Operations Tunnel and Stonewall

The recurrent naval actions throughout World War II in the English Channel and Bay of Biscay don’t get much attention. Most of them revolved around either German attempts to intercept British shipping or the British trying to intercept escorted German blockade runners, with mixed results in both cases. The actions in late 1943 are the most well known of these battles and the subject today. There had been more isolated entanglements before, notably on 10 May 1942 when the German raider Stier and two torpedo boats were intercepted — Stier escaped to the Atlantic while both of its escorts were sunk — but it didn’t become a more organized effort for the Royal Navy until much later.

In dealing with these German blockade runners and coastal convoys the Royal Navy had been somewhat successful; between August 1942 and May 1943 only four of fifteen got through. Nevertheless the numbers were still too high for the British given the valuable cargo they were carrying, and they began Operation Tunnel in early October 1943, a series of sweeps by ad hoc naval task forces covering the western end of the English Channel. It didn’t take long for these task forces to see action.

The Action off Les Triagoz

On the night of 3 October a British force of five destroyers (the escort-destroyers Limbourne, Wenslydale, and Tanatside and the fleet-destroyers Ulster and Grenville) under Commander Conrad Alers-Hankey was cruising off Les Triagoz trying to interdict a coastal convoy when they were detected by shore-based German radar. The German 4th Flotilla consisting of four Elbing-class torpedo boats (T22, T25, T27, and flagship T23) under the command of Franz Kohlauf was escorting that convoy when Kohlauf was notified of their presence (not to be confused with the puny E-boats the Elbing-class were the size of Allied destroyers). Kohlauf broke off with his force to shadow the would-be attackers. The British ships were faintly silhouetted against the night sky while the German ones had the dark Breton coastline behind them allowing Kohlauf to get close and maintain contact.

Type 39 “Elbing-class”
HMS Grenville in May 1943
Korvettenkapitän Franz Kohlauf

Kohlauf’s flotilla were able to make a torpedo run (all of which missed), break off, and conduct a second attack completely unseen until finally the pulses from a directional radar on one of the German ships was detected by HMS Tanatside. Hankey now realized what was going and ordered his force to turn away, avoiding the second torpedo salvo and then disappearing into the darkness. Hankey tried to surprise the Germans from a different direction only for his whole force to be illuminated by enemy star shells.

A chaotic torpedo and gunnery exchange ensued as the two lines of ships were on a slowly converging parallel course. While all three of the Hunt-class escort-destroyers at Hankey’s disposal were Type III’s (which had torpedoes unlike previous Hunts) their slow speed was a decisive disadvantage. While the battle doctrine of Tunnel had called for a tight single-file formation of ships the two more powerful destroyers under Hankey’s command, HMS Ulster and HMS Grenville, quickly ran far ahead of the three Hunts and came under accurate fire. Right after firing her torpedoes Grenville was hit twice, one penetrating the hull foreword and the second hitting the lattice mast; the blast turning the entire crew of “X” turret into casualties and igniting a cordite bag. Her quarterdeck now engulfed in flames Grenville fell out of column leaving Ulster alone to take on an entire German flotilla. She launched her own torpedo salvo but the German ships turned away and avoided them before reforming their battle line and peppering the sea around Ulster with naval gunfire. Ulster was hit twice: one on the waterline flooding her foreword magazine and the other just abaft “A” turret. She fired another torpedo salvo before turning away along with Grenville to rejoin the three Hunts, T23 in hot pursuit. The British force managed to escape into the night, but not before a friendly fire incident to cap off the evening when Hankey’s own flagship HMS Limbourne mistook Grenville for a German ship in the darkness. Combined Grenville and Ulster had suffered 18 wounded and 2 killed; despite their heavier armament the Germans had gotten the better of the gunnery duel.

This had been a very poor start to the renewed British blockade efforts; although none of them were lost (and no torpedoes from either side hit) all but one of Hankey’s ships suffered serious battle damage while his force inflicted only splinter damage on the German side. In retrospect the worst thing about the action was that the British learned nothing from it, their solution was just to send out task forces with more and better ships rather than change their doctrine, coordinate better, or improve their flotilla training. The Royal Navy was reinforced in this belief by false claims that Hankey’s task force had dealt the Germans significant damage. It was a lesson they would have to learn the hard way.

The Battle of Sept-Îles

The German blockade runner Münsterland arrived in Brest harbor on 9 October. Since the begging of the war Münsterland had evaded Allied capture, sailing from Latin America to Asia, and she was on her way back to Germany from the long voyage carrying valuable strategic materials including rubber, tungsten, and chromium. Thanks to Ultra decrypts the British were aware in detail of Münsterland’s mission and Plymouth Command organized a strike force under Captain George Voelcker consisting of the light cruiser HMS Charybdis (Voelcker’s flagship) and two fleet (Grenville, Rocket) and four escort-destroyers (Limbourne, Wensleydale, Stevenstone, and Talybont) to be put on stand-by. The Münsterland finally departed Brest for the English Channel on the evening of 22 October, and the Royal Navy rushed to intercept. From Voelcker’s strike force only the three Hunt-class escort-destroyers were from the same flotilla and their senior officer, Commander Commander W. J. Phipps, had only been in command for two days, and had only been briefed on Operation Tunnel a few hours earlier, all factors hampering coordination.

The blockade runner Münsterland
HMS Limbourne
HMS Charybdis
Charybdis at sea

Six minesweepers and two radar-equipped patrol boats made up the close-escort for Münsterland while the torpedo boats of 4th Flotilla (T22, T23, T25, T26, and T27) again under the command of Franz Kohlauf joined the escort enroute and took up positions to the northeast, ahead of the convoy. Voelcker’s strike force reached the southern side of the English Channel after midnight and began sweeping toward the western end of the channel to engage the German convoy off Les Sept Îles, a small archipelago north of Brittany. Voelcker was under very specific rules of engagement; first he was to keep his force in a single line ahead formation with only the 271 and 272 10-centimeter surface search radars active, all other radar and sonar had to remain silent to reduce the risk of detection. He was supposed to close within 6,000 yards before firing star shells to illuminate the enemy and commencing action unless he was detected first. Unfortunately for the Royal Navy the Germans had seen enough of Tunnel to anticipate all of this.

Voelcker’s strike force was near Les Heaux De Brehat (a rock islet with a lighthouse on it) when T25 detected it with hydrophone moving northeast of the convoy, and Kohlauf took his 4th Flotilla toward the contact. The three Hunt-class escort-destroyers intercepted radio transmissions between the German ships but Voelcker didn’t react. The search radar on Charybdis finally detected the flotilla heading toward the strike force on a converging course and increased speed but visual confirmation was difficult despite the bright moonlight, as was the case at Les Triagoz the 4th Flotilla had a darker backdrop to obscure its silhouette (this time a rain squall).

The Germans intercepted messages indicating they had been sighted, the British concluding they had lost the opportunity for a surprise torpedo attack. Voelcker gave an order for his force to turn starboard, but HMS Limbourne lost track of the flagship and the remaining destroyers — picking up new indications of enemy forces, ambiguous radar returns, and undecipherable signals — completely lost formation. Kohlauf spotted Charybdis’ silhouette against the lighter northern horizon just 2,000 yards away. Believing he had been spotted and was about to be attacked he ordered a battle turn away to starboard. As they came about T23 and T26 emptied their torpedo tubes in the direction of Charybdis. Still relying on radar Charybdis fired a star shell to illuminate the area, only for it to burst above the clouds and brighten the overcast sky instead.

Limbourne plotted a contact off her port bow and assuming it was hostile fired her own rockets to illuminate the area while the fleet destroyers passed by her stern. The lookouts on Charybdis suddenly spotted the foaming torpedo tracks heading toward them. The cruiser turned hard to port but it was too late, and a torpedo slammed into its port side causing her to lose power and heavily list. The remaining torpedo boats still conducting their turn away fired their torpedos, except for T25 due to the hesitation of her new torpedo officer. A few minutes later another torpedo struck Charybdis’ port side and and a second struck Limbourne; within five minutes the port side deck of Charybdis was underwater. HMS Wensleydale and Grenville barely avoided the same fate with evasive action.

With Charybdis out of action Grenville’s captain, Lieutenant Commander Roger Hill, was now the senior officer but he didn’t appreciate this fact until much later. The other destroyers chaotically broke off in the opposite direction. By the time the destroyers fled, regrouped under Lt-Cmdr Hill, and returned to the battle over an hour after the torpedo attack Charybdis had already sunk, although Limbourne was still afloat. Hill rescued the survivors from Charybdis, 107 men in total; 464 officers and men from the cruiser had been killed including Voelcker himself. Attempts to tow Limbourne failed and she was finished off with torpedos from HMS Rocket and HMS Talybont after the surviving crew were offloaded, she had lost 42 men. Kohlauf monitored the British destroyers via radar from a distance while Münsterland safely arrived in Saint Malo. Hitler subsequently rewarded him with a Knight’s Cross of the Iron Cross for his actions off Les Sept-Îles.

The second major action since Operation Tunnel began had been a total disaster for the Royal Navy. While they had gotten away with similar weaknesses at Les Triagoz, this time they lost two warships and 506 sailors without so much as firing a shot at the enemy or coming close to the blockade runner. Sept-Îles was in fact the last major victory of the war for the Kriegsmarine.

The Battle of the Bay of Biscay

Münsterland’s success in reaching home waters encouraged the Germans to order two more loaded ships waiting in the Far East to leave for Europe, codenamed Operation Bernau. Again thanks to Ultra the British were aware of what was going on and not long after the blockade runners departed the Vietnamese port city of Saigon the British launch Operation Stonewall, which was similar to Tunnel but covering the entrance of the Bay of Biscay with cruiser patrols based out of the Azores. Nonetheless in late December the first of the blockade runners Osorno eluded the cruiser patrols and was met in the Bay of Biscay by a large escort force: the 8th Destroyer Flotilla (with the destroyers Z23, Z24, Z27, Z32, and Z37) under Hans Erdmenger, Kohlauf’s 4th Torpedo Boat Flotilla, and air cover from long-range JU-88 fighters. These escorts fought off air attacks on Christmas Day and Osorno was able to arrive and unload her cargo of rubber at Bordeaux, its only damage being an accidental collision with a submerged wreck in the Gironde estuary, this was in spite of the five British cruisers that were placed across the Bay and the Atlantic. The 8th Flotilla and two torpedo boats from the 4th accompanied Osorno to Bordeaux while the rest of the 4th Flotilla went back to Brest.

This was starting to become a complete embarrassment for the Royal Navy, and the next blockade runner Alsterufer, a few days behind Osorno, was already approaching from the open Atlantic. But two days later on 27 December their luck changed: Alsterufer was spotted and sunk by aircraft on her way to the French coast before she didn’t even manage to get out a message that she was under attack, although she resisted fiercely with anti-aircraft fire. (If you want to read more about the Alsterufer, you can find the interrogation of its survivors here.)

After departing Brest and the Gironde respectively, Kohlauf and Erdmenger’s forces were waiting to escort Alsterufer as she headed for France, completely unaware that the blockade runner was at the bottom of the sea, as the British light cruisers HMS Glasgow and HMS Enterprise (under the combined command of Captain Charles Clark onboard Glasgow) enroute from the Azores now raced to intercept them; again information from Ultra was crucial for the British. By noon of the next day (28 December) the 4th and 8th flotillas had met at sea, and combined under Erdmenger’s command and began heading toward France. The Germans still had no idea of what happened to Alsterufer (or that they had been spotted by aircraft from the American carrier USS Card) while the British cruiser force was fast approaching. Around noon Glasgow and Enterprise were themselves spotted and attacked by a lone German aircraft, but Erdmenger didn’t find out about it until a half hour later. By the time Erdmenger was made aware of the impending ambush, it was too late to avoid action; the British force had worked itself northeast of his position.

Alsterufer under air attack from No 311 (Czechoslovak) Squadron RAF
Korvettenkapitän Hans Erdmenger

Erdmenger was a veteran of the Norwegian campaign more than three years earlier. During the first battle of Narvik the destroyer Z21 Wilhelm Heidkamp under his command sank the Norwegian coastal defense ship Eidsvold, only for his own destroyer to be blown out from under him the next day during the second battle; actions he was awarded Knight’s Cross for. He was then given command of the destroyer Z48 from August 1941 through February 1943, followed by the command of the entire 8th Destroyer Flotilla since March 1943, but during that entire time he had not seen action against enemy ships. Thus while he was experienced on paper, it had been so long since he been in action (and never as a flotilla commander) that those experiences wouldn’t necessarily benefit him in the upcoming fight. In addition the destroyers and especially torpedo boats under his command had poor seakeeping and stability in the open winter-time Atlantic, another disadvantage for the Germans going into action.

At 1:32 in the afternoon Glasgow reported ships the German ships sixteen miles to the southwest. Captain Clark sat down for a somber dinner as he ordered an increase of speed and an alternate course to block the path home for the German force. Eight minutes later lookouts onboard Z23 spotted the British cruisers. Erdmenger’s force was now sailing south-southeast in three columns, and he ordered an immediate torpedo attack. None his ships complied due to the rough seas and extreme range. With higher speeds and a converging course Clark’s cruisers closed rapidly, and at 1:46 Glasgow opened the engagement with her first salvo at over nearly 20,000 yards away.

HMS Glasgow (left) and HMS Enterprise (right) together at anchor in 1942
Sailors clearing spent 4″ anti-aircraft cartridges from the decks of HMS Glasgow

The intial battle phase lasted thirty-three minutes as both groups ran south southeast, Glasgow and Enterprise firing salvos at the nearest destroyers, Z23 and Z27. As the range closed to 18,600 yards the Z23 in compliance with Erdmenger’s earlier orders launched six torpedoes, while both destroyers began trading gunfire with the cruisers. As the range closed further the shell fire from both sides began to straddle the other, but still no hits. Erdmenger ordered Kohlauf’s 4th Flotilla to conduct their own torpedo attack but the range-finders on his torpedo boats were so inundated by the high seas none of his ships could acquire a target, so rather than send off blind torpedo salvos he withheld their fire. Erdmenger then began to separate his forces: he ordered the 2nd Division of his 8th Flotilla to close for another torpedo attack while the 1st Division stayed in line. It was the Germans who drew first blood when at 2:06 a shell from Z32 hit Glasgow, destroying the boiler room fan intake and killing two men. Even with the constant pitching and heavy sea spray the Germans also straddled Enterprise repeatedly causing splinter damage, although none were direct hits. (it’s worth noting that the destroyers of 8th Flotilla were all “Narvik-class” Type 1936A’s with a primary armament of 5.9″ guns, cruiser grade weapons) At 2:15 after closing to 14,000 yards Z37 fired four torpedoes, but like the others they all missed.

For some reason at 2:19 Erdmenger decided to divide his forces further (a decision Kohlauf strongly disagreed with) and had his five rearmost ships (including his own flagship Z27), turn sharp to starboard and breakoff to the northwest. In response Clark separated his own cruisers, ordering Enterprise (under Captain Harold Grant) to breakoff off west to engage the northwest group while Glasgow engaged the remaining southern group now under the command of Captain Ritter von Berger onboard Z32, and included Franz Kohlauf’s flagship T23. To cover Erdmenger’s turn away to the northwest Berger’s own Z32 launched six torpedoes and Z23 launched one, while both Z32 and Z37 laid a smoke screen. At 2:28 lookouts onboard Glasgow spotted the torpedo tracks despite the rough seas, the cruiser violently maneuvering as one passed just thirty yards off her port quarter and two others down her port side.

Unfortunately for Erdmenger his flagship Z27 had botched its turn (although Vincent O’Hara argues in his book German Fleet at War that it was intentionally done to create a decoy) and was much closer to Enterprise than the rest of the northern group. She launched four torpedoes toward Enterprise at 2:28 but became the first German ship to be when 6″ return fire penetrated one of her boiler rooms and passed through an oil bunker, igniting a huge fire. Z27 launched four more torpedoes to no avail, but Z27 had lost her way from and was on a converging course with Enterprise. Berger continued leading his force to the southeast out of the action, they would have passed Glasgow’s but the cruiser turned around at 2:35 on Clark’s orders to rejoin Enterprise to the northwest. The German northern group was completely out of formation: T25, T22, and T26 were northwest of Z27’s position heading nearly due north while Z23 was off on her own between Z27 and Clark’s cruisers. It had been one hour since the British were first spotted, with the Germans divided into three areas but up to this point suffering only one ship damage, when Clark began to defeat his enemy in detail.

A post-battle sketch of T25 and T26 being shelled from the view of Z27 by a German survivor

At 2:54 the torpedo boat T25 was hit by a series of shells from Glasgow on her aft torpedo tubes and flak platforms, severing her oil lines and bringing the engines to a stop. Another projectile exploded near her foreword funnel, blowing it and her main mast overboard. At T22 attempted to assist her sister-ship and fired six torpedoes at the cruiser, but they were so far off target the lookouts onboard Glasgow never even spotted them. With geysers from the 6″ fire rapidly approaching T22 made smoke and sped away to the southeast. Glasgow shifted fire to T26 and hit her boiler room. As T22 passed T26 she laid another smokescreen to protect it before her escape. As Clark was dealing with the torpedo boats Grant aboard Enterprise dealt with the two destroyers in the northern group, at 3:06 firing his torpedoes at Z27 while Z23 tried to obscure herself and the flagship with a smoke screen. The German destroyers got a rest bit when Enterprise temporarily disengaged to clear a gun jam and fix some fire-control defects. Z23 tried to come alongside Z27 but Erdmenger ordered her to escape instead.

Grant’s ship then rejoined the battle and assisted Clark at a distance in sinking T26, which was finished off by a torpedo from Enterprise. While trying to catch up with Glasgow, Grant’s ship encountered the heavily damaged T25 which he also finished off with a torpedo. Finally, Clark found the crippled Z27 drifting in the rough Atlantic with all of her guns silent. Glasgow closed to point-blank range fired rapid salvos, detonating Z27‘s magazines. The engagement was over by 5:00. Satisfied with his afternoon’s work and with limited ammunition and fuel remaining, Clark had his force make for Plymouth. From the three German ships sunk: there were 74 survivors from Alsterufer, 90 survivors from T26, 100 survivors from T25, and 93 survivors from Z27; among the dead of Z27 was Erdmenger and his entire staff, while the survivors were picked up by German, British, Spanish, and Irish ships. The two surviving ships of the German northern group, T22 and Z23, managed to reunite and reach Saint Jean de Luz, a French harbor close to the Spanish border. Berger had sent the torpedo boats under Kohlauf to Brest while he took his destroyers back toward the battle area. They spotted the British cruisers but did not engage, and then returned to the Gironde that night, the total German death toll having been nearly 400.

Erdmenger had made a fatal mistake in separating his forces and engaging in long-range torpedo attacks instead of massing his ships for a single mass-strike, or at least a more determined attempt to breakoff action altogether.


With the mitigation of Osorno’s safe arrival, Operation Bernau and the resulting Battle of Biscay (a misnomer since it was fought west of the Bay of Biscay, well inside the North Atlantic) had been a disaster for the Kriegsmarine; Alsterufer had failed to get out a distress signal and warn her would-be escorts before her sinking, and in turn the 8th and 4th flotillas had been mauled. In terms of warship losses, it was more devastating to the Germans than Sept-Îles had been for the British, albeit the loss of life was still greater at that battle, Charybdis‘ death toll alone exceeding the entire body count of the Biscay action. This did not mark the end of fighting in the Channel and Bay of Biscay however as there would be many more actions to follow. Franz Kohlauf for example, the victor at Les Triagoz and Sept-Îles and having survived the Biscay action, would later die in the action off Ile de Batz on 26 April 1944, which itself was followed by the action off Ile de Vierge just two days later. Not even including the wounded and ships damaged, those two actions alone resulted in the loss of German torpedo boats T27 and T29 and the Canadian destroyer HMCS Athabaskan along with the lives of hundreds of sailors.

Regardless, Clark’s victory and the overall success of Tunnel and Stonewall was still decisive as the Germans suspended all major blockade running operations, the exception being the “milk cow” cargo submarines trading valuable resources with Japan. While the Kriegsmarine would keep fighting until the end of the war, it would do so only as a tactical harassments force, especially after the loss of Tirpitz in November 1944. All major strategic goals of the Kriegsmarine had conclusively failed by the end of 1943, marked by both this defeat and also the Battle of the North Cape just two days earlier, where the Scharnhorst was sunk by a similar ambush in the Arctic.

Sources – :

  • The German Fleet at War 1939–1945, Vincent P. O’Hara
  • World War II at Sea: An Encyclopedia Volume 1, Spencer Tucker
  • German Destroyers of World War Two, M. J. Whitley

1 thought on “Operations Tunnel and Stonewall”

  1. The result of the Bay of Biscay battle was not a surprising outcome. The town-class light cruisers were to destroyers what battlecruisers were to regular cruisers. The only hope for the KM commander was to close the range with larger ships and he got shot up while doing it.

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