'Dränger' was a U-boat wolfpack operation, in concert with 'Raubgraf' and 'Stürmer' (i), in the Atlantic Ocean against the HX.229 and SC.122 convoys (14/20 March 1943).

The wolfpack comprised U-86, U-221, U-333, U-336, U-373, U-406, U-440, U-441, U-590, U-608 and U-610, and for the loss of none of its own number sank three ships totalling 20,718 tons in what was the largest convoy operation of World War II.

To avoid the 'Raubgraf' wolfpack, which was shadowing the ON.170 convoy, the SC.122 and HX.229 convoys were switched 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 whale factory ship Svend Foyn and two ships that had to turn back as a result of ice damage.

The instructions radioed to the SC.122 and HX.229 convoys were intercepted and decrypted by the B-Dienst, the German naval radio interception and decryption service, on 14 March and Grossadmiral Karl Dönitz, commander-in-chief of the German navy but still in operational control of the U-boat arm, was thus able to order 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 a narrow patrol line as the 'Raubgraf' wolfpack in front of the route predicted for SC.122 on 15 March.

On the eastern side of the North Atlantic, the 'Stürmer' (i) wolfpack was formed to operate against the SC.122 convoy with the boats coming from the SC.121 convoy battle (U-190, U-229, U-305, U-338, U-439, U-523, U-526, U-527, U-530, U-618, U-641, U-642, U-665 and U-666) and, from 14 March, the newly arrived U-134, U-384, U-598 and U-631.

The 'Dränger' wolfpack was established to tackle the HX.229 convoy on the German assumption that this convoy would be routed farther to the south, and comprised boats coming from the HX.228 convoy battle (U-86, U-221, U-333, U-336, U-373, U-406, U-440, U-441, U-590, U-608 and U-610).

On the Allied side, the ONS.171 and ON.172 convoys, supported by the British Escort Group B1 and Canadian Escort Group C3 respectively, were routed to the north because of the assumed concentration of U-boats from the preceding battles against the SC.121 and HX.228 convoys.

In very heavy weather, the SC.122 convoy passed through the 'Raubgraf' wolfpack’s planned patrol line before the U-boats were able to assume position, and the HX.229 convoy skirted the German line to the south. U-91 spotted the British destroyer Witherington, detached from the western local escort force after running short of fuel but, operating 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. Of its naval support, Lieutenant Commander G. J. Luther’s British Escort Group B4 (the destroyer Volunteer and the corvettes Anemone and Pennywort), and the destroyer Mansfield of the western local escort force, were operating with the convoy, and immediately drove off U-653.

Dönitz deployed the 'Raubgraf' wolfpack of two boats, 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 erroneously assumed to be the SC.122 convoy.

The 'Raubgraf' boats established contact with the HX.229 convoy again during the afternoon of 16 March, notwithstanding a sharp detour ordered by Luther during the night 16/17 March, and attacked the lightly escorted convoy in quick succession. 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 torpedoed and damaged the 7,176-ton US James Oglethorpe which was later sunk by Kapitänleutnant Heinz Walkerling’s U-91; Korvettenkapitän Siegfried Strelow’s U-435 torpedoed the 7,196-ton US William Eustis which was later sunk by Walkerling’s U-91; and U-91 attacked simultaneously with U-435 to sink the 6,366-ton US Harry Luckenbach; U-616 missed Volunteer; Kapitänleutnant Bernhard Zurmühlen’s U-600 hit three vessels with pattern-running torpedoes which sank the 12,156-ton British whale factory ship Southern Princess and damaged the 6,135-ton US Iréné du Pont and 8,714-ton British Nariva which that were later sunk by U-91; and U-228 missed 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 escorted by Commander R. C. Boyle’s British Escort Group B5 (the destroyer Havelock, the frigate Swale, the corvettes Buttercup, Lavender, Pimpernel and Saxifrage, and the rescue ship Zamalek), plus the US destroyer Upshur coming from the ON.170 convoy after delivering the Icelandic component of the convoy. The corvette Godetia arrived from astern after rescuing the crew of the anti-submarine trawler Campobello, which had foundered in the gale. Havelock and Zamalek had HF/DF equipment, and this proved useful in allowing the escort to find and drive off the U-boats.

Only Kapitänleutnant Manfred Kinzel’s U-338 reached a firing position, and sank the 7,886-ton Dutch Alderamin, 4,071-ton Panamanian Granville and 4,898-ton British Kingsbury, and also damaged the 7,134-ton British Fort Cedar Lake which was later sunk by Oberleutnant Hans-Jürgen Haupt’s U-665.

When Dönitz learned that two convoys had been located, the remaining boats of the 'Stürmer' (i) and 'Dränger' wolfpacks were redeployed. By day on 17 March a Consolidated Liberator four-engined long-range maritime reconnaissance bomber of the RAF’s No. 86 Squadron and then another Liberator of the RAF’s No. 120 Squadron, operating from Northern Ireland, arrived over the SC.122 convoy and, together with Swale, Upshur, Godetia and Havelock, drove off all the contact-keepers. Kinzel’s U-338 did manage to sink the 4,071-ton British King Gruffydd in a submerged daylight attack.

By this time not all of the escort warships had managed to close on the HX.229 convoy, and only Volunteer, Mansfield and the newly arrived destroyer Beverley were with the convoy when at mid-day Oberleutnant Hans-Achim von Rosenberg-Gruszcynski’s U-384 and Oberleutnant Jürgen Krüger’s U-631 made almost simultaneous attacks to sink the 7,252-ton British Coracero and 5,158-ton Dutch Terkoeli respectively. In the afternoon a Liberator of No. 120 Squadron forced the contact-keeper, U-600, to submerge, and by the morning of 18 March the Germans had lost contact, providentially for the convoy as it was now escorted only by Volunteer, Beverley, Anemone and Pennywort.

In the case of SC.122, the escorts drove off most of the many 'Stürmer' (i) and 'Dränger' boats as they come up from both sides: only Kapitänleutnant Rudolf Bahr’s U-305 had 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 had no further warships to help the escort forces, especially those of HX.229, in the area. The ON.172 convoy of 17 ships supported by Lieutenant Commander R. C. Freaker’s Canadian Escort Group C3 (the destroyer Burnham, the frigate Jed and the corvettes Bittersweet, Eyebright, Mayflower and La Malbaie) was too distant and also passing through an area in which U-boat attack was expected.

The ON.173 convoy of 39 ships, supported by Lieutenant Commander R. E. Sherwood’s British Escort Group B7 (the destroyer Vidette, the frigate Tay, and the corvettes Alisma, Loosestrife, Pink and Snowflake) was routed to the north of the U-boat concentration and lack the strength to make possible any dispersion of its capability.

The southbound KMS.11 slow convoy of 62 ships supported by the Canadian Escort Group C2 (destroyers Broadway and Sherwood, frigate Lagan, Free French sloop Savorgnan de Brazza and corvettes Primrose, Snowdrop and Canadian Morden, Drumheller and Chambly), and the KMF.11 fast convoy of nine transports accompanied by two escort groups made up of the destroyers Douglas, Eggesford, Badsworth, Whaddon, Goathland and Free Polish Krakowiak, and the sloops Wren and Woodpecker, had not only to pass the transit routes of the U-boats but were also within range of German air attack, so could not contemplate any detachments.

However, the Liberator long-range aircraft of Nos 86 and 120 Squadrons were despatched from Aldergrove in Northern Ireland and Reykjavik in Iceland. The effect was dramatic: on 18 March there were 30 U-boats still operating, but the nine close to the HX.229 convoy were all forced to dive in the face of the air threat they faced from three Liberator aircraft of No. 120 Squadron. Only Oberleutnant Hans-Hartwig Trojer’s U-221, vectored into the area by U-610, was able achieve anything, sinking the 8,293-ton British Canadian Star and 7,191-ton US Walter Q. Gresham in a submerged attack.

Two and later three Liberator aircraft of No. 120 Squadron also prevented daylight attacks on the SC.122 convoy. In the evening of 18 March and night of 18/19 March the senior officer of the British Escort Group B4, Commander E. C. Day in the destroyer Highlander, reached the HX.229 convoy together with the US destroyer Babbitt, while 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, Korvettenkapitän Herbert Engel’s U-666 fired a torpedo salvo that 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 air escort drove the U-boats away from both convoys, although a straggler, 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 19 March and during the night of 19/20 March the destroyer Vimy and corvette Abelia supplemented the HX.229 convoy’s escort, and the last contact-keepers (U-631 with HX.229 and U-642 with SC.122) were driven off in the morning.

The strength of the air escort, which now included Short Sunderland four-engined flying boats of the RAF’s No. 201 Squadron and the RCAF’s No. 423 Squadron, Boeing Fortress four-engined long-range maritime patrol bombers of the RAF’s No. 220 Squadron and Consolidated PBY twin-engined flying boats of the US Navy’s VP-84 squadron, forced the U-boats to submerge. von Rosenberg-Gruszcynski’s U-384 was sunk by a Fortress of the RAF’s 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 then arrived to strengthen the HX.229 convoy’s escort.

Given the growing strength of the convoy’s surface and air escorts as it neared the UK, Dönitz decided to end the attacks on the two convoys early on 20 March after 21 ships (140,842 tons) had been sunk. The losses of the SC.121, HX.228, SC.122 and HX.229 convoys was in the order of 20% of the ships involved, and led to British fears that the convoy system, the backbone of the Allied strategy to keep the UK in the war, might have to be abandoned.

Instead, however, the British decided to form support groups, optimised for the hunter/killer rather than convoy escort role, using destroyers of Admiral Sir John Tovey’s Home Fleet: Captain J. A. McCoy’s 3^rd Support Group had Offa, Obedient, Oribi, Orwell and Onslaught, and Captain P. Todd’s 4^th Support Group had Inglefield, Icarus, Eclipse and Fury; in addition, there was Captain G. E. Short’s US Task Unit 24.4.1 with the escort carrier Bogue and the destroyers Belknap, Osmond Ingram and George E. Badger. The British also decided that the 1^st, 2^nd and 5^th Support Groups would also be established to support convoys in danger and force them through extended U-boat lines round which the convoys could not pass.