Operation Stonewall

Second World War
Part of Operation Stonewall of the Atlantic campaign
The Bay of Biscay
Date 26–27 December 1943 Location Bay of Biscay 45°30′N 04°24′W / 45.500°N 4.400°W / 45.500; -4.400 Result Allied victory
Belligerents
Germany Italy Japan	Britain US Canada Australia New Zealand Czechoslovakia Brazil
Commanders and leaders
Karl Dönitz	Ralph Leatham
Units involved
Befehlshaber der U-Boote (Commander, U-boats) Marine-Gruppenkommando West (Naval Group West) Luftwaffe (Fliegerfuhrer Atlantik)	Royal Navy US Navy (ships and aircraft) Royal Canadian Navy Royal New Zealand Navy Royal Air Force Royal Canadian Air Force Royal Australian Air Force Brazilian Air Force Czechoslovak Air Force (in British service)
Casualties and losses
1 blockade-runner 1 Destroyer 2 torpedo boats 1 U-boat	2 destroyers
Neutral ships from Ireland and Spain rescued German survivors

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 4:07 p.m. Liberator GR Mk V "H" of 311 (Czech) 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 HMS Glasgow and Enterprise of Operation Stonewall. In the Battle of the Bay of Biscay one of the destroyers and two torpedo boats were sunk 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.