This was an Allied naval operation to intercept and destroy German blockade runners off the western coast of German-occupied France (12/28 December 1943).
From the start of World War II the Allies had maintained a blockade against any German import of seaborne goods. Although rich in many basic industrial materials, Germany was in a similar position to the UK as a nation which could not produce some essentials, such as rubber, tin and tungsten. Until its 'Barbarossa' invasion of the USSR in June 1941, Germany was able to evade the worst effects of the naval blockade by use of the Trans-Siberian Railway, which allowed large quantities of materials to be transported from the Far East. Once this route had been closed by the German attack on the USSR, German and Italian ships, otherwise stranded in the Far East, were used as blockade runners in an effort to bring in these essentials to ports in occupied France. Although an organised interdiction against these blockade runners could not be set up until December 1943, several ships were intercepted and sunk in the Atlantic and Indian Oceans, and in fact few achieved successful homeward runs, in some bases passing through the 'Barrier' and 'Freecar' sea and air cordons.
After he had received a report indicating that Osorno, the first of five expected blockade runners, had broken through the 'Barrier' and 'Freecar' patrols in the between Natal and Freetown, Admiral Sir Ralph Leatham, the British commander-in-chief Plymouth, began 'Stonewall'. The New Zealand light cruiser Gambia and British light cruiser Glasgow were ordered to depart Plymouth and operate from Horta in the Azores island group to patrol the area to the north of these Portuguese islands.
From Horta the two cruisers established a continuous patrol, relieving each other for fuelling from an oiler at Horta. Nos 15 and 19 Groups of Air Marshal Sir John Slessor’s RAF Coastal Command and the US Navy’s 7th Fleet Air Wing, operating in the North Atlantic and in the Bay of Biscay, were also alerted, as too were other commanders and forces at sea.
On 16/17 December the 6,591-ton Osorno passed undetected through the US/Gibraltar convoy route and on 19 December threaded her way through the US/UK route, passing the course of the ON.215 convoy, escorted by the Canadian Escort Group C4, for a short distance and following the HX.270 convoy, supported by Captain D. S. McGrath’s British Escort Group C1 with the escort carrier Tracker, at a distance of one day while the SC.149 convoy, escorted by the British Escort Group B5, followed, also at a distance of one day.
The 2,729-ton Alsterufer, the next blockade runner in this German sequence, passed through the USA/Gibraltar route on 20 December just behind Captain L. C. Ramsey’s Task Group 21.16 (escort carrier Block Island and destroyers Paul Jones, Parrott, Bulmer and Barker) behind the westbound GUS.23 convoy and not far from the eastbound UGS.27 convoy.
On 21/22 December Osorno changed course for the Bay of Biscay and crossed, in a period of less than one day each, the courses of the KMF.27 convoy escorted by the British 4th Support Group, and the MKS.33/SL.142 convoys escorted by Captain W. W. R. Bentinck’s British Escort Group B4 including the escort carrier Fencer, while Captain J. R. Dudley’s TG21.15, with the carrier escort Core and four destroyers, and Captain A. J. Isbell’s TG21.14, with the escort carrier Card and three destroyers, was hunting the 'Borkum' wolfpack formed specially to cover the route of the blockade runners.
Gambia and Glasgow were already in Osorno's wake. Alsterufer remained some distance from the CU.9 convoy to the east, TG21.16 to the south-east and the SC.149 convoy to the north. On 23 December, aircraft from Card spotted a suspected blockade runner, and there were further reports of a flotilla of destroyers escorting another merchant ship to the west from France. Gambia and Glasgow, supplemented by the light cruiser Enterprise, formed a cordon to effect an interception. Aircraft attacked the flotilla, now escorting the incoming merchant ship, Osorno, reporting a hit and a near-miss on the vessel, which was subsequently beached and unloaded offshore. More warships (the British light cruiser Penelope and cruiser minelayer Ariadne, supplemented by four Free French destroyers) joined the patrol to intercept another blockade runner, and aircraft of RAF Coastal Command acted in close co-operation.
Before the Allied ships and an RAF strike force could make contact, the shadowing Czechoslovak-crewed bomber attacked with bombs and rockets and set Alsterufer on fire, the German crew being rescued by four Canadian corvettes.
A force of German destroyers and torpedo boats had set out to meet and escort Alsterufer, and Glasgow and Enterprise now attempted to intercept them. Guided by shadowing aircraft, the cruisers intercepted eight destroyers in the early afternoon of 28 December and exchanged fire with them. Despite accurate German gunfire and torpedoes, effective German evading action and an attack with guided bombs by a Luftwaffe aircraft, the British ships maintained contact. The German warships divided into two groups and the cruisers pursued one of these. By 16.00, the destroyer Z 27 and the torpedo boats T 25 and T 26 had been sunk, and one had escaped although she too had suffered damage.
About 230 survivors were picked up by British minesweepers, a small Irish steamer and Spanish destroyers. Glasgow, Enterprise and Ariadne now returned to Plymouth, and Penelope to Gibraltar.
More blockade runners from the Far East were expected, so Gambia and Mauritius maintained the cruiser patrol to the north of the Azores islands group for the next three days. Gambia then returned to Plymouth on 1 January 1944. Three more German ships were sunk on 3/5 January 1944 by US Navy patrols in the South Atlantic. These were the Germans' last attempted blockade runners as, by the autumn of 1944, the German armies were retreating headlong out of France and the French ports were no longer open to incoming Axis ships.