Convoy SL 140/MKS 31

Convoys SL 140/MKS 31 were two Allied convoys which ran during the Battle of the Atlantic in World War II. SL 140 was part of the OS/SL series, between Britain and the South Atlantic, MKS 31 was one of the KMS/MKS series between Britain and the Mediterranean.

They were sailing together on the Gibraltar homeward route, having made a rendezvous off Gibraltar in late November 1943.

They were the subject of a U-boat attack, as part of the German Navy’s (Kriegsmarine (KM)’s) renewed Autumn offensive.

Background
Following the renewal of the U-boat offensive in the Atlantic, convoys on the UK/Gibraltar routes had again come under attack, leading to clashes over Convoy SL 138/MKS 28 and Convoy SL 139/MKS 30. German U-boat Control (BdU) had subsequently re-organized its patrol lines off the coast of Portugal, so as to find and attack the next convoys on this route. As before, the Admiralty were running these in tandem, bringing together the South Atlantic and the Mediterranean routes at Gibraltar.

Protagonists
SL 140 left Freetown on 12 November 1943, arriving off Gibraltar on 24 November. It comprised 35 ships and was escorted by an Escort Group of four warships. MKS 31 sailed from Port Said on 13 November, similarly arriving off Gibraltar on 24 November to meet SL 140.

The combined body of 65 ships then sailed for Britain. It was escorted by B-1 Escort Group, of seven warships, led by HMS Hurricane, (Commander EC Bayldon).

Opposing this force was patrol group Weddigen, consisting of thirteen U-boats, comprising boats already on station from the disbanded Schill group, with reinforcements from the North Atlantic and from bases in occupied France.

Action
The two convoys made their rendezvous at noon on 24 November 1943, a total of 65 ships initially escorted by the B-1 Escort Group, of seven warships. The combined convoys were sighted by German aircraft in the late afternoon of 26 November, west of Cape St Vincent, but were able to evade the shadow with a radical course change during the night. The convoy was reinforced by the destroyer Watchman, also on the 26th.

On 27 November the convoys were found again by aircraft, which brought in U-262. She commenced shadowing until other Weddigen boats could be homed-in. Also during the 27th the convoy was joined by 4 EG, a Support Group of five frigates led by HMS Bentinck (Cdr EH Chavasse). By evening the U-boats had gathered and started their assault. Franke, in U-262 was able to penetrate the escort screen into the convoy itself, he attacked the ships there from close range, a tactic used by aces Kretschmer and Schepke two to three years earlier. However his boldness was not rewarded by any success; he fired at, and claimed hits on, three ships, but no hits were confirmed. The three other boats that penetrated the screen, U-764, U-107, and U-238, also failed to make any hits. During the night the convoy was again reinforced by the arrival of 2 EG, a Support Group led by Captain F.J. "Johnnie" Walker, Britain's most successful anti-submarine warfare commander, in HMS Starling. This brought the total number of escorts for the convoy to seventeen warships. On 28 November U-238 picked up two allied airmen whose aircraft had crashed. U-238’s skipper, Horst Hepp, radioed a long account of his interrogation of them, which was intercepted and tracked by HF/DF (radio direction finding). Hepp was meanwhile ordered to meet U-764, which was returning to base, in order to transfer the prisoners. Allied forces were sent to intercept the two U-boats, with a view to rescuing the airmen, and prevent the two boats from getting away. Both U-764 and U-238 were attacked the following day by aircraft from the escort carrier USS Bogue; both were damaged, but both were able to escape.

Also on 28 November, 2 EG located U-842 and subjected her to a prolonged attack, but she also was able to escape. But by now outnumbered by the convoy escort, Weddigen had little chance of achieving any success; BdU ordered a halt to the attack.

SL 140 and MKS 31 continued their passage without further incident, arriving at Liverpool on 26 November 1943.

Aftermath
Despite the energy of the attack on SL 140/MKS 31 no ships were sunk, nor U-boats destroyed. The escort had successfully beaten off every attack, although the failure to destroy any of the attacking U-boats, despite the presence of two Support Groups, was disappointing to the Allies. Franke, of U-262 received the Knight's Cross of the Iron Cross for this and previous actions on this patrol; significantly the citation commented on the toughness and tenacity shown as the reason for the award, rather than for any major success, as in previous years. BdU recognized that in this phase of the U-boat offensive "the prospects of sinkings were slight"