'Mosel' was a U-boat wolfpack operation in the Atlantic against the HX.239, ON.184 and SC.130 convoys (19/24 May 1943).
The wolfpack comprised U-218, U-221, U-228, U-231, U-264, U-305, U-336, U-378, U-468, U-552, U-558, U-569, U-575, U-603, U-607, U-621, U-641, U-642, U-650, U-666 and U-752, and for the loss of Oberleutnant Hans Johannsen’s U-569 and Korvettenkapitän Karl-Ernst Schroeter’s U-752 sank no ship.
The wolfpack was created, on the orders of Grossadmiral Karl Dönitz, now commander-in-chief of the German navy but still in day-to-day control of the U-boat arm via Konteradmiral Eberhard Godt, its operations chief, to attack the HX.239 convoy of 42 laden ships bound from Halifax, Nova Scotia, to the UK and supported by Commander M. J. Evans’s British Escort Group B3 (destroyers Keppel and Escapade, frigate Towy, and corvettes Orchis, Narcissus and Free French Roselys, Lobélia and Renoncule).
The convoy’s location had been discovered through the radio intercept and decryption efforts of the B-Dienst, and the British responded to the resulting U-boat concentration, discovered by 'Ultra' decrypts of the German Enigma-encrypted radio traffic, by altering the convoy’s route. This Allied change was also detected by the B-Dienst, and there was time for the 'Mosel' wolfpack to be shifted to a new interception area farther to the south.
During the evening of 21 May the ON.184 convoy of 39 ships bound from the UK to the USA, and supported by the Canadian Escort Group C1 (British frigate Itchen, destroyers St Laurent and St Croix, and corvettes Agassiz, Sackville and Woodstock) reached this new patrol line from the east. The convoy and its escort were further supported by Captain G. E. Short’s US 6th Support Group (escort carrier Bogue and destroyers Belknap, Greene, Osmond, Ingram and George E. Badger).
Grumman Avenger bombers from Bogue damaged U-231, and the destroyers Osmond, Ingram and St Laurent compelled two other boats to submerge. The ON.184 convoy was then able to pass through the resulting gap.
On 22 May U-468 beat off an Avenger with its anti-aircraft fire, and only at about 12.00 did a report about the convoy come through from Kapitänleutnant Rudolf Bahr’s U-305. The more southerly boats of the 'Mosel' wolfpack were deployed, but U-305 was bombed on three occasions by Avenger aircraft and damaged. In the afternoon two Avengers of the VC-9 squadron from Bogue sank U-569.
At the same time Kapitänleutnant Richard Becker’s U-218 heard the HX.239 convoy, and the remaining boats of the 'Mosel' and 'Donau' wolfpacks, the latter coming from the attack on the SC.130 convoy, were now deployed against this target. However, the convoy’s supporting force had been further strengthened with the arrival of Captain A. K. Scott-Moncrieff’s British 4th Support Group (escort carrier Archer and destroyers Eclipse, Fury, Matchless and Milne).
A Fairey Swordfish anti-submarine aeroplane from Archer was beaten off by U-468, which with U-218 also escaped from a destroyer attack.
U-664 and U-413 reported the convoy on 23 May but no U-boat made an attack. U-752 was hit while diving in an attack by a Swordfish of the Fleet Air Arm’s No. 819 Squadron during the first successful use of rockets in the anti-submarine role, but used its quadruple 20-mm anti-aircraft cannon mounting to hold off three other Swordfish and one Grumman Wildcat fighter of the FAA’s No. 869 Squadron from Archer. This boat was then scuttled by its crew when approached by the destroyers Keppel and Escapade.
In the end, both convoys passed the U-boat concentration without loss.