This was a British naval attack on German convoys off the west coast of Brittany in German-occupied France between Brest and La Rochelle (30 July/3 August 1944).
During July 1944 it became clear that there was an increasing likelihood of a major Allied land success in the Normandy lodgement, leading to an Allied break-out and advance primarily to the east through France toward the Low Countries and western Germany. The Allies felt that this would compel the Germans to evacuate some if not all of their naval bases along the coast of the Bay of Biscay, and in advance of this would start to relocate substantial numbers of U-boats from bases in the Bay of Biscay to bases in German-occupied Norway so that they would still have access, albeit more limited, to the Atlantic and considerably greater strength against the convoys passing through Arctic waters to and from the northern USSR. In this eventuality the Admiralty planned to reroute transatlantic convoys considerably farther to the south to place them near, if not beyond, the limits of the relocated U-boatsí radius of operation, and at the same time bring their routes within the radius of Allied anti-submarine aircraft based in the Azores islands group.
It was likely, therefore, that the main weight of the air campaign against the U-boats would come to be borne by the anti-U-boat air patrols carried out by Air Vice Marshal S. P. Simpsonís No. 18 Group rather than Air Vice Marshal B. E. Bakerís No. 19 Group, and Air Chief Marshal Sir William Sholto Douglas, heading RAF Coastal Command, thus decided to reinforce the former from the latter. The changes took place gradually, and were not completed until the end of September.
The Germans in fact started to redistribute their U-boats in the Bay of Biscay at a time early in August: initially there was a considerable southward movement from Brest, Lorient and St Nazaire to La Pallice and Bordeaux, and five more U-boats were ordered into the English Channel.
Coastal Command immediately moved No. 19 Groupís patrols to cover the southward movement, while Home Fleet cruisers and destroyers under Vice Admiral F. H. G. Dalrymple-Hamilton, commanding the 10th Cruiser Squadron, started to operate in the Bay of Biscay to stop any attempt by the surviving German surface warships (four destroyers at La Pallice and Bordeaux) to escape.
A series of Coastal Command sweeps, raids by Air Chief Marshal Sir Arthur Harrisís Bomber Command, and searches and bombardments by warships now became more frequent on and off the coast of the Bay of Biscay. The British forces gained many successes, a notable event on 6 August being an attack off St Nazaire by elements of Force 26 (light anti-aircraft cruisers Bellona and Diadem, destroyers of the 10th Destroyer Flotilla, and three lighter warships of the 11th Escort Group) on a convoy of two small coasters, a cablelayer and the aircraft repair ship Richthofen, escorted by five warships, and either sank or severely damaged all of them.
Two days later No. 19 Groupís Beaufighter Strike Wing destroyed an entire force of four minesweepers in the same waters. Two more naval squadrons, comprising the light anti-aircraft cruiser Diadem and light cruiser Mauritius, each accompanied by a pair of destroyers of the 10th Destroyer Flotilla (Force 28 and Force 27 respectively), supplemented Force 26 in ĎAssaultí. On 12 August Force 28 co-operated with the Beaufighter Strike Wing in sinking a 7,087-ton Sperrbrecher (mine destructor ship) off La Rochelle. Three nights later it was the turn of Force 27, which added another Sperrbrecher to the tally of German ships sunk off La Pallice, and seriously damaged the torpedo boat T 24 and two minesweepers.
This type of operation continued by day and night right through August, with occasional pauses imposed only by the weather.
In an attempt to counter the British surface ship sweeps, the Germans redeployed three U-boats to ambush them, but Oberleutnant Wolfganf Reisener’s U-608 and Oberleutnant GŁnther Keller’s U-981 were soon sunk. On 16 August the Germans realised that with the Allied armies on the outskirts of Brest, Lorient and St Nazaire, they had to remove their U-boats from those bases. Except for three U-boats despatched to the Indian Ocean and eight U-boats sent to patrol in the North Channel and Bristol Channel, every U-boat in the Bay of Biscay bases which could be made fit for sea, and some which were inward bound from the Atlantic or more distant waters overseas, were instructed to head to Norway. Three boats were left at Bordeaux, two at Lorient and one at La Pallice, and these were scrapped or scuttled before the Allies took the ports.
To divert the attention of Allied anti-submarine forces from this sizeable relocation, the Germans sent a number of U-boats into the English Channel and the waters round the UK, and their appearance contributed to the safe passages accomplished by all the boats bound for Norway.
In the Bay of Biscay the climax to the offensive came between 22 and 27 August. Then the light cruiser Mauritius and the destroyers Ursa and Canadian Iroquois fell in with and totally destroyed a force of seven patrol vessels off Belle Ile. No. 19 Groupís Beaufighter Strike Wing sank the destroyer Z 24 and torpedo boat T 24 (the only two of the four surviving warships of these types which could be made fit for sea) anchored off Le Verdon, and a devastating series of British and US bomber raids on the harbour of Brest destroyed six large ships (23,477 tons) and nine smaller vessels.
During the three weeks of this offensive the German losses in the Bay of Biscay totalled 12 U-boats (U-736, U-608, U-385, U-981, U-270, U-618, U-107, U-621, U-984, U-180, U-445 and U-667), 11 large ships (58,835 tons), one destroyer, one torpedo boat, and 53 coasters, minesweepers, patrol vessels and miscellaneous craft. The damage to the German minesweeping capability also led to the loss of many vessels which might otherwise have survived. Of the 12 U-boats sunk, four fell victim to surface ship attack, three to air attack, three to combined surface ship and air attack, and two to mines.
Thus by 27 August the German naval strength in the Bay of Biscay had almost ceased to exist, although the Germans could take comfort from the fact that no fewer than 31 U-boats, in the form of 22 from the Bay of Biscay ports and nine directly from the English Channel and South-Western Approaches, had been relocated to Norwegian bases.
On 18 August Adolf Hitler ordered the German forces to leave southern and south-western France, although he also ordered that Brest, Lorient, St Nazaire, La Pallice and the Gironde ports were to be held as Ďfortressesí. The Allies were initially content merely to invest the ports to the south of Brest, through the use primarily of French resistance forces, and it was to them that Bordeaux fell on the last day of August. But the fact that the Germans were still holding the northern and southern shores of the Gironde river estuary to the north-west of Bordeaux meant that the Allies could not use the port, and the surrender of the last pockets of German forces along the coast of the Bay of Biscay did not take place until the end of the war, when all surviving warships and merchant vessels in those harbours were scuttled.
The US forces wanted Brest for the delivery of reinforcements and supplies, so on 25 August there started a heavy land, sea and air assault on this very strongly held base. The British battleship Warspite, damaged by a mine on 13 June, had been repaired and arrived off Brest on the day of the assaultís beginning, and began a gunfire bombardment of the German coastal defences at a range of 30,000 yards (27430 m) with observation and fire correction provided by a special mobile army unit. In spite of the severity of the assault, the Germans held out to 18 September. The Allies then found the harbour areas littered with sunken ships, and so badly damaged were the docks, quays and jetties that no substantial use could be made of the port for many weeks. As, however, their advance had meanwhile carried the Allied armies far to the east, Brest had in fact lost a great deal of its importance.