Convoy SL 138

Convoy SL 138/MKS 28
Part of World War II
Date 27–31 October 1943 Location Mid Atlantic Result British operational victory
Belligerents
United Kingdom	Germany
Commanders and leaders
Convoy Comm AM Hekking Escort:Lt Cdr. F Ardern	Admiral Karl Dönitz
Strength
60 ships 14 escorts	8 U-boats
Casualties and losses
1 ship sunk	1 U-boat destroyed

Convoys SL 138/MKS 28 were two Allied convoys which ran during the Battle of the Atlantic in World War II. SL 138 was one of the SL convoys from the South Atlantic to Britain, and MKS 28 one of the MKS convoys between Britain and the Mediterranean. They were sailing together on the Gibraltar homeward route, having made a rendezvous off Gibraltar in order to cross the Bay of Biscay with the maximum possible escort. They were the subject of a major U-boat attack in October 1943, the first battle in the Kriegsmarine's renewed Autumn offensive.

Following the defeats of May 1943, and the devastating losses incurred by the U- boat Arm (U-Bootwaffe) (UBW) Adm Dönitz had withdrawn from attacks on the North Atlantic route while awaiting tactical and technical improvements. By September 1943 these were ready, and U-boat Control (Befehlshaber der Unterseeboote)(BdU) had re-opened the offensive in the North Atlantic. After several disastrous convoy battles, which had cost the U-boat Arm 32 U-boats destroyed for little gain (three escorts and two merchant ships sunk, and several others damaged) BdU had again withdrawn from the North Atlantic battleground. As had happened after Black May he again switched the focus of the campaign to the Mid-Atlantic and South Atlantic routes, reasoning these would be softer targets. To this end he established the "wolfpack" Schill off the coast of Portugal, to intercept convoys sailing to and from Gibraltar, Mediterranean and South Atlantic.

For the Allies, the success of Operation Torch and the re-opening of the Mediterranean to Allied traffic had led to the Allied convoy system in this area being re-organized. The previous OG/HG series to Gibraltar had been discontinued, to be replaced by the MKS/KMS series of ships to and from the Mediterranean. The OS/SL series to Freetown and the South Atlantic continued, but now the two routes were combined from Gibraltar; SL convoys from Freetown now making a rendezvous with MKS convoys from North African ports for the final leg of the journey to Britain. Similarly the OS and KMS convoys travelled together across the Bay of Biscay, before parting off Gibraltar.

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