Winning the Battle of the Atlantic: 1943

By Zoë C. Vince

This article aims to explore the various contributing factors to Allied successes in March to May of 1943.  Although the Atlantic continued to be a major theatre of operations until the end of the Second World War, it may be argued that the threat posed by German U-Boats had been greatly diminished by Allied efforts in the spring of 1943.

This author will argue that despite a variety of elements of the anti U-boat war, from intelligence to technology, combining to facilitate the withdrawal of U-boats from the North Atlantic in May 1943, it was in particular the developments in training and organisation of the Allied convoy system which can be most directly linked to German failures in this period.


The successful application of Allied tactical and technological advancements to anti-submarine warfare, culminating in the spring of 1943, lead to a turning point in the Battle of the Atlantic.  Combating the U-boat threat required close co-operation between the Allies, integrated inter-service training and command, and co-ordination of tactics, procedures and technologies.  Although there are a number of factors which contributed to Dönitz’s withdrawal of the U-boats in May 1943, it was the organisation of the convoys, support and escort groups by Admiral Sir Max Horton, and the training of crews specifically in anti-submarine warfare which provided the cohesion and professionalism required to both prevent U-boats sinking ships in convoy and simultaneously destroy a comparatively high number of submarines.  The superior standard of efficiency achieved by the Allies, in all aspects of the anti-submarine battle, ensured that the German U-boats ceased to pose a serious threat in the Atlantic.  It is clear, therefore, that training and organisation was an extremely important factor.

While addressing this subject, it would be impossible to list and discuss Allied training and organisational developments in isolation without acknowledging closely related elements of the anti-submarine campaign such as technology, signals intelligence and air power.  This article will seek to argue that while these complementary factors contributed to the Battle of the Atlantic to varying degrees, it was the improvements in training and organisation of the convoy system which enabled the effective co-ordination and optimum usage of all related developments.

The Atlantic theatre of naval operations remained important throughout the war, indeed a contemporary naval officer stated that without Allied success in this theatre “the grand conception for the liberation of Europe might never have materialised”.  Among historians there is a consensus that May 1943 marked a turning point in the Battle of the Atlantic.  Earlier historiography including the British and US naval histories described a crisis occurring in March 1943, with communications from the old world to the new coming under severe threat, followed by the sudden and unexpected collapse in May of the U-boat campaign.  Revisionist research into this subject, while acknowledging the importance of May 1943 as a pivotal month in the Battle of the Atlantic, has generally disputed the traditional view of crisis, stressing that while certain Allied convoys suffered great losses in March and April many others suffered none.  Referring to Admiralty reports, Duncan Redford states that only thirty one per cent of all ocean convoys were attacked in March, furthermore between August 1942 and May 1943 there were eight months in which the Allies suffered higher percentage losses than March.  This indicates, rather than the ‘sudden collapse’ of the U-boat war in May, a more gradual development with successful practical application of improved Allied anti-submarine tactics and technologies.  Similar revisionist research also focuses on the absence of German optimism in this period of supposed Allied crisis, consulting statistics which clearly show an increase in non-productive U-boat patrols between January and April 1943, and stating that as early as February Dönitz had reported to Hitler that the North Atlantic run campaign was not succeeding.

This reversal in fortunes can be attributed to a number of different developments which ran parallel with the progression of training and organisation. Improvements in technology in particular played an essential role in both Allied and Axis naval operations, with both sides seeking to improve on the other’s advancements.  One example of this was the German capture in 1942 of a long range Vickers Wellington bomber fitted with Air to Surface Vessel (ASV) Mark II airborne radar, and the subsequent German invention of a listening receiver as a countermeasure to ASV.  There were also improvements made to the means of engaging U-boats i.e. weapons such as the ‘hedgehog’ mortar or the improved Air Ministry and Admiralty depth charges.  It may be argued, however, that the more influential development was that of radar and direction finder technology, aimed at locating U-boats.

An example of ‘Huff-Duff’ equipment.

By its nature, the submarine was “a weapon of position and surprise”, and so the ability to locate U-boats through the use of High Frequency Definition Finders (HF/DF) and 10cm airborne radar (ASV Mark III), both fitted in the first few months of 1943, effectively removed the element of surprise and severely hindered U-boat operations.  Burns supports this by citing Dönitz in a report to Hitler, writing in May 1943 that “the enemy, by means of location devices, makes fighting impossible”.

‘Bombes’ like these were used to simulate the action of the German Enigma rotors.

In addition to technology, any discussion of the training and organisation of anti-submarine warfare in the Battle of the Atlantic also requires acknowledgement of the work carried out by British signals intelligence at Bletchley Park in breaking the German Enigma cipher.  Post-war historians had claimed that the cryptographers at the Government Code and Cypher School (GC&CS) had shortened the war and that breaking the Enigma had been a huge success.  More recently however, Ferris has denounced the tendency for historians to over-emphasise the role of signals intelligence, stressing that while its contribution was ‘notable’, the correlation between GC&CS’ successes and the overall Allied seizure of initiative in late 1942 was complementary rather than causal.  With this in mind, although on the thirteenth of December 1942 GC&CS had broken the ‘Shark’ Enigma through the use of a four-rotor electronic ‘Bombe’, complete understanding and rapid deciphering of German signals was not fully achieved until August 1943, after the U-boats had been withdrawn.  In addition by February 1943 B-Dienst, German signals intelligence, had broken the British Naval Cypher No. 3 used for convoys, providing Dönitz with a “presen[ce] in British operations rooms”.  With both combatants therefore by 1943 possessing intelligence on the other’s routes and positions, and with direction-finding technology allowing clearer location of enemy vessels, it may be argued that signals intelligence in comparison played an important, but not crucial role in May 1943.

Training and organisation in contrast was integral to the growing successes of the escort and support groups, with several different elements combining to optimise anti-U-boat operations.  Operational Research scientists under Professor Blackett contributed to the Battle of the Atlantic by engendering a “revolution in organization”; their findings contributing to Horton’s re-organisation of the anti-submarine effort through scientific calculation and research.  From 1941 onward, Blackett and his staff applied scientific findings to naval operations, helping to devise theatre-level stratagems and also solve problems such as the optimum allocation of resources to the production of merchant shipping vis-á-vis anti-submarine escorts.  Arguably Operational Research’s most influential breakthrough, however, was the analysis of shipping losses in relation to convoy size.  This investigation, carried out during 1941 and 1942, concluded that the number of losses was independent of the size of the convoys, with larger convoys being attacked by ‘wolfpacks’ no more often than smaller ones.  It was calculated that by increasing the size of individual convoys and thereby reducing the number of convoys open to attack at any one time, there could be a reduction in losses of up to 56 per cent.  As well as achieving reduced losses, the decision taken to increase convoy size had the secondary effect of freeing up escorts for more proactive work as part of the new support groups, greatly aiding the offensive campaign.

As a result Operational Research contributed greatly to Horton’s organisational reforms of Western Approaches Command and to the way the anti-submarine campaign was conducted.  Operational Research’s findings have been dubbed “quantitative common sense”, however their collation and analysis lead to measurable successes.  The incorporation of civilian scientists so closely into high level naval command structures, reporting directly to the Vice-Chief of the Naval Staff at the Admiralty, demonstrated flexibility and innovation at the highest levels, features notably absent in the German counterpart.

The establishment of support groups marked the progression of the Allied anti-U-boat campaign from defensive to offensive actions.  The average support group comprised destroyers, sloops and frigates, which were faster and had greater range than the corvettes widely used earlier in the war.  The United States’ naval operations historian Samuel Morison recognised Horton’s reorganisation of available resources as a “tactical innovation”, highlighting the ability of the support groups to aid ‘harassed’ convoys at short notice and thus alter the outcome of many such engagements.    Availability of escort destroyers and aircraft carriers and allocation of resources to the North Atlantic had previously been a large problem, delaying the formation of support groups until March 1943 and preventing adequate defence of convoys passing through the mid-Atlantic ‘Black Gap’.  During mid to late April, in contrast, an example of the Admiralty’s Operational Intelligence Centre’s reports stated that “support groups have been invaluable this week and skilful handling has produced them in the right place at the moment when they are needed”.

Inter-service co-operation was crucial to success in the Atlantic

Airpower too was to play a vital role in convoy defence, and therefore availability was crucial.  The United States’ Navy was undergoing changes in organisation itself with regard to inter-service co-operation with the Army Air Force, but by the end of 1942 it was able to send two squadrons of very-long-range (VLR) B-24 Liberator heavy bombers to aid RAF Coastal Command.

One of the first Allied aircraft carriers used in escort groups: HMS Biter.

The development of different types of aircraft carriers had also been delayed by production problems and their allocation to the North Atlantic postponed due to the prioritisation of other operations, namely ‘Husky’ and ‘Torch’, but the first escort carriers HMS Biter and USS Bogue joined support groups between March and May 1943.  Redford emphasises the reluctance of both the US and British command to divert bombers away from the strategic bombing offensive, however the eventual allocation of air power to Coastal Command support groups especially alongside the newly arrived aircraft carriers was hugely successful.  A study carried out in the summer of 1943, centred on the successes of support groups in May 1943, found that their use in operations raised the number of U-boat ‘kills’ by 45 per cent, with most U-boats being sunk in close proximity to convoys.  In summary it may be argued that rather than as an isolated arm, the contribution of air power to anti-submarine operations was most successful when employed as part of support groups, coordinating with surface vessels.

It is clear that superior organisation of shipping and available aircraft was the key to effectively combating the U-boat threat through the co-ordination of available technology, intelligence and resources, but it was the intensive training and valuable experience of the anti-submarine escort and support groups which optimised efficiency and contributed to improved success rates.  Chalmers claimed “whatever the weapon and whatever the counter, training was the keystone of Horton’s regime”.

The Western Approaches Tactical Unit, Liverpool.

Horton ‘inherited’ the Western Approaches Tactical Unit (WATU) in November 1942 which gave synthetic training to escort captains and group commanders in the tactics of convoy battles.  In January 1943 Horton added practical ship-based training on HMS Philante, based at Larne in Northern Ireland, complete with training submarines.  Horton’s emphasis on training was also shown by his decision to increase time in harbour for individual crews for the purpose of intensive training.  By the end of the war, over 5,000 officers had completed a 6-day course in anti-U-boat tactics at WATU.  The diaries of A.F.C. Layard, although not directly applicable to the pre-May 1943 period, provide a favourable first-hand account of Horton’s training programme, Whitby commenting that “one of the great lessons of the Battle of the Atlantic was the importance of continual group training”.  This focus on training was not restricted to escort groups, with improved co-operation between the Royal Navy and RAF at Derby House allowing combined training exercises leading in turn to the adoption of the same signal codes and synchronised navigation, thus optimising the support groups’ effectiveness.  Improved defence of ships in convoy was the key to overcoming the U-boat threat.  The establishment and training of support groups therefore clearly aided the anti-submarine effort far more than any single technological invention or intelligence breakthrough.

To conclude, the organisation of convoy size and structure, the introduction of support groups and Horton’s insistence on widespread, practical training had resulted in a greatly improved and efficient convoy defence system.  By April 1943, Syrett claims, the Allies were fighting and beginning to defeat the Germans with the tools of “aircraft and electronic warfare”.  The word ‘tools’ here is significant.  It is clear that HF/DF, 10cm radar and the ‘hedgehog’, as well as the signals intelligence breakthroughs and aircraft support facilitated greater successes in the location of and engagement with U-boats.  Despite this, it is unlikely that these tools could have been used to optimum effect without the proper experience, training and synchronisation of all elements of the anti-submarine battle.  The development of the support groups represented the transformation of operations from broadly defensive to offensive, and therefore it could also be suggested that Horton’s support groups personified, so to speak, the turning point of the Battle of the Atlantic.  The training and organisation of the convoy system was the key to optimising all other advances made, and therefore was hugely important to Allied success in the Atlantic.

The author may be contacted on Twitter @zcvince


3 comments on “Winning the Battle of the Atlantic: 1943

  1. Zoe,

    An interesting piece. My only comment is that it is worth stressing the change in organisational culture within both the RAF and RN, and their williingness to work together. This is especially important concerning the decision to place Coastal Command under the operational direction of the RN. This was a tough decision for the Air Ministry as it went against their one key belief; the independence of air power. However, they did it. This type of change did not come easily but that fact that it did is one of the cornerstones of allied vistory in the Atlantic. On the other hand it is one of the reasons the Germans do so badly i.e. the Kreigsmarine and Luftwaffe very rarely talked to each other!

    On the bomber issue. I would be careful with Redford’s analysis. He hold the typical view of some naval historians with regards to where Bomber Command should have been used. However, it is quite a narrow viewpoint that ignores larger strategic considerations. Just to get a flavour of what, and who he write for, go an have a look at the Phoenix Think Tank website.

  2. Thanks Ross,
    All points gladly received. I agree wholeheartedly with your comment on the German failure to effectively communicate and coordinate between services, insufficient German air power in this theatre no doubt contributed hugely to Allied successes. It is also interesting looking into the US-UK dialogue regarding allocation of air power to the Atlantic with the US understandably looking toward the Pacific, and Coastal Command (as far as I understand it) being viewed rather as the poorer relation to Bomber Command. Despite the initial scarcity of resources, increased co-operation, awareness and training among RAF and RN units, and as you have mentioned the change in organisational culture, together greatly aided the anti U-boat effort. In my opinion the best example of RN-RAF co-operation in this period was the integration of RAF Coastal Command training as part of the Combined Service Anti-Submarine Training Unit, set up in April 1943. You are of course right, the role of Air Power should not be marginalised, but in my opinion it was the transformation of training and organisation, including that of RAF Coastal Command, which explains the reversal in Allied fortunes in 1943. Your point about Redford is also welcome, will look into the Phoenix Think Tank.

  3. Zoe,

    Great article, thanks. What do you think were the enduring lessons we’ve learned from the battle of the Atlantic, particularly of the integration between the RAF and Navy?

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