enjoyed any success, sinking the 8,789-ton British Port Auckland and 4,256-ton British Zouave after the fall of night on 17 March.
The Admiralty could provide no more warships to bolster the escorts, especially that of the HX.229 convoy. The ON.172 convoy of 17 ships, supported by the Canadian Escort Group C3 (British destroyer Burnham, British frigate Jed, and Canadian corvettes Bittersweet, Eyebright, La Malbaie and Mayflower), was too distant and also in an area where U-boat attack was expected. The ON.173 convoy of 39 ships, supported by Lieutenant Commander R. C. Sherwood’s British Escort Group B7 (frigate Tay, destroyer Vidette, and corvettes Alisma, Loosestrife, Pink and Snowflake) was re-routed to the north of the U-boat concentration and was in any event too weak to risk the detachment of any warships. The KMS.11 convoy, southbound to Gibraltar with 62 ships supported by the Canadian Escort Group C2 (British destroyers Broadway and Sherwood, British frigate Lagan, British corvettes Primrose and Snowdrop, Canadian corvettes Morden, Drumheller and Chambly, and Free French sloop Savorgnan de Brazza) and the KMF.11 fast convoy of nine transports supported by two escort groups (sloops Wren and Woodpecker, destroyers Douglas, Eggesford, Badsworth, Whaddon, Goathland and Free Polish Krakowiak) had to cross the U-boats' out- and in-bound transit routes and also lay within range of German warplanes operating from bases in occupied France, so no detachments were possible.
However, the Liberator long-range aircraft of Nos 86 and 120 Squadrons could be despatched from Northern Ireland and Iceland. On 18 March, 30 U-boats were still operational in the convoys' areas, and nine of these approached the HX.229 convoy before being forced to submerge by the air escort, by two Liberator aircraft of No. 120 Squadron and, in the evening, by another Liberator of the same unit. Only Oberleutnant Hans-Hartwig Trojer’s U-221, led by U-610, was able to attack, sinking the 8,293-ton British Canadian Star and 7,191-ton US Walter Q. Gresham in a submerged attack. An initial two, and later three, Liberator aircraft of No. 120 Squadron prevented any daylight attack on the SC.122 convoy.
During the evening of 18 March and in the course of the night of 18/19 March, the British destroyer Highlander and US destroyer Babbitt of Day’s British Escort Group B4 reached the HX.229 convoy, and the US Coast Guard cutter Ingham reached the SC.122 convoy.
During the night of 18/19 March the escorts managed to drive off several U-boats, but in an attack on the HX.229 convoy U-441 and U-608 fired torpedo salvoes which missed Highlander. In an attack on the SC.122 convoy, Oberleutnant Herbert Engel’s U-666 fired a salvo which missed, but then hit the 5,234-ton Greek Carras, which was later sunk by Oberleutnant Werner Schwaff’s U-333. During the morning of 19 March the strong British air escort drove the U-boats from both convoys, although the 5,848-ton US Mathew Luckenbach was sunk by Kapitänleutnant Herbert Uhlig’s U-527 and Kapitänleutnant Werner Pietzsch’s U-523. In the afternoon of the same day and during the night of 19/20 March the corvette Abelia and the destroyer Vimy joined the escort of the HX.229 convoy, and the last contact-keepers (U-631 and U-642 with the HX.229 and SC.122 convoys) were driven off in the morning.
The air escort, which now included the Short Sunderland flying boats of the RAF’s No. 201 Squadron and RCAF’s No. 423 Squadron, Boeing Fortress long-range patrol bombers of the RAF’s No. 220 Squadron, and Consolidated Catalina flying boats of the US VP-84 squadron forced the boats to submerge: von Rosenburg-Gruszcinski’s U-384 was sunk by a Fortress of No. 206 Squadron, U-666 was damaged by a Fortress of No. 220 Squadron, and U-631 was attacked by a Sunderland of No. 201 Squadron. The Canadian corvette Sherbrooke joined the HX.229 convoy’s escort, and it was soon after this that Dönitz early on 20 March ordered that the operation be terminated.