Battle of the Atlantic | World War II

Battle of the Atlantic | World War II


World War II's most extended continuous military engagement, the Battle of the Atlantic, lasted from 1939 until Nazi Germany was defeated in 1945, encompassing a significant portion of the war's naval history. From mid-1940 over the end of 1943, the campaign reached its pinnacle. The Battle of the Atlantic pitted German Kriegsmarine (Navy) U-boats and other warships and Luftwaffe (Air Force) aircraft against the Royal Navy, Royal Canadian Navy, United States Navy, and allied merchant vessels. Beginning 13 September 1941, their forces were supported by American ships and aircraft. After Germany's Axis partner Italy entered the war on 10 June 1940, the Germans were joined by submarines from the Italian Regia Marina (Royal Navy).

The United Kingdom was heavily reliant on imported commodities as a small island nation. The Combat of the Atlantic was essentially a tonnage battle. The Allies' war to resupply Britain and the Axis' attempt to halt the flow of merchant shipping allowed Britain to continue fighting. The fight resulted in a strategic triumph for the Allies since the German blockade was broken but at a high cost. In the Atlantic, 3,500 merchant ships and 175 warships were sunk, with 783 U-boats, the bulk of which were Type VII submarines, and 47 German surface warships, including the battleships Bismarck, Scharnhorst, Gneisenau, and Tirpitz, as well as nine cruisers, seven raiders, and 27 destroyers. Before the conflict, the Soviets destroyed 15 ships, and their crews scuttled 73 others for various reasons.

The War of the Atlantic has been described as the world's longest, largest, and most intricate naval battle. The campaign began shortly after the European War began, during the so-called "Phoney War," and lasted for more than five years, ending in May 1945 with the German surrender. By the end of 1942, the Allies had gained the upper hand, destroying German surface-raiders and defeating U-boats by mid-1943, but U-boat losses remained until the war's end.


First Aristocrat of the Admiralty A. V. Alexander requested "many more ships and vast numbers of men" from Parliament on 5 March 1941 to fight "the Battle of the Atlantic," which he equated to the Battle of France the previous summer. On 19 March, the Cabinet's "Battle of the Atlantic Committee" held its first meeting. The phrase "Battle of the Atlantic" was allegedly invented by Churchill shortly before Alexander's speech. However, there is considerable evidence of earlier use.


Following Germany's unrestricted submarine warfare during World War I, governments attempted to curb or eliminate submarines. The attempt was a flop. As an alternative, the London Naval Treaty required submarines to follow cruiser rules, which required them to surface, search, and place ship crews in a safe place (which lifeboats did not qualify for) before sinking them, unless the ship in question showed persistent refusal to stop or active resistance to visit or search, unless the boat in question showed stubborn refusal to stop or busy resistance to visit or search. These laws did not forbid merchantmen from being armed, but doing so, or requiring them to report contact with submarines (or raiders), rendered them de facto naval auxiliaries, removing the cruiser rules' protection. Submarine limits were effectively nullified as a result of this.

Early Skirmishes

In 1939, the Kriegsmarine needed the strength to compete for sea command with the united Royal Navy of the United Kingdom and the French Navy (Marine Nationale). When the war was declared, many German warships were already at sea, including most obtainable U-boats and the "pocket battlewagons" (Panzerschiffe) Deutschland and Admiral Graf Spee had sortied into the Atlantic in August. The small and short-range Type II U-boats, primarily used for minelaying and operations in British coastal seas, make up most of the 57 available U-boats. Destroyers, planes, and U-boats laid mines off British ports for much of the early German anti-shipping activity. The Royal Navy immediately established a convoy system to protect trade, which progressively spread beyond the British Isles, finally reaching Panama, Bombay, and Singapore. The convoy, Britain believed, would be a waste of ships that they couldn't afford to do because they could be needed in combat. Moreover, convoys permitted the Royal Navy to focus its escorts at the one spot where U-boats could always be found convoys.      

To patrol the commerce lanes in the Western Approaches and hunt for German U-boats, the Royal Navy organised anti-submarine hunting units based on aircraft carriers. This plan was fatally faulty since a U-small boat's silhouette allowed it to identify surface warships and submerge long before it was seen. The accompanying destroyers forced U-39 to surface and sink, making it the war's first U-boat loss. U-29 sank another carrier, HMS Courageous, three days later. For the first year of the war, escort destroyers hunting for U-boats remained a widespread but mistaken British anti-submarine policy. U-boats were almost always elusive, and convoys with no cover were put in far more danger.

German sinking success Günther Prien of U-47 exceeded Courageous a month later when he reached the British base at Scapa Flow and descended the ageing battleship HMS Royal Oak at anchor, becoming an instant hero in Germany. The tour of Admiral Graf Spee, which fell nine commerce ships of 50,000 GRT in the South Atlantic and the Indian Ocean throughout the first three months of the war, stretched British forces in the South Atlantic. The commander of the U-boat fleet, Admiral Karl Dönitz, had premeditated a maximum submarine exertion for the first month of the combat, with nearly all of the available U-boats patrolling in September. However, in the spring of 1940, Hitler's plans to invade Norway and Denmark led to the departure of most of the fleet's surface warships and ocean-going U-boats for fleet operations in Operation Weserübung.

The U-boats' primary weapon, the torpedo, had significant defects in the magnetic influence pistol (firing mechanism) due to the Norwegian battle. However, the shallow fjords limited U-boat manoeuvrability. The attentiveness of British warships, troopships, and supply ships offered the U-boats several opportunities to attack. The torpedoes burst early due to the influence pistol, hit and failed to explode due to a defective contact pistol, or ran beneath the target without exploding due to the influence feature or depth control not working correctly, and the ships sailed away uninjured. In more than 20 strikes, no British warship was sunk by a U-boat.

Submarine Warfare

Early in the war, Dönitz sent a note to the German Navy's Commander-in-Chief, Grand Admiral Erich Raeder, estimating that efficient submarine warfare could bring Britain to its knees due to its reliance on overseas trade. He pushed for a technique known as the Rudeltaktik, or "wolf pack," where U-boats would form a long line across the convoy's estimated path.  

This was in sharp contrast to the typical understanding of submarine deployment at the time, which saw the submarine as a lone ambusher waiting outside an enemy port to strike ships approaching and leaving. This was a highly successful method adopted by British submarines in the Baltic and the Bosporus during World War I, but it would be impossible to utilise if port approaches were well monitored. Experiments during the conflict had shown that the theory was flawed. Following Mahan's philosophy, the Japanese similarly believed in the concept of a fleet submarine and never utilised their submarines for close blockade or convoy interdiction.  

Before the war, the coastal patrol vessel, equipped with hydrophones and armed with a light cannon and depth charges, was the Royal Navy's principal anti-submarine weapon. During the 1920s and 1930s, the Royal Navy, like most others, had not considered anti-submarine warfare as a tactical subject. The London Naval Treaty prohibited unrestricted submarine warfare; however, the British ignored the fact that arming merchant ships, as Britain did from the start of the war, removed them from the protection of the "cruiser rules," and that anti-submarine trials with ASDIC had taken place in ideal conditions.

British Situation

The German conquest of Norway in April 1940, the swift capture of the Low Nations and the Italian in May and June, and France entrance into the combat on the Axis side in June all changed the fight at sea in three significant ways:

  • Only a few French ships joined the Free French Forces and fought against Germany. However, a few Canadian destroyers eventually joined them. As a result of Italy's declaration of war, Britain had to augment the Mediterranean Fleet and form a new Force H group at Gibraltar to replace the French fleet in the Western Mediterranean.  
  • The U-boats were able to get direct access to the Atlantic Ocean. This dramatically improved the situation for U-boats in the Atlantic, allowing them to target convoys further west and allowing them to patrol for more extended periods, effectively doubling the U-boat force's practical size. In addition, the Germans later constructed huge fortified concrete submarine pens for the U-boats in the French Atlantic bases, which were impervious to Allied bombing until mid-1944 when the Tallboy bomb became available. After completing their Atlantic missions, U-boats began returning to the new French bases in early July.  
  • Several older warships were pulled from convoy routes in April and May to support the Norwegian battle, then redirected to the English Channel to support the Dunkirk evacuation. Between May and July, seven destroyers were lost in the Norwegian campaign, six more in the Battle of Dunkirk, and ten more in the Channel and the North Sea, many of them to air attack due to a shortage of anti-aircraft weapons. Hundreds of others were harmed.

As a result, just as the number of U-boats on patrol in the Atlantic began to rise, so did the number of escorts available for convoys. The huge merchant fleets of conquered countries like Norway and the Netherlands fell under British control was the only comfort for the British. Following Germany's annexation of Denmark and Norway, the United Kingdom invaded Iceland and the Faroe Islands, creating bases and averting a German takeover.

Winston Churchill, who had taken office as Prime Minister on 10 May 1940, wrote to President Franklin D. Roosevelt on 10 May 1940, requesting the loan of fifty obsolete US Navy warships. This ultimately led to the "Destroyers for Bases Agreement," which functioned in exchange for 99-year tenancies on certain British bases in Bermuda, Newfoundland, and the West Indies, a monetarily beneficial bargain for the United States but a militarily beneficial bargain for Britain because it effectively freed up British military assets to return to Europe.

The Happy Time

Early U-boat operations from French bases were huge successes. Over 270 Allied ships were lost between June and October 1940, and U-boat crews dubbed "Happy Time." The U-boats' most significant issue was locating the convoys in the expanse of the ocean. The main convoy sightings were the U-boats due to persistent conflict between the Luftwaffe and the Kriegsmarine. As a result, the Germans could predict where and when convoys would arrive.

As a result, the British used operations research approaches to solve the problem and developed counter-intuitive strategies for defending groups. They realised that the part of a convoy grew by the square of its perimeter, implying that a convoy with the same number of ships and escorts was better protected than two convoys with the same number of vessels. Furthermore, because fewer large convoys could carry the same quantity of cargo, and huge convoys take longer to construct, decreasing frequency reduced the chances of detection. As a result, a few large convoys with a low escort ratio were safer than numerous small convoys with a more excellent escort to merchantman ratio.

Rather than assaulting Allied convoys individually, U-boats were ordered to work in wolf packs (Rudel) coordinated by radio. When one boat spotted a convoy, it would report it to U-boat headquarters, shadowing and reporting as needed until more ships arrived, which usually happened at night. Instead of dealing with solitary submarines, convoy escorts now had to deal with groups of up to six U-boats attacking simultaneously. Furthermore, corvettes were too sluggish to catch a U-boat that had surfaced.

Pack tactics were initially utilised to devastating effect in convoy clashes in September and October 1940. On 21 September, four U-boats attacked convoy HX 72, sinking eleven ships and damaging two others throughout two nights. In October, SC 7, a slow convoy escorted by two sloops and two corvettes, was overrun, losing 59 percent of its ships. Despite a robust escort of two destroyers, four corvettes, three trawlers, and a minesweeper, the German tactics were effective against the weak British anti-submarine methods, destroying a fourth of the convoy with no loss to the U-boats. Admiral Dönitz adopted the wolf pack as his primary tactic after the effectiveness of pack tactics against these convoys. In addition, the Admiralty was growing concerned about the number of ships sunk towards the end of 1940.

Italian Submarines in the Atlantic

Whereas this initial operation was a failure, with only 65343 GRT sunk amid August and December 1940, the situation gradually improved, and the 32 Italian submarines that operated there sank 109 ships totalling 593,864 tons for 17 submarines lost in return, giving them a subs-lost-to-tonnage-sunk ratio similar to Germany's in the same period, and higher overall. The Italians were equally effective in Gibraltar, where they used "human torpedo" chariots to disable many British ships.

Despite these victories, Dönitz did not approve of the Italian intervention, seeing the Italians as untrained and incapable of remaining calm in the face of the enemy. For example, they couldn't cooperate in wolf pack tactics or report contacts or weather conditions reliably. Thus their operations were moved away from the Germans'. Carlo Fecia di Cossato, leader of the submarine Enrico Tazzoli, and Gianfranco Gazzana-Priaroggia, commander of Archimede and afterwards Leonardo da Vinci, were among the more successful Italian submarine commanders who served in the Atlantic.


The integration of ASDIC with a plotting table and weaponry depth charges, and later Hedgehog, to create an anti-submarine warfare system, was a critical development. ASDIC provided a precise range and bearing to the target, but it was susceptible to thermoclines, currents or eddies, and schools of fish, necessitating the use of expert operators. As the attacker approached within 1,000 yards, the range and heading of the submarine would be plotted over time to estimate course and speed. The plan was to pass over the sub, firing depth charges from chutes at the stern at regular intervals, while throwers shot additional charges 40 yards to either side. To disable it correctly, a depth charge has to explode within 20 feet of a submarine. Because early ASDIC equipment had trouble measuring depth, adjusting the depth settings on different pattern parts was familiar.

The early iterations of this technology had some drawbacks. U-boats could dive much more profound than British or American submarines, exceeding 700 feet, much below the British depth charge maximum depth setting of 350 feet. More significantly, because early ASDIC sets couldn't see down, the operator lost contact with the U-boat during the attack's latter stages, when the submarine would almost surely be manoeuvring quickly. It allowed the U-boat to change positions without being detected.

Little was spent on anti-submarine ships or armaments due to the notion that ASDIC had addressed the submarine problem, the severe budgetary difficulties of the Great Depression, and the pressing demands for many other sorts of rearmament. Even more terrible was the situation at Royal Air Force Coastal Command. Patrol planes didn't have the range to cover the entire North Atlantic, so they could only machine-gun the place where they spotted a submarine dive.

Great Surface Raiders

U-boats were not considered the most severe threat to North Atlantic convoys considering their success. Nevertheless, a small but continuous stream of warships and armed commerce raiders set sail from Germany for the Atlantic beginning in 1940. The tragedy of convoy HX 84, which was attacked by the pocket battleship Admiral Scheer on 5 November 1940, illustrated the potency of a raider against a convoy. After the British discontinued North Atlantic convoys, the Home Fleet was dispatched to intercept Admiral Scheer. Admiral Hipper assaulted the troop convoy WS 5A on Christmas Day 1940 but was repelled by the accompanying cruisers. Admiral Hipper had better success two months later when she discovered the unaccompanied convoy SLS 64 of 19 ships and sunk seven of them on 12 February 1941.

The fearsome and speedy battleships Scharnhorst and Gneisenau, which outgunned any Allied ship that could catch them, set out from Germany in January 1941 for Operation Berlin, a strike on the commerce lanes. Because there were so many German raiders on the loose in the Atlantic, the British had no choice but to offer battleship escorts to as many convoys as possible. To assault convoys, the new battleship Bismarck and the cruiser Prinz Eugen set off. However, the loss of the Bismarck, the destruction of the network of supply ships that supported surface raiders, repeated air raid damage to the three ships, the entrance of the United States into the conflict, Arctic groups, and the perceived invasion threat to Norway had all convinced Hitler and the naval staff to withdraw.

Plan Z, Germany's naval expansion initiative, had come too soon. Battleships capable of destroying any convoy escort and escorts capable of annihilating the convoy were never developed. Even though the number of ships sunk by the raiders was tiny compared to the losses caused by U-boats, mines, and aircraft, their raids seriously interrupted the Allied convoy system, curtailed British imports, and put pressure on the Home Fleet.

Escort Groups

The creation of permanent escort units to increase the coordination and efficacy of ships and soldiers in battle was the most important. By 1941, public opinion in the United States had begun to turn against Germany. However, the war was still primarily fought between Great Britain and the Empire and Germany.

Initially, the new escort groups were two or three destroyers and a half-dozen corvettes. Under the harsh rule of Vice-Admiral Gilbert O., a new base was established at Tobermory in the Hebrides to train the new escort ships and their personnel for war demands. New short-wave radar sets capable of detecting surfaced U-boats and appropriate for small vessels and planes began to arrive in 1941 on a tactical level.

During the spring of 1941, the effects of these developments were first felt in the conflicts. First, the newly created 3rd Escort Group of four destroyers and two corvettes held off the U-boat pack in the combat of Convoy HX 112 two weeks later. Then, in early April, this new plan paid off when the group discovered Convoy SC 26 before its anti-submarine escort arrived.

The Field of Battle Widens

From 1939 till the defeat of Nazi Germany, the Battle of the Atlantic was the most extended continuous military engagement in World War II.

Growing American activity

The British decided in June 1941 to provide convoy protection for the whole North Atlantic passage. Commodore Leonard Murray, Royal Canadian Navy, acquired command of the Newfoundland Escort Force on 13 June 1941, under the overall management of the Commander-in-Chief, Western Approaches, at Liverpool. Six Canadian destroyers and 17 corvettes, backed up by seven Royal Navy destroyers, three sloops, and five corvettes, formed the force that escorted convoys from Canadian ports to Newfoundland and then to a rendezvous location south of Iceland, where the British escort units took over.

Despite its declared neutrality, the United States was increasingly involved in 1941. Following the United States' declaration of war, a Mid-Ocean Escort Force comprising British, Canadian, and American destroyers and corvettes was formed. The United States realised in June 1941 that the tropical Atlantic had become unsafe for unaccompanied American and British ships. As a result, the United States would have to either recall its ships from the ocean or enforce its right to unrestricted use of the seas in the future. Simultaneously, the British worked on technical advancements to counter Germany's submarine advantage.

Catapult Aircraft Merchantmen

Fitting ramps to the front of several cargo ships known as Catapult Aircraft Merchantmen, each armed with a single disposable Hurricane fighter aircraft, was used as a stop-gap measure. Nine combat launches were carried out, with eight Axis planes destroyed and one Allied pilot killed. Although the CAM ships and their Hurricanes did not achieve excellent results in terms of enemy aircraft shot down, the plane shot down were generally Fw 200 Condors that would frequently shadow the group out of range of the convoy's guns, reporting back the convoy's progression besides position so that U-boats could be directed on to it.

High-frequency Direction-finding

Ship-borne direction-finding radio equipment, known as HF/DF (high-frequency direction-finding, or Huff-Duff), began to be fitted aboard escorts in February 1942 and was one of the more significant developments. By the spring of 1943, these sets had become commonplace. HF/DF allows an operator to discern the direction of a radio broadcast without having to read the content.

An accompaniment may then run in the direction of the signal and fight the U-boat, or at the very least force it to dive, preventing an attack on the convoy. Escort ships, such as the USS Bogue, operating south of the Azores, using the bearing of an HF/DF signal to send aircraft down the bearing line to induce the submarine to immerse by bombarding and then attack with depth charges or a FIDO homing torpedo. The British also relied heavily on HF/DF stations to keep convoys informed of U-boat positions.

The radio technology underpinning direction finding was primary and well known by both sides. Still, before the conflict, the technique employed a manually rotating antenna to set the transmitter's direction. This was delicate work that required considerable time to do accurately. Moreover, because it only disclosed the line along which the transmission originated, a single set could not tell if the information was coming from the proper direction or its joint 180 degrees in the opposite direction.

Enigma Cipher

The way Dönitz ran the U-boat campaign necessitated a lot of radio traffic between the U-boats and the headquarters. Only Frank Birch, the chief of the German Naval Section, and Alan Turing, a mathematician, disagreed. In addition, the wiring of the unique naval Enigma rotors was needed by British codebreakers, and the demolition of U-33 by HMS Gleaner (J83) in February 1940 gave this knowledge.

The Royal Navy finished a intensive effort to help the codebreakers in early 1941, when crew members of the destroyer Bulldog boarded U-110 on 9 May and obtained her cryptologic information, including bigram tables and current Enigma keys. In addition, the familiarity codebreakers had with standard message content aided in the cracking of new keys.

Enigma intercepts paired with HF/DF enabled the British to plot the positions of U-boat patrol lines and guide convoys around them throughout the summer and autumn of 1941. As a result, in July 1941, merchant ship losses fell by more than two-thirds, and they stayed low until November. However, the increasing number of U-boats entering service countered this Allied advantage.

U-boat Captured by an Aircraft

On 27 August 1941, about 80 miles south of Iceland, a Coastal Command Hudson of 209 Squadron caught U-570 in an exceptional occurrence. When Squadron Leader J. Thompson spotted the U-boat on the surface, he dove straight for it and fired four depth charges as the submarine crashed to the bottom. Several crew members appeared on deck when the U-boat resurfaced, and Thompson fired his aircraft's cannons at them.

While under fire, the crewmen returned to the conning tower. A few minutes later, a white flag and a board with a similar colour scheme were displayed. Thompson radioed for help and circled the German ship. Until the advent of the armed trawler Kingston Agate under Lt Henry Owen L'Estrange, a Catalina from 209 Squadron took over observing the disabled U-boat. The U-boat was found beached in an Icelandic bay the next day. Even though no codes or secret papers were retrieved, the British now had a fully functional U-boat. U-570 was commissioned in the Royal Navy as HMS Graph after undergoing a refit.

Mediterranean Diversion

Hitler ordered Dönitz to bring U-boats into the Mediterranean in October 1941 to support German operations there. A series of clashes erupted around the Gibraltar and Sierra Leone convoys due to the resultant concentration near Gibraltar. Convoy HG 76 sailed in December 1941, escorted by Captain Frederic John Walker's 36th Escort Group, which consisted of two sloops and six corvettes and the first of the new escort carriers, HMS Audacity, and three destroyers from Gibraltar. The waiting U-boats quickly intercepted the convoy, resulting in a bloody encounter.

Walker was a tactical innovation, and the presence of an escort carrier meant that U-boats were regularly spotted and forced to dive before they could get near to the convoy. Despite the damage of Audacity after two days, Walker's squad sunk five U-boats in the next five days. Audacity, a destroyer, and just two commercial ships were lost by the British. The engagement marked the first time the Allies had won a convoy battle. Thanks to their tenacious efforts, the Allies gradually gained the upper hand until the end of 1941. Although Allied warships could not sink substantial U-boats, most convoys were utterly unaffected. The shipping losses were significant, but they were manageable.

Operation Drumbeat

The Japanese invasion on Pearl Harbor, followed by Germany's declaration of war on the United States, immediately impacted the campaign. At night, U-boats merely remained off the coast, scanning the horizon for ships silhouetted against the city lights. Admiral Ernest King, Commander-in-Chief U.S.A Fleet (Cominch), was initially opposed to the Royal Navy's request for a coastal blackout or convoy system because he loathed the British. King has been chastised for this move, but supporters note that the US destroyer fleet was inadequate (due to the transfer of 50 outdated destroyers to Britain earlier in the war). Moreover, protecting Allied army transports was considerably more vital than protecting merchant's vessels.

His ships were also battling the Japanese in the Pacific while transporting Lend-Lease equipment to the Soviet Union. The Army had legal control over all civil defence. The King could not order coastal blackouts because the Royal Navy (or Royal Canadian Navy) had advised that even unaccompanied convoys would be safer than merchants travelling alone. There were no troop shipments lost, but commerce ships travelling in US seas were exposed and suffered as a result. In 1943, the US launched almost 11 million tons of merchant's vessels; but, as the war progressed, the number of launches decreased as priorities shifted.

In May, King had finally gathered enough ships from Cominch and CNO to establish a convoy system. Shortly after, Le Tigre could track down the U-boat U-215 that had torpedoed the merchant ship, which HMS Veteran then sank; the U-boats' attention was turned back to the Atlantic convoys as a result of the enhanced coastal convoy escort system.

Battle Returns to the Mid-Atlantic

When the US eventually organised convoys, ship losses to the U-boats dropped dramatically, and Dönitz realised that his U-boats could be used elsewhere. The reoccurrence of the U-boats to the convoys from Canada to Britain was highlighted by Convoy SC 94. Hans-Rudolf Rösing was in charge of the headquarters.

There are still enough U-boats scattered throughout the Atlantic for many wolf packs to attack various convoy routes. Up to 15 boats would often strike in one or two waves, trailing convoys such as SC 104 and SC 107 during the day then attacking at night. The number of ships sunk in the "air gap" between Greenland and Iceland soon rose, and by October 1942, 56 vessels weighing over 258,000 tonnes had been lost.

The number of U-boats lost increased as well. Horton used the increasing number of escorts available to form "support groups" to help convoys under attack. Unlike conventional escort groups, support units were not directly responsible for the protection of any convoy. Whereas ordinary escorts would have to split up and stay with their convoy, the support group ships might continue hunting for a U-boat for several hours.

Ahead-Throwing Weapons

The depth charge was a vessel's only weapon for destroying a submerged submarine at the start of World War II. The deep charges had to sink to the depth where they were supposed to explode. The depth charges then left a disrupted water region, making it harder to reestablish ASDIC/Sonar communication. One of the remedies devised by the Royal Navy in response to this difficulty was the ahead-throwing anti-submarine weapon, the first of which was Hedgehog.

Hedgehog was a multi-spigot mortar that launched contact-fused bombs ahead of the firing ship while the target remained within the ASDIC beam. Because the cruiser did not have to clear the area of bursting depth charges to avoid damage, it could approach slowly, making its position less visible to the submarine commander.

Leigh Light

U-boat activity could be suppressed across a large region if radar-equipped aircraft detected them, but an aircraft strike would require good visibility. Because of two factors, U-boats were largely safe from aeroplanes at night: 1) Radar at the time was incapable of detecting them at distances of less than one mile; On 5 July 1942, U-502 was the first verified kill utilising this technology.

The Leigh light allowed the British to attack enemy submarines on the surface at night, forcing German and Italian commanders to stay below the surface, especially when approaching sub bases in the Bay of Biscay. Because planes could not be seen at night and the roar of an incoming aircraft was inaudible above the din of the submarine's engines, U-boat commanders who survived such attacks noted a tremendous fear of this weapon system.

Metox Receiver

This allowed U-boats to elude detection by Canadian escorts armed with antiquated radar sets and follow convoys where these sets were in service. It did, however, present problems for the Germans since it occasionally detected stray radar transmissions from distant ships or planes, leading U-boats to submerge when they were not in danger and preventing them from recharging batteries or utilising their surfacing speed. Metox gave the commander of the U-boat an advantage that the British had not foreseen.

Germans break Admiralty Codes

This allowed U-boats to elude detection by Canadian escorts armed with antiquated radar sets and follow convoys where these sets were in service. It did, however, present problems for the Germans since it occasionally detected stray radar transmissions from distant ships or planes, leading U-boats to submerge when they were not in danger and preventing them from recharging batteries or utilising their surfacing speed. Metox gave the commander of the U-boat an advantage that the British had not foreseen.

Enigma in 1942

The Kriegsmarine transferred the U-boats to a new Enigma network (TRITON) on 1 February 1942, which utilised the new four-rotor Enigma machines. The Allies had no idea where the U-boat patrol lines were since codebreakers could not read this new key. This made avoiding contact much more complex, and the wolf packs devastated several convoys as a result. This condition lasted ten months. The Allies had to rely on HF/DF fixes and decryptions of Kriegsmarine signals encoded on previous Enigma machines to learn about submarine movements. Alerts from coastal troops about U-boat arrivals and departures at their bases in France, as well as reports from the U-boat training command, were among the messages. Commander Rodger Winn's Admiralty Submarine Tracking Room provided their best estimations of submarine movements based on these clues but insufficient information.

Then, as the German submarine U-559 foundered off the coast of Port Said on 30 October, crew members from HMS Petard retrieved Enigma documents. The codebreakers were able to break TRITON due to this, an achievement credited to Alan Turing. By December 1942, Enigma decrypts had revealed U-boat patrol positions once more, and shipping losses had dropped substantially.

German Command Centre

After the St Nazaire Raid on 28 March 1942, Raeder decided that the risk of another seaborne attack was too significant, so he moved the western expertise centre for U-boats to the Château de Pignerolle. There was a command shelter was constructed and from which all Enigma radio messages between German command and Atlantic-based operational U-boats were transmitted/received. Hans-Rudolf Rösing was named FdU West in July 1942. Pignerolle became his base of operations.

The Climax of the Campaign

Winter weather brought a temporary break from the combat in January before convoys SC 118 and ON 166 arrived in February 1943, but convoy clashes resumed with the same vigour in the spring. Because there were so many U-boats patrolling the North Atlantic, convoys found it difficult to avoid detection, resulting in a series of bloody confrontations.

The Germans improved the U-boat Enigma key on 10 March 1943, blinding the Allied codebreakers at Bletchley Park for nine days. Convoys SC 121, UGS 6, HX 228, SC 122, and HX 229 fought in conflicts that month. SC 130 saw at least three U-boats sunk and one U-boat damaged for no losses two weeks later. In the face of disaster, Dönitz halted operations in the North Atlantic, declaring, "We had lost the Atlantic Battle." Nevertheless, 43 U-boats were sunk in May, with 34 in the Atlantic.

Convergence of Technologies

Arnold will dispatch a squadron of ASW-equipped B-24 bombers to Newfoundland to bolster the air escort of North Atlantic convoys. General Arnold instructed his squadron leader to only conduct "offensive" search and attack missions rather than convoy escorts. In July 1943, an agreement was made, and the trade was finalised September 1943.

The emergence of merchant aircraft carriers (MAC ships) and the expanding number of American-built escort carriers gave additional air cover. They sailed with the convoys and supplied much-needed air support and patrols across the Atlantic, flying Grumman F4F Wildcats and Grumman TBF Avengers.

As a result of American construction programs and the release of escorts committed to the North African operations in November and December 1942, many escorts became available. Finally, enough guards would secure convoys and form hunter-killer groups typically centred on escort carriers to hunt U-boats aggressively.

The British had developed an efficient sea-scanning radar small enough to be carried in patrol planes armed with airborne depth charges by spring 1943. As a result, in the last three years of the war, RAF Coastal Command sank more U-boats than any other Allied service. However, U-boat losses were 258 in 1943 due to various causes.

South Atlantic

These were implemented in the second half of 1941 after negotiations with Brazilian Foreign Minister Osvaldo Aranha on behalf of Dictator Getlio Vargas. Submarine raids by Germany and Italy were then extended to encompass Brazilian ships wherever they were, and from April 1942, they were discovered in Brazilian waters. Although the first Brazilian attack against the Italian submarine Barbarigo was carried out by Brazilian Air Force planes on 22 May 1942, it was unsuccessful. Finally, following a series of U-507 attacks on commerce vessels off the coast of Brazil, Brazil formally entered the war on 22 August 1942, bolstering the Allied strategic position in the South Atlantic.

Despite its tiny size, the Brazilian Navy had sophisticated minelayers capable of escorting coastal convoys and aircraft that required only minor modifications to become competent for maritime patrol. Brazil guarded 3,167 ships in 614 convoys totalling 16,500,000 tons during its three-year war, mainly in the Caribbean and South Atlantic, alone and with the US, with losses of 0.1 percent. Three of Brazil's warships were sunk, with 486 men killed in combat, including 332 Bahia cruisers.

Final Years

While waiting for the next generation of U-boats, the Walter and Elektroboot types, Germany undertook many attempts to modernise its U-boat force. However, the loss ratio was disastrous, with eight ships of 56,000 tons and six battleships sunk for the loss of 39 U-boats. The Luftwaffe also familiarized the long-range He 177 bomber and the Henschel Hs 293 guided glide bomb, which took a lot of lives but were not a significant danger because of Allied air superiority.

German Tactical and Technical Changes

To counter Associated airpower, UbW increased anti-aircraft weapons on U-boats and created specially-equipped "flak boats," which were designed to stay on the surface and fight attacking planes rather than diving and dodging. While assaulting pilots frequently called in surface ships if they encountered too much opposition, orbiting out of range of the U-guns boat's to maintain contact, a U-boat that remained uncovered increased the chance of its pressure hull being punctured, rendering it unable to submerge. The Germans used Bold canisters, dubbed Submarine Bubble Target by the British, to generate false echoes and Sieglinde self-propelled decoys to mislead Allied sonar.

The pattern-running Flächen-Absuch-Torpedo (FAT) ran a pre-programmed track crisscrossing the convoy pathway, and the G7es acoustic torpedo, known to the Associates as German Naval Acoustic Torpedo, GNAT, which homed on the propeller noise of a target, both boosted torpedo development. Initially, this was quite effective, but the Allies swiftly developed tactical and technical countermeasures. Unfortunately, none of the German countermeasures was genuinely compelling. By 1943, Allied air strength had grown to the point that U-boats were being targeted immediately after leaving port in the Bay of Biscay.

Last Actions

The Germans debuted the Elektroboot late in the war, with the Type XXI and short-range Type XXIII. The Type XXI could travel at 17 knots submerged, faster than Type VII surfaced at full speed and faster than Allied corvettes. However, only one Type XXI and five Type XXIII boats were operational by 1945. In the first five months of 1945, the Type XXIIIs conducted nine patrols, sinking five ships; by contrast, Type XXI conducted only one combat patrol before the war ended, making no contact with the enemy.

Over 200 boats were scuttled to evade capture as the Allied armies drew in on the U-boat sites in North Germany; twenty-three ships were sunk in the Baltic while trying this route in the first week of May. The last engagements in American waters occurred on May 5–6, 1945, when the steamship Black Point was sunk, and U-853 and U-881 were destroyed in separate events. Finally, on May 7–8, the Battle of the Atlantic came to a close.


The Germans could not halt the flow of strategic supplies to the United Kingdom. As a result of this failure, men and supplies for the D-Day landings were built up. The defeat of the U-boat was a critical prelude to the Allied troops and supplies being gathered to assure Germany's defeat. However, victory came at a high price: between 1939 and 1945, 3,500 Allied commerce ships totalling 14.5 million gross tons, 175 Allied warships, and 72,200 Allied naval and merchant seamen perished.

The large bulk of Allied warships lost in the Atlantic and near coasts were small warships of 1,000 tons or less, such as frigates, destroyer escorts, sloops, submarine chasers, or corvettes. Still, there were also losses of one battlecruiser (Hood), one battleship (Royal Oak), three escort carriers (Dasher, Audacity, and Nabob) (Curlew, Curacoa, Dunedin, Edinburgh, Charybdis, Trinidad, and Effingham), two aircraft carriers (Glorious and Courageous),. The Germans lost 783 U-boats and 30,000 sailors, accounting for three-quarters of the 40,000-man U-boat fleet. Germany's surface force suffered enormous losses, with four battleships, nine cruisers, seven raiders, and 27 destroyers sunk.

Merchant Navy

United Kingdom

During WWII, British merchant ships accounted for approximately a third of all commerce shipping worldwide. The crewmen were given an 'MN' lapel emblem to show that they were serving in the Merchant Navy to counter this. The British merchant navy was made up of ships from various private shipping lines, such as the British Tanker Company's tankers and Ellerman and Silver Lines' freighters. In addition, during the war, the British government had new ships built by the Ministry of War Transport (MoWT), which were known as Empire ships.

United States

In addition to its existing commerce fleet, US shipyards constructed 2,710 Liberty ships totalling 38.5 million tons, much exceeding the 14 million tons of cargo sunk by German U-boats during the war.


More than 70 cargo vessels from Canada were lost. A total of 1,600 merchant sailors, including eight women, were slain. Canada conscripted all of its commercial vessels two weeks before declaring war. The Royal Canadian Navy took control of all shipping on 26 August 1939, based on information gathered by British agents regarding German shipping movements.

Canada had 38 ocean-going merchant vessels at the start of the conflict. When on leave, ordinary seamen were given an 'MN Canada' badge on their lapel to show their service. "Any Navy or Air Force did not fight the Battle of the Atlantic. It was won by the heroism, endurance, and tenacity of the British and Allied Merchant Navy," Rear Admiral Leonard Murray, said at the end of the war.


Norway's Merchant Navy was the fourth largest globally before the war, and its ships were among the most advanced. Vidkun Quisling, the Norwegian Nazi puppet leader, ordered all Norwegian vessels to sail to German, Italian, or neutral ports. The Norwegian Merchant Navy's ships were handed over to the government-run Nortraship, offices in London and New York. The Allies relied heavily on Nortraship's contemporary ships, particularly its tankers.


This was because most ships sunk by U-boats were not in convoys and were sailing alone or had become isolated from convoys. As a result, supply routes to Britain were never disrupted during the campaign. To win, the U-boat arm needed to sink 300,000 GRT each month to overwhelm Britain's shipbuilding capabilities and weaken the merchant marine.

Germany barely met this goal four times in the first 27 months of the war, but after December 1941, when the US merchant fleet and shipyards joined Britain, the target was virtually quadrupled. The 700,000-ton target was met in just one month, November 1942, and average sinkings fell to less than one-tenth of that level by May 1943. Even though the U-boat arm sunk 6,000 ships totalling 21 million GRT by the end of the war, the Allies had built almost 38 million tons of new shipping.

The explanation for the erroneous belief that the German blockade was on the verge of succeeding may be found in postwar memoirs by both German and British authors. Blair blames the distortion on propagandists who exaggerated and praised German submarine victories, while allied authors, he says, had their reasons for exciting the danger.

According to Dan van der Vat, unlike the United States, Canada, and the rest of Britain's dominions, which were all protected by maritime distances, Britain was at the end of the transatlantic supply route closest to German bases prompted Churchill's concerns. In March 1943, it was combined with a series of big convoy fights in the space of a month, undermining trust in the convoy system to the point where Britain pondered abandoning it, even though the U-boat had previously been effectively defeated.

Shipping and U-Boat Sinking's Each Month

This would result in a reduction of 40% to 53%. According to a postwar account published for the British Admiralty based on German records by a former U-boat commander and Dönitz's son-in-law, multiple extensive studies into whether their operations were compromised by cracked code proved negative, and they were defeated.

The data is colour-coded to split the fight into three epochs: before the Enigma code was broken after it was broken, and with the introduction of centimetric radar, which could detect periscopes and expose submarine conning towers above the water's surface. Although more U-boats were sunk, the number of U-boats in service had more than tripled. Moreover, shipping losses decreased after the new radar was put into use, reaching a substantially lower level than in the early months of the conflict.

Last updated: 2022-January-09
Tags: History World War II
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