This was a German operation to run U-boats individually from the Atlantic into the Mediterranean through the Strait of Gibraltar (5/18 November 1941).
The boats involved were U-81, U-205, U-433 and U-565, all of which departed France for the Mediterranean on 5 November, passed through the Strait of Gibraltar between 11 and 16 November, and initially patrolled in the area to the east of Gibraltar.
in November Adolf Hitler, in the mistaken belief that the role in which the U-boat arm could make its greatest contribution to the Axis war effort was changing from the decimation of British convoys in the Atlantic Ocean, a primary theatre, to the protection of Axis convoys crossing the Mediterranean Sea between Italy and North Africa, at best a secondary theatre, ordered Vizeadmiral Karl Dönitz, the commander of the U-boat arm, to start a process of transferring boats eastward through the Strait of Gibraltar. The movement of an initial six boats was ordered, and shortly after this another four boats.
The value of this change seemed to be attested by early successes. Early on 13 November and in the afternoon of the same day, Kapitänleutnant Franz-Georg Reschke’s U-205 and Kapitänleutnant Friedrich Guggenberger’s U-81 launched torpedoes at ships of Vice Admiral Sir James Somerville’s Gibraltar-based Force 'H' returning from their part in 'Perpetual' and whose presence had been reported on 12 November by Italian reconnaissance aircraft. One of U-81's four torpedoes hit Ark Royal, and the carrier sank while in tow during the following day.
On 16 November Oberleutnant Hans Ey’s U-433 tried to attack a convoy setting out to the east from Gibraltar, but was then sunk by the corvette Marigold. On 18 November the surviving three boats moved to the eastern Mediterranean.
On 22 November Hitler ordered that the transfer of the entire force of operational U-boats from the Atlantic to the Mediterranean. Further evidence of the apparent success of the change was provided by the sinkings of the battleship Barham by Oberleutnant Hans-Diedrich Freiherr von Tiesenhausen’s U-331 on 25 November then of the light cruiser Galatea by Korvettenkapitän Ottokar Arnold Paulssen’s U-557 on 15 December.