This was a U-boat wolfpack operation in the North Atlantic against the SC.129 convoy (10/14 May 1943).
The wolfpack comprised U-103, U-107, U-186, U-223, U-359, U-377, U-383, U-402, U-448, U-454, U-466, U-504 and U-621, and for the loss of Korvettenkapitän Siegfried Hesemann’s U-186 sank two ships (7,627 tons) on 11 May. These were the 4,545-ton British Antigone and 3,082-ton Greek Grado, which both fell victim to Korvettenkapitän Siegfried von Forstner’s U-402.
The SC.129 convoy was an eastbound North Atlantic convoy which ran during the Battle of the Atlantic, and was one of the several convoy battles which took place during the crisis month of May 1943.
The convoy had 25 ships, plus local contingents, and departed New York on 2 May 1943 with Captain R. D. Binks as commodore in the 4,916-ton British Baltrover and bound for Liverpool with cargoes of war materials.
The Mid-Ocean Escort Force’s British Escort Group B2 joined the convoy from St John’s, Newfoundland and Labrador on 6 May. Under Commander D. G. F. W. MacIntyre in the destroyer Hesperus, this group also comprised the destroyers Vanessa and Whitehall, and the corvettes Clematis, Gentian, Heather and Sweetbriar. They were joined for the voyage by the armed trawlers Lady Madeleine and Sapper, the rescue ship Melrose Abbey and the 11,191-ton Panamanian oiler Orville Harden.
Arrayed against them in the North Atlantic were the 'Rhein' (iv), 'Elbe II' and 'Drossel' wolfpacks, although in the event only the 'Elbe II' wolfpack, re-configured and eventually comprising 13 U-boats, engaged SC.129.
The wolfpack made first contact with the convoy on 11 May in the form of a sighting report by U-504, which vectored the wolfpack’s other boats toward the convoy’s location as it started to shadow the convoy. Alerted by the German radio activity, the Admiralty ordered Captain E. M. C. Abel-Smith’s British 5th Support Group, comprising escort carrier Biter and destroyers Obdurate, Opportune and Pathfinder, to join the convoy’s defence. the 5th Support Group was currently supporting the HX.237 convoy, which was under attack by boats of the 'Rhein' (iv) and 'Drossel' wolfpacks, but came within range of support by the long-range aircraft of RAF Coastal Command, and it was this which decided the Admiralty that the SC.129 convoy was in greater need of the reinforcement which could be provided by the 5th Support Group.
The report by U-504 had brought up about 12 U-boats, and on the evening of 11 May U-402 slipped past the escorts and torpedoed the freighters Antigone and Grado. Both merchant ships sank, Antigone with the loss of three of her crew. In his own words, MacIntyre was 'furious' that ships under his group’s protection had been sunk: during the preceding nine months Escort Group B2 had escorted large numbers of convoys without loss. MacIntyre organised a vigorous hunt for the U-boat, which was located by Gentian, depth-charged and so badly damaged she was forced to abandon its patrol and return to base. Later that night Hesperus gained contact with U-223 and attacked: the depth-charge and subsequent ramming damaged U-223 so badly damaged that this boat too was forced to retire.
On returning to the convoy Hesperus found another U-boat in the early hours of 12 May. This was U-186, which was tracking the convoy. Hesperus closed quickly, and as the U-boat crash-dived, attacked it with depth charges. This time the boat was destroyed, with all hands lost.
During 12 May the assembled U-boats made more than 12 separate attempts to penetrate the escort screen, but an aggressive defence by the warships, despite the fact that they were low on fuel and ammunition, prevented any losses.
On 13 May the convoy was joined by the 5th Support Group with Biter and her destroyers. Hesperus and her group were now able to refuel and re-arm, and Biter was able to mount continuous air cover over the convoy and its environs. At this point Grossadmiral Karl Dönitz, the commander-in-chief of the German navy since 30 January 1943, and Konteradmiral Eberhard Godt, the operational commander of the U-boat arm, appreciated that there was nothing more to be achieved, and called off the attack of the 'Elbe II' wolfpack’s boats, though they continued to shadow the convoy until 17 May, when the 'Elbe II' wolfpack was disbanded.
The SC.129 convoy reached Liverpool without further incident on 22 May.
The passage of the SC.129 convoy was a significant success for the Allies as, despite the loss of two ships, 23 ships arrived safely. Added to this, an attack by a wolfpack of 12 U-boats had been beaten off, one U-boat had been destroyed, and two more so badly damaged they had to return to base. The convoy was another in a series of set-backs suffered by the U-boat arm collectively known to the Germans as schwarz Mai (black May).