Naval Warfare
Outside
The Pacific
Convoy “HG76”.
The escorts strike back.
By
M. J. Bourne
Naval Warfare Outside the Pacific:
Convoy “HG76”
Copyright M J Bourne 1998
Published 1998 by
Vandering Publications
1 Lindal St,
Barrow-in-Furness
Cumbria
LA14 1AY
Reprinted 2010 by
Vandering Publications
29 Dumfries St,
Barrow-in-Furness
Cumbria
LA14 2DA
All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying or otherwise, without prior permission in writing from the copyright holder.
Background to the convoy war.
By the end of 1941 the struggle for control of the maritime trade routes was over two years old and going very much in favour of the Axis. The battle was vital. Britain was almost completely dependent on the steady flow of vital raw materials brought by merchant shipping. Without these supplies she could not make the weapons needed to prosecute the war, or even to feed her own population.
The Germans had several means at their disposal to attack the trade routes. Their powerful air force was an obvious tool for commerce warfare and soon made the English Channel too hot for British shipping, but the Luftwaffe was short of long-range aircraft and could have little effect on the Atlantic convoy system. Mines, spearheaded by the new magnetic types, were extensively sown at British harbours, but although individually dangerous their main effect was the tying up of resources to clear them.
In the 1930’s the German navy was still dominated by the “big gun ship” school, and planned to make extensive use of surface raiders to attack the British convoy system. As in most other navies, it too some time before they realised that battleships, although still powerful, were not the force they once were. They were expensive to build and maintain, and being large and visible there was a significant political cost if they were lost. In contrast submarines were cheap and quick to build, and less vulnerable owing to the difficulty in detecting them.
The main champion of the U-boat in the interwar years was Admiral Karl Donitz, himself an ex-submarine captain. U-boats had worked well for the Germans in 1914-1918, and Donitz realised that advances in technology that increased their reliability, speed, armament and range, could make them a war-winner in any future conflict. He supervised the clandestine construction of Nazi Germany’s new U-boat fleet, and was appointed in 1936. On the outbreak of war only a handful of U-boats were available, but early results were so good that a huge building program was initiated.
The British were far from complacent about the U-boat threat and in the interwar years had carefully thought out tactics and pioneered new methods of underwater detection. However, these new technologies were still very new indeed. Early radar and asdic (sonar) sets were notoriously delicate. Finding the elusive U-boats remained a problem.
The British had correctly instituted a convoy system as soon as war had broken out. Unfortunately in the early years they were critically short of escort vessels, especially ones with the range that could cover the vital transatlantic routes. Many of the early convoys were woefully ill-protected, and suffered horrific casualties as a result.
Against convoys Donitz developed the concept of the “wolf pack”. This involved a group of U-boats spreading out along the anticipated path of a convoy. The first to detect it would not attack itself but shadow, homing the other members of the pack by radio. The U-boats would slowly surround their prey and carry out a concerted attack, usually at night and on the surface. U-boats only normally submerged if they were threatened. This was because on the surface U-boats could use diesel engines, making them faster than merchant ships, but underwater they were forced to use electric motors, which made them slower than most convoys. During daylight they would withdraw to just over the horizon.
These tactics proved extremely effective. The small, deadly U-boats roved the sea lanes almost with impunity, and culled the barely protected merchant ships in vast numbers. Twelve hundred were lost in the first year of the war alone, the majority as a result of submarine attack.
In response the British stepped up escort production, and by 1941 over four hundred were in service. Nonetheless, an average of only two U-boats were being sunk every month. It was clear that mere numbers were not enough. New weapons were rushed into production, and training was intensified. Various convoy battles were analysed in detail, revealing amongst other things that depth charge patterns were frequently being set to explode at too shallow a depth. However, tactical thinking on how to defeat submarines was still primitive, and essentially defensive in nature.
Background to convoy “HG76”.
In the closing months of 1941 the focus of the convoy battles shifted from the mid-Atlantic to the shorter routes from Gibraltar to the British Isles. The move was occasioned partly by stronger escorts on the Atlantic routes but mostly by a decision by German High command to reinforce the Italians in the Mediterranean theatre. Donitz, who was convinced that his U-boats could decide the war in the Atlantic, considered this move to be a strategic error, but resigned himself to making the best of the situation. The shorter routes meant that his boats would be able to stay on patrol for longer, as they would be closer to their bases. They would also benefit from more air reconnaissance.
It did not take long for the British to pick up this shift of emphasis. Aircraft based at Gibraltar began reporting increased numbers of contacts with U-boats. The British responded by upgrading the escorts for the Gibraltar convoys—during the second week of December elements of the force that normally patrolled the Straits of Gibraltar reinforced the outward-bound convoy “OG77”. This convoy was spotted by the Germans, but arrived virtually unmolested. This convinced the British Admiralty that a heavy attack could be expected on the next Gibraltar convoy, “HG76”.
The primary covering force for “HG76” was the 36th escort group, commanded by the tempestuous but talented Commander F. J. Walker. It consisted of two sloops and seven corvettes. The convoy had been scheduled to sail in early December, but this departure was delayed while additional escorts were scraped up. Three more destroyers, two more sloops and three more corvettes were assigned from the Gibraltar patrol, although many would only be available for a short time. In addition, a hunting group of four more destroyers was deployed ahead of the convoy’s route. Most important of all the auxiliary aircraft carrier Audacity was made available.
Audacity had been part of the OG77 convoy and had proven to be very successful in suppressing German reconnaissance planes. She had been swiftly and basically converted from a German merchant ship, the Hanover, captured early in the war.Audacity was not a large or particularly suitable aircraft-carrying platform, and wastage of planes due to deck accidents was high. Originally allocated six small Martlet fighters, only four were available for the battle. It was intended to make up numbers with Swordfish torpedo-bombers from Gibraltar, but the sketchily converted ship proved incapable of handling them. However, Gibraltar based aircraft could still help to cover the convoy during the difficult time at the start of the voyage when it would be crossing the U-boat patrol line.
British Forces for convoy “HG76”.
36th Escort group (Walker)
Sloops
Deptford (Grimsby class)
Stork (Admiralty Yacht class) {Flagship}
&n
bsp; Corvettes
Convolvulus
Gardenia
Marigold
Pentstemon
Rhododendron
Samphire
Vetch (all Flower class)
The vital escort carrier Audacity, seen from a Gibraltar Swordfish.
Photograph courtesy of the Imperial War Museum, London.
Gibraltar Reinforcements
Aircraft-Carrier (Mackendrick)
Audacity (converted Hanover class)
No. 802 Squadron (part) with 4 x Martlets
Destroyers
Blankney (Hunt II class)
Exmoor (Hunt II class)
Hesperus (H class) {originally Brazilian}
Stanley (Town class) {ex USS McCalla}
Sloops
Black Swan (Black Swan class)
Fowey (Shoreham class)
Corvettes
Carnation (Flower class)
Jonquil (Flower class)
La Malouine (Flower class) {Free French}
Corvettes
Campion
Coltsfoot (both Flower class)
Merchant ships
32 in total, commanded by Commodore Fitzmaurice on Spero.
The convoy also included a merchant catapult ship, Darwin, and in fact “HG76” was one of the most heavily escorted convoys seen so far in World War II. There were so many escorts that Walker was able to deploy them in a double ring, making it even more difficult for U-boats to get at the valuable merchants. These last were arranged in the conventional rectangle, in a total of nine columns.
Commander Walker was an expert in anti-submarine warfare, and was to become the most successful and feared submarine hunters of the war, but this was to be his first chance to demonstrate his skills. He had studied the German tactic of "wolf-pack" attacks intensively and had come to the conclusion that existing tactics were far too defensive. From the beginning of the war it had been accepted that escorts should stay close to the merchants at all times. Walker resolved instead to counterattack detected U-boats immediately.
He devised a pre-arranged countermove codenamed "Buttercup". At the order "Buttercup port" (or starboard, astern, etc) the nearest escorts were to turn to the indicated direction on set courses, sweeping with asdic. All ships would illuminate the area with flares and special rockets known as "snowflake" (hardly an ideal solution, but one forced on the defenders by lack of reliable radar sets). The idea was to 'sanitise' a stretch of sea around a possible contact.
Unfortunately for Walker, the main reason why so many escorts were available was that the Gibraltar run was much shorter, and so older, low endurance escorts (of which there were a considerable number) could be used. These vessels were also slow, and therefore particularly unsuited for his tactic of aggressive responses to U-boat contacts.
The Germans were indeed planning a major attack on “HG76”. They were warned of its departure by agents in Spain, and Admiral Donitz ordered the Seerauber (pirate) wolf-pack to attack it. Unfortunately Seerauber was not as effective a fighting force as U-boat command would have wished. It was only seven boats strong and not all of them were in position even by the 15th of December. Most had been at sea for some time already and were not in peak fighting trim, having picked up a fair number of defects through action and weather damage. Worse, four of the boats were on their very first war cruises, with largely inexperienced captains and crews.
German naval forces (Grand Admiral Donitz).
“Seerauber” wolf-pack
U-boats
U-67 (Type IXC)
U-107 (Type IXB)
U-108 (Type IXB)
U-127 (Type IXC)
U-131 (Type IXC)
U-434 (Type VIIC)
U-574 (Type VIIC)
Brest reinforcements
U-boats
U-71 (Type VIIC)
U-567 (Type VIIC)
U-751 (Type VIIC)
Diverted from US east coast.
U-boat
U-125 (Type IXC)
Aircraft
FW-200’s of 1 KG-40 based at Bordeaux.
The convoy sets out.
It had been originally planned for “HG76” to sail on December 15th, but heavy congestion in Gibraltar harbour compelled it to set out on December 14th instead.
The first contact between the opposing sides came just before midnight that same day. A Gibraltar based Swordfish obtained a radar spot on a U-boat (U-67) six and a half miles off the starboard beam of the convoy and attacked from the stern. The submarine took evasive action to port and dived, and all three depth charges fell over the target.
At 0135 the same Swordfish located another U-boat (U-108) ten miles astern of the convoy. This also dived immediately, not knowing that the British plane had expended all of its depth charges. The Swordfish had no radio and it took some time for the contact to be reported to the convoy escort. Walker first learned of the attack via a message from the British Admiralty. Their direction finders had confirmed that a U-boat in the area had made a sighting report. In accordance with his new tactics, Walker immediately detailed Deptford and Rhododendron to search the area. No contact was made, and the two escorts abandoned the hunt at 0400.
Later in the night another Swordfish attacked a third U-boat with two depth charges, again with no result.
By daylight of December 15th “HG76” was beyond the operational radius of Gibraltar based Swordfish, and was reliant for air cover solely on Audacity's four Martlet planes. Patrols were duly sent out, but they failed to spot any U-boats. It seemed that the Germans had been given the slip. Walker and Commander Mackendrick of Audacity therefore agreed to suspend all anti-submarine air patrols for the time being. The flying hours of the fighters were limited and had to be conserved as much as possible. This was a gamble, and “HG76” turned out to be unlucky.
Although the U-boat patrol line had indeed failed to spot the convoy, the Germans had other resources. At 1848 on the evening of December 15th, whilst patrolling ten miles ahead of the convoy, Stanley reported a Focke-Wulf Condor reconnaissance aircraft circling outside of gun range. The fighters had already been stood down, and there was little the destroyer could do. Radio signals from the Condor alerted every U-boat in the wolf-pack and directed them to intercept courses. However U-127, moving hurriedly into position, had to run the gauntlet of the hunting group. She was spotted and sunk with all hands by the Australian destroyer Nestor, just off Cape St Vincent.
On the afternoon of December 16th the five smaller escorts from Gibraltar were detached back. Meanwhile the first U-boat had made contact. U-131 sent a sighting report and then settled down to shadow, surfacing at regular intervals to send in further reports. The first of these was very alarming for the submarine. Due to a hydrophone failure she came to periscope depth in the very middle of the convoy, but fortunately was not spotted! British direction finders did however pick up her signals and passed the information onto Walker. The response was swift. The following morning air patrols were reinstated and one duly spotted U-131 twenty-two miles off the convoy’s port beam. The three fastest of the escorts (Blankney, Exmoor and Stanley) were vectored into the attack. The corvette Penstemon, which happened to be closest at the time, also joined in, and it was her asdic that made the first contact with the submarine.
Penstemon dropped a depth charge pattern but then lost contact. She then joined the others in a line abreast formation and made a concerted search. The four British ships swept an area twelve miles to westward, and then turned south. U-131 was not in this search area, but had been badly damaged in Penstemon’s first attack. A lot of water had come in aft and into contact with the U-boat’s batteries, which began to release poisonous chlorine gas. Korvetten-Kapitan Baumann knew he would be forced to surface soon, and so went deep and attempted to put as much distance between himself and the escorts as possible.
His efforts were in vain. U-131 was only ten miles away when at 1247 she was finally forced to surface. She was instantly spotted and attac
ked. The U-boat valiantly fought back, shooting down one of Audacity's fighters that made a strafing run, but a single deck gun was no match for the concentrated firepower of the escorts. Baumann gave the order to abandon ship at 1330, and then scuttled his command. The action was watched by U-434 and U-574, which quietly slipped away.
The rest of the day passed uneventfully. British direction finders continued to report that the convoy was being shadowed. As soon as it was dark, the entire convoy made a sudden eighty degree turn to starboard in order to try and throw the Germans off the scent. However by now the U-boats were all around the convoy and were beginning to close in. U-434 made contact just after midnight, sent off a sighting report, and then settled down to shadow.
December 18th dawned bright and clear, the sea glassy calm. These weather conditions helped German reconnaissance aircraft to locate the convoy, but in every other regard worked to the advantage of the escorts. Good visibility made it difficult for U-boats to approach on the surface. U-434 was unwise enough to leave her withdrawal beyond the horizon just a little too late, and she was spotted by Stanley when only six miles off the port quarter of the convoy. On receipt of the destroyer’s warning the entire convoy altered course to directly north. Stanley then charged in to attack.
U-434 hurriedly dived and lined up on the approaching destroyer. She fired a single torpedo, which missed. That should have ended the affair, as Stanley's asdic had broken down. However, the submarine’s position was given away by a large oil slick. Stanley began to lay charges in the form of a square around the submarine, hoping to pin her in position.
Three sides of the square had been completed when Blankney came up to assist. She obtained both asdic and hydrophone contacts almost instantly and laid a snap six charge pattern on the violently swerving U-boat. Blankney then guided Stanley to lay a fourteen-strong pattern at deep setting, and then followed up with another spread of six charges of her own, this time at medium setting.
Convoy HG-76- the Escorts Strike Back Page 1