Two Condor long-range reconnaissance aircraft were shot down by British Martlet fighters from the escort carrier HMS Audacity, which was sunk later on the voyage, along with a destroyer and two merchant ships.

Before this the U-boat Arm (U-bootwaffe) had only enough boats operational to form one patrol line at a time and their focus was on the North Atlantic convoy route.

[2] For the Allies the introduction of specialist escort groups had created the conditions for better of convoy protection tactics, giving a measure of success in countering the wolf pack threat.

It was recognised that air cover was needed to counter shadowing aircraft, to seek out approaching U-boats and for reinforcement of convoys under attack.

[3] The first requirement was met with the commissioning of Audacity, the first merchant aircraft carrier, the second by reinforcing the escorts and by the formation of an anti-submarine Hunting Group at Gibraltar, which would sweep ahead of a homeward bound convoy, to attack and destroy patrolling U-boats.

[5] The fighters were usually split into standing patrols of two aircraft, which flew over the convoy for about two hours, searching for U-boats and Condors, the danger mainly coming from deck landings.

[6] On 8 November, Kampfgeschwader 40 (KG 40) sent six Condor reconnaissance bombers to locate Convoy SL 91, bound for Liverpool from Freetown, Sierra Leone.

[9] A U-boat hunter group of Force H destroyers from Gibraltar, comprising HMS Croome, Gurkha, Foxhound and Nestor sailed independently.

Seeräuber was an ad hoc group, as the previous Gruppe Steuben, had disbanded following a fruitless pursuit of southbound Convoy OS 12.

[15] The pack had orders to sink Audacity at all costs and was reinforced later by three more boats; U-108 sank a Portuguese freighter sailing independently on 14 December.

[19] U-127 was detected on a routine anti-submarine sweep by a Short Sunderland from Gibraltar late in the day; next morning it was detected on Asdic by Nestor and sunk at 11:00 a.m.[3] At noon on 16 December, Convoy HG 76 was sighted and its position reported by a Focke-Wulf Condor of I/KG 40 patrolling from Bordeaux, which guided U-108 to the convoy to begin reporting its position to other U-boats.

Just after 9:00 a.m. a Martlet from Audacity sighted a surfaced U-boat about 20 nmi (37 km; 23 mi) from the convoy and circled over the area for the escort ships to gain a good radar fix; a corvette made an Asdic attack to no apparent effect.

At 12:47 p.m. on 17 December, Stanley sighted U-131 on the surface and Walker ordered a Martlet to attack while Stork, with Pentstemon and the three destroyers, made their best speed to the location.

Stork following behind, swung behind the stern of Stanley, gained an Asdic contact and dropped a pattern of depth charges, then turned after 0.5 nmi (0.93 km; 0.58 mi) to attack again.

The ship fired on the U-boat, illuminated it with snowflake Flares and managed to ram it just forward of the conning tower, scraping over the hull of the submarine.

After the last patrol, the commander of Audacity ordered the ship out of the convoy 10 nmi (19 km; 12 mi) to the starboard as usual but no escorts could be spared.

[27] During 22 December, U-71 and U-751 remained in contact, to be joined by U-125 (en route to America), while Convoy HG 76 was reinforced by the destroyers HMS Vanquisher and Witch.

At 10:54 a.m. a Liberator of 120 Squadron, 19 Group Coastal Command based at RAF Nutts Corner in Ireland (750 nmi (1,390 km; 860 mi) away) arrived over the convoy and saw off a Condor.

[19] On 23 December, Dönitz, shaken by the loss of five U-boats and the lack of success against the convoy, called off the attack, U-67, U-107, U-108 and U-751 returned to bases in France.