Operation Stonewall was an Allied naval and air operation in the Second World War from 26 to 27 December 1943, to intercept blockade-runners sailing to German-occupied France through the Bay of Biscay. Operations Barrier and Freecar, by the Allied navies and the Brazilian Air Force, had taken place in the south- and mid-Atlantic. The ships were tracked by OP-20-G (US Navy) and British (Government Code and Cypher School (GC&CS) at Bletchley Park) code-breakers, which decrypted Japanese machine cyphers and German Enigma machine transmissions to U-boats (Shark cypher) and blockade-runners (Sunfish cypher).
At the west end of the Bay of Biscay, Royal Navy and Allied ships, with Coastal Command aircraft of Operation Stonewall hunted the blockade-runners, assisted by convoy Escort Groups and support groups diverted from nearby convoys. Osorno and Alsterufer were the first two blockade-runners of the late 1943 – early 1944 season. Osorno evaded interception and was escorted into the estuary of the Gironde by German destroyers and torpedo boats (small destroyers).
On 27 December, Alsterufer was spotted by a fighter from an American escort carrier, then attacked by Australian, British and Canadian, Coastal Command, Sunderland flying boats but suffered little damage. At Liberator GR Mk V "H" of 311 (Czechoslovak) Squadron made a low-altitude attack on Alsterufer with rockets and bombs, setting the ship on fire. Alsterufer sank the next day and 74 survivors were rescued 48 hours later by Canadian corvettes.
The German destroyers and torpedo boats that had escorted Osorno to port sailed to rendezvous with Alsterufer, the Germans being unaware of the bombing of the ship. Using Enigma decrypts of their positions, the German ships were bombed by US Liberators and then intercepted by the cruisers and of Operation Stonewall. In the Battle of the Bay of Biscay one of the destroyers and two torpedo boats were sunk in battle during a severe storm. Sailings of blockade-runners from France were cancelled and three runners from Japan were sunk by the US Navy in the south Atlantic in January 1944.
Background Allied blockade of Germany
From the start of the war on 3 September 1939, the Allies proclaimed a blockade of Germany to prevent the import of goods. Germany had no rubber, oil, tin and tungsten. Until Operation Barbarossa the German invasion of the Soviet Union, it evaded the blockade via the Trans-Siberian Railway. After the supply route was closed at the start of Barbarossa and after the Japanese entry into the war, German and Italian ships were stranded in Japan and Japanese-occupied Singapore. The ships were used as blockade-runners, sailing to ports in occupied France after mid-1940, when Germany had taken control of the European coast from Norway to the French–Spanish border. From April 1941 to May 1942, 32 ships tried to reach France and 14 succeeded. In 1941 and 1942, German and Italian ships brought in of commodities and exported to Japan. From August 1942 to April 1943 fifteen ships tried to run the blockade and four got through.
Blockade-running
After sailing from Japan, through the Pacific and the Indian Ocean to the Cape of Good Hope, blockade-runners kept radio silence and passed rearranging points at planned times. When a ship was due, U-boats and aircraft were barred from attacking merchant ships in a lane in the mid-Atlantic, to the north-east from a line level with the Canary Islands, east of the Azores and then east to Bordeaux. Escorts were laid on through the Bay of Biscay and the ships received occasional support further out from U-boats. After the cargo has been discharged, the ship was re-fitted for the next journey.
More accommodation was built for crew and passengers, decks were reinforced, guns and ammunition stores were installed. A minimum of four scuttling charges of up to were placed in the bottom of the hull and armed when the ship sailed with 7–9-minute fuzes; the crew kept their belongings ready in case they abandoned the ship. The vessel went into dry dock to have the hull cleaned to increase its speed and the ship underwent sea trials, sometimes incorporating the delivery of goods to Bassens or to another Biscay port. When ready to sail, the ship waited in the Gironde for an escort of minesweepers. Early in the war, the sailing schedule was little different from a peacetime commercial service.
1943–1944 season U-boats were used to transport small amounts of commodities in 1943 while bigger transport submarines were built but by winter German industry would need several shiploads of rubber and other cargoes. Despite the risks several ships would have to be despatched from Japan. There were five motor vessels in Japan and it was thought that if they left at fairly frequent intervals, the Allies might be distracted by the hunt for one and let another slip through their blockades. The ships would be on their own on the voyage but the run through the Bay of Biscay could be assisted by surface ships and aircraft. The five ships would carry of rubber and other goods and sail at intervals that would allow the Biscay escort forces to meet one about out from Bordeaux, escort it to port and then sail to meet the next one. The best time for the attempts to run the blockade would be midwinter 1943–1944.
(, code-name , Paul Hellmann) of the Hamburg America Line (HAPAG) with of rubber, of tin and of tungsten, sailed from Kobe on 2 October, disguised as the British ship Prome, rounding the Cape of Good Hope on 15 November. Osorno was followed by the refrigerated cargo ship (reefer) (2,729 GRT, code-name , Piatek) of the Robert M. Sloman Jr. line of Hamburg, carrying of tungsten, a year's worth of consumption in the German war economy. sailed third on 4 October 1943 from Yokohama; and departed later in the month. Allied spies reported the arrival of the first three ships at Saigon (now Ho Chi Minh City), raising the alarm.
Ultra
The defeat of the German U-boat offensive in the Battle of the Atlantic in 1943 was followed by the last attempt by the Germans to pass blockade-runners through the Bay of Biscay to and from the Japanese empire. From May 1943 decrypts of Japanese diplomatic wireless traffic revealed to the Allies that the losses of the 1942–1943 season had not deterred the Axis from making another attempt in the autumn. Seven merchant ships were to sail from Europe carrying of exports and that the Germans were building special U-boats to import of goods from Japan in 1943. In July and August, photographic reconnaissance and agent reports from the French Atlantic ports that sailings for the far East were being prepared and by 6 September it was clear that seven ships were close to sailing.
On 4 October, after the blockade-runner Kulmerland had been hit by Allied bombers, a signal from the Japanese Ambassador in Berlin showed the Allies that the export programme had been cut to because of the bombing. On 18 July the British and Portuguese reached a basing agreement for the Azores, which came into force on 8 October and which had the potential to deter the Axis from trying to run the blockade. On 23 October, the Germans introduced new W/T methods for signalling between U-boats and blockade-runners in the Bay of Biscay and in early November Dresden, thought to be a blockade-runner, struck a mine. The British thought that five ships were preparing to leave the Bay and that four ships were preparing to return from the Far East. Later in November, another decrypt from the Japanese Ambassador revealed that the German export programme had been reduced again, to . US Navy patrols in the South Atlantic were increased.
Prelude Allied intelligence
The Ministry of Economic Warfare in London knew that the winter would be the best time for blockade-runners and photographic reconnaissance revealed that the number of German warships in the French Biscay ports had been increased. Enigma decrypts and agent reports from the Far East alerted the Allies. Evidence that the new round of departures from the Far East had begun was found in an Ultra decrypt of 16 November, prohibiting U-boat attacks west of a line in the south Atlantic.
The Naval and air commanders were told that a northbound blockade-runner and possibly another eight were approaching, including Osorno and Alsterufer. Little was revealed by OP-20-G, the US Navy (USN) code-breaking organisation, until 26 November, that on the day before the U-boat restrictions ("") in the south Atlantic had been imposed further north on 1 December. On 26 November the Italian ship Pietro Orseolo sailed from Bordeaux to Concarneau on the south Brittany coast and was attacked by aircraft from Coastal Command on 1 December to no effect.
Operation Barrier Operation Barrier began with Task Force 41 (TF.41) comprising five task groups, of a cruiser and a destroyer each, three of which were permanently at sea and USN aircraft patrols from Natal in Brazil, with Brazilian Air Force patrols from Recife (at war with Germany and Italy since 22 August 1942) and flights by USN patrol bombers from Ascension Island on 1 December. More information was received by the Allies on 5 December that the restrictions were in force north of the equator from the next day. Osorno was spotted on 8 December by Liberator B-8 of VPB-107 from Ascension but TG.41.4 (the cruiser and the destroyer ) were chasing another contact which turned out to be a Greek independent, then began a hunt for a U-boat and Osorno escaped. The Admiralty signalled the importance given to preventing the arrival of blockade-runners on 12 December and the Royal Navy light cruiser left on patrol from the Azores. Searches to the north-west found nothing but Osorno had been sighted by whose report was decrypted by OP-20-G on 13 December.
Operation Freecar Freecar began soon after Barrier with and both armed merchant cruisers, the French cruiser and the Italian cruisers Abruzzi and d'Aosta. Barrier and Freecar were suspended, letting Alsterufer pass unseen. On 18 December, a Sunfish message sent on 13 December to Osorno and Asterufer was decrypted and on 22 December a decrypt of the U-boat Shark cypher showed that the U-boat restrictions were in force west of the Bay of Biscay.
Operation Stonewall Plymouth Command Coastal Command prepared Halifax and Liberator bombers to attack the blockade-runners as they crossed the Bay of Biscay. The Royal New Zealand Navy (RNZN) light cruiser HMNZS Gambia, recently refitted, arrived at Plymouth from Scotland on 5 December 1943. Gambia was to join Glasgow and Enterprise under the command of the Commander-in-Chief Plymouth (Admiral Ralph Leatham) for operations against blockade runners. U-boats were sailing in distant waters which required more signals from Admiral Karl Dönitz (, BdU, Commander, U-boats) about blockade-runners. The Shark cypher for U-boats was often being decrypted quickly by the Government Code and Cypher School which then broke the Sunfish Enigma key used by the blockade-runners.
Osorno +Convoy codes Code Route CU Curaçao/New York to UK (tankers) GUS Port Said to US Slow HX Halifax to UK KMF UK to Mediterranean Fast KMS UK to Mediterranean Slow MKS Mediterranean to UK Slow ON Outward North (UK to US) OS Outbound South (UK to Freetown) SC Sydney/Halifax/New York to UK SL Freetown to UK UGS US to Port Said/Gibraltar