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Battle of the Atlantic | HearLore
Battle of the Atlantic
The Battle of the Atlantic was the longest continuous military campaign in World War II, stretching from 1939 to the defeat of Nazi Germany in 1945. At its core was a desperate struggle for survival, as the United Kingdom, an island nation, required more than a million tons of imported material per week to survive and fight. Without these supplies, the British war effort would collapse, and the nation would be forced to surrender. The campaign pitted U-boats and other warships of the German navy and aircraft of the air force against the Royal Navy, Royal Canadian Navy, United States Navy, and Allied merchant shipping. Convoys, coming mainly from North America and predominantly going to the United Kingdom and the Soviet Union, were protected for the most part by the British and Canadian navies and air forces. These forces were aided by ships and aircraft of the United States beginning on the 13th of September 1941. The Germans were joined by submarines of the Italian royal navy after Germany's Axis ally Italy entered the war on the 10th of June 1940. As an island country, the United Kingdom was highly dependent on imported goods. Britain required more than a million tons of imported material per week in order to survive and fight. The Battle of the Atlantic involved a tonnage war: the Allies struggled to supply Britain while the Axis targeted merchant shipping critical to the British war effort. Rationing in the United Kingdom was also used with the aim of reducing demand, by reducing wastage and increasing domestic production and equality of distribution. From 1942 onwards, the Axis also sought to prevent the build-up of Allied supplies and equipment in the UK in preparation for the invasion of occupied Europe. The defeat of the U-boat threat was a prerequisite for pushing back the Axis in western Europe. The outcome of the battle was a strategic victory for the Allies, the German tonnage war failed, but at great cost: 3,500 merchant ships and 175 warships were sunk in the Atlantic for the loss of 783 U-boats and 47 German surface warships, including 4 battleships, 9 cruisers, 7 raiders, and 27 destroyers. This front was the main consumer of the German war effort: Germany spent more money to produce naval vessels than every type of ground vehicle combined, including tanks. The Battle of the Atlantic has been called the longest, largest, and most complex naval battle in history. Starting immediately after the European war began, during the Phoney War, the Battle lasted over five years before the German surrender in May 1945. It involved thousands of ships in a theatre covering millions of square miles of ocean. The situation changed constantly, with one side or the other gaining advantage, as participating countries surrendered, joined and even changed sides in the war, and as new weapons, tactics, countermeasures and equipment were developed. The Allies gradually gained the upper hand, overcoming German surface-raiders by the end of 1942 and defeating the U-boats by mid-1943, though losses due to U-boats continued until the war's end. British Prime Minister Winston Churchill later wrote, The only thing that really frightened me during the war was the U-boat peril. I was even more anxious about this battle than I had been about the glorious air fight called the Battle of Britain. On the 5th of March 1941, the First Lord of the Admiralty, A. V. Alexander, asked Parliament for many more ships and great numbers of men to fight the Battle of the Atlantic, which he compared to the Battle of France fought the previous summer. The first meeting of the Cabinet's Battle of the Atlantic Committee was on the 19th of March. Churchill claimed to have coined the phrase Battle of the Atlantic shortly before Alexander's speech, but there are several examples of earlier usage.
What was the duration of the Battle of the Atlantic?
The Battle of the Atlantic lasted from 1939 to the defeat of Nazi Germany in 1945. It was the longest continuous military campaign in World War II, stretching over five years before the German surrender in May 1945.
Who participated in the Battle of the Atlantic?
The campaign pitted U-boats and other warships of the German navy and aircraft of the air force against the Royal Navy, Royal Canadian Navy, United States Navy, and Allied merchant shipping. The Germans were joined by submarines of the Italian royal navy after Germany's Axis ally Italy entered the war on the 10th of June 1940.
When did the United States enter the Battle of the Atlantic?
Ships and aircraft of the United States began aiding the campaign on the 13th of September 1941. The United States officially entered the war in December 1941, leading to the organization of a Mid-Ocean Escort Force of British, Canadian, and American destroyers and corvettes.
What was the outcome of the Battle of the Atlantic?
The outcome of the battle was a strategic victory for the Allies, as the German tonnage war failed. The Allies lost 3,500 merchant ships and 175 warships in the Atlantic for the loss of 783 U-boats and 47 German surface warships.
How did the Battle of the Atlantic affect the United Kingdom?
The United Kingdom required more than a million tons of imported material per week to survive and fight, making the nation highly dependent on imported goods. Without these supplies, the British war effort would collapse, and the nation would be forced to surrender.
The early U-boat operations from the French bases were spectacularly successful. This was the heyday of the great U-boat aces like Günther Prien of U-47, Otto Kretschmer, Joachim Schepke, Engelbert Endrass, Victor Oehrn and Heinrich Bleichrodt. U-boat crews became heroes in Germany. From June until October 1940, over 270 Allied ships were sunk; this period was referred to by U-boat crews as the Happy Time. Churchill would later write: the only thing that ever frightened me during the war was the U-boat peril. The biggest challenge for U-boats was to find the convoys in the vastness of the ocean. The Germans had a handful of very long-range Focke-Wulf Fw 200 Condor aircraft based at Bordeaux and Stavanger, which were used for reconnaissance. The Condor was a converted civilian airliner, a stop-gap solution for. Due to ongoing friction between the and, the primary source of convoy sightings was the U-boats themselves. Since a submarine's bridge was very close to the water, their range of visual detection was short. The best source proved to be the codebreakers of who had succeeded in deciphering the British Naval Cypher No. 3, allowing the Germans to estimate where and when convoys could be expected. In response, the British applied the techniques of operations research and developed some counterintuitive solutions for protecting convoys. Realising the area of a convoy increased by the square of its perimeter, they determined that the same number of ships and escorts would be better protected in a single convoy than two. A large convoy was as difficult to locate as a small one. Reduced frequency also reduced the chances of detection, as fewer large convoys could carry the same amount of cargo, while large convoys take longer to assemble. Therefore, a few large convoys with apparently few escorts were safer than many small convoys with a higher ratio of escorts to merchantmen. Instead of attacking the Allied convoys singly, U-boats were directed to work in wolf packs coordinated by radio. The boats spread out into a long patrol line that bisected the path of the Allied convoy routes. Once in position, the crew studied the horizon through binoculars looking for masts or smoke, or used hydrophones to pick up propeller noises. When one boat sighted a convoy, it would report the sighting to U-boat headquarters, shadowing and continuing to report as needed until other boats arrived, typically at night. Instead of being faced by single submarines, the convoy escorts then had to cope with groups of up to half a dozen U-boats attacking simultaneously. The most daring commanders, such as Kretschmer, penetrated the escort screen and attacked from within the columns of merchantmen. The escort vessels, which were too few in number and often lacking in endurance, had no answer to multiple submarines attacking on the surface at night, as their ASDIC worked well only against underwater targets. Early British marine radar, working in the metric bands, lacked target discrimination and range. Corvettes were too slow to catch a surfaced U-boat. Pack tactics were first used successfully in September and October 1940 to devastating effect, in a series of convoy battles. On the 21st of September, convoy HX 72 of 42 merchantmen was attacked by a pack of four U-boats, which sank eleven ships and damaged two over the course of two nights. In October, the slow convoy SC 7, with an escort of two sloops and two corvettes, was overwhelmed, losing 59% of its ships. The battle for HX 79 in the following days was in many ways worse for the escorts than for SC 7. The loss of a quarter of the convoy without any loss to the U-boats, despite a very strong escort (two destroyers, four corvettes, three trawlers, and a minesweeper) demonstrated the effectiveness of the German tactics against the inadequate British anti-submarine methods. On the 1st of December, seven German and three Italian submarines caught HX 90, sinking 10 ships and damaging three others. At the end of 1940, the Admiralty viewed the number of ships sunk with growing alarm. Damaged ships might survive but could be out of commission for long periods. Two million gross tons of merchant shipping, 13% of the fleet available to the British, were under repair and unavailable, which had the same effect in slowing down cross-Atlantic supplies. Nor were the U-boats the only threat. Following some early experience in support of the war at sea during Operation Weserübung, the began to take a toll of merchant ships. Martin Harlinghausen and his recently established command, contributed small numbers of aircraft to the Battle of the Atlantic from 1941 onwards. These were primarily Fw 200 Condors. The Condors also bombed convoys that were beyond land-based fighter cover and thus defenceless. Initially, the Condors were very successful, claiming 365,000 tons of shipping in early 1941. These aircraft were few in number, and directly under control; the pilots had little specialised training for anti-shipping warfare, limiting their effectiveness. Italian submarines in the Atlantic The Germans received help from their allies. From August 1940, a flotilla of 27 Italian submarines operated from the BETASOM base in Bordeaux to attack Allied shipping in the Atlantic, initially under the command of Rear Admiral Angelo Parona, then of Rear Admiral Romolo Polacchini and finally of ship-of-the-line captain Enzo Grossi. The Italian submarines had been designed to operate in a different way than U-boats, and they had flaws that needed to be corrected (for example huge conning towers, slow speed when surfaced, lack of modern torpedo fire control), which meant that they were ill-suited for convoy attacks, and performed better when hunting down isolated merchantmen on distant seas, taking advantage of their superior range and living standards. Initial operation met with little success (only 65343 GRT sunk between August and December 1940), but the situation improved gradually, and up to August 1943 the 32 Italian submarines that operated there sank 109 ships of 593,864 tons, for 17 subs 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 also successful with their use of human torpedo chariots, disabling several British ships in Gibraltar. Despite these successes, the Italian intervention was not favourably regarded by Dönitz, who characterised Italians as inadequately disciplined and unable to remain calm in the face of the enemy. They were unable to co-operate in wolf pack tactics or even reliably report contacts or weather conditions, and their area of operation was moved away from that of the Germans. Amongst the more successful Italian submarine commanders who operated in the Atlantic were Carlo Fecia di Cossato, commander of the, and Gianfranco Gazzana-Priaroggia, commander of and then of.
Surface Raiders And The Black Pit
Despite their success, U-boats were still not recognised as the foremost threat to the North Atlantic convoys. With the exception of men like Dönitz, most naval officers on both sides regarded surface warships as the ultimate commerce destroyers. For the first half of 1940, there were no German surface raiders in the Atlantic because the German Fleet had been concentrated for the invasion of Norway. The sole pocket battleship raider, Admiral Graf Spee, had been stopped at the Battle of the River Plate by an inferior and outgunned British squadron. From mid-1940 a small but steady stream of warships and armed merchant raiders set sail from Germany for the Atlantic. The power of a raider against a convoy was demonstrated by the fate of convoy HX 84, attacked by the pocket battleship on the 5th of November 1940. Admiral Scheer quickly sank five ships and damaged several others as the convoy scattered. Only the sacrifice of the escorting armed merchant cruiser (whose commander, Edward Fegen, was awarded a posthumous Victoria Cross) and failing light allowed the other merchantmen to escape. The British suspended North Atlantic convoys and the Home Fleet put to sea in an unsuccessful attempt to intercept Admiral Scheer, which disappeared into the South Atlantic. She reappeared in the Indian Ocean the following month. Other German surface raiders now began to make their presence felt. On Christmas Day 1940, the cruiser attacked the troop convoy WS 5A, but was driven off by the escorting cruisers. Admiral Hipper had more success two months later, on the 12th of February 1941, when she found the unescorted convoy SLS 64 of 19 ships, sinking seven. In January 1941, the battleships and put to sea from Germany to raid the shipping lanes in Operation Berlin. With so many German raiders at large in the Atlantic, the British were forced to provide battleship escorts to as many convoys as possible. This twice saved convoys from slaughter by the German battleships. In February, the old battleship deterred an attack on HX 106. A month later, SL 67 was saved by the presence of. In May, the Germans mounted the most ambitious raid of all: Operation Rheinübung. The new battleship and the cruiser put to sea to attack convoys. A British fleet intercepted the raiders off Iceland. In the Battle of the Denmark Strait, the battlecruiser was blown up and sunk, but Bismarck was damaged and had to run to France. HMS Hood 1920, Royal Navy Bismarck nearly reached her destination, but was disabled by an airstrike from the carrier Ark Royal, and then sunk by the Home Fleet the next day. Her sinking marked the end of the warship raids. The advent of long-range search aircraft, notably the unglamorous but versatile PBY Catalina, largely neutralised surface raiders. In February 1942, Scharnhorst, Gneisenau and Prinz Eugen moved from Brest back to Germany in the Channel Dash. While this was an embarrassment for the British, it was the end of the German surface threat in the Atlantic. The loss of Bismarck, the destruction of the network of supply ships that supported surface raiders, the repeated damage to the three ships by air raids, the entry of the United States into the war, Arctic convoys, and the perceived invasion threat to Norway had persuaded Hitler and the naval staff to withdraw. Escort groups (March, May 1941) The disastrous convoy battles of October 1940 forced a change in British tactics. The most important of these was the introduction of permanent escort groups to improve the coordination and effectiveness of ships and men in battle. British efforts were helped by a gradual increase in the number of escort vessels available as the old ex-American destroyers and the new British- and Canadian-built s were now coming into service in numbers. Many of these ships became part of the huge expansion of the Royal Canadian Navy, which grew from a handful of destroyers at the outbreak of war to take an increasing share of convoy escort duty. Others of the new ships were crewed by Free French, Norwegian and Dutch, but these were a tiny minority of the total number, and directly under British command. By 1941 American public opinion had begun to swing against Germany, but the war was still essentially Great Britain and the Empire against Germany. Initially, the new escort groups consisted of two or three destroyers and half a dozen corvettes. Since two or three of the group would usually be in dock repairing weather or battle damage, the groups typically sailed with about six ships. The training of the escorts also improved as the realities of the battle became obvious. A new base was set up at Tobermory in the Hebrides to prepare the new escort ships and their crews for the demands of battle under the strict regime of Vice-Admiral Gilbert O. Stephenson. In February 1941, the Admiralty moved the headquarters of Western Approaches Command from Plymouth to Liverpool, where much closer contact with, and control of, the Atlantic convoys was possible. Greater cooperation with supporting aircraft was also achieved. In April, the Admiralty took over operational control of Coastal Command aircraft. Tactically, new short-wave radar sets that could detect surfaced U-boats and were suitable for both small ships and aircraft began to arrive during 1941. The impact of these changes first began to be felt in the battles in early 1941. In early March, Prien in U-47 failed to return from patrol. Two weeks later, in the battle of Convoy HX 112, the newly formed 3rd Escort Group of four destroyers and two corvettes held off the U-boat pack. U-100 was detected by the primitive radar on the destroyer, rammed and sunk. Shortly afterwards U-99 was also caught and sunk, its crew captured. Dönitz had lost his three leading aces: Kretschmer, Prien, and Schepke. Dönitz now moved his wolf packs further west, in order to catch the convoys before the anti-submarine escort joined. This new strategy was rewarded at the beginning of April when the pack found Convoy SC 26 before its anti-submarine escort had joined. Ten ships were sunk, but another U-boat was lost. The field of battle widens (June, December 1941) Growing American activity right|A SB2U Vindicator scout bomber from USS Ranger flies anti-submarine patrol over Convoy WS-12, en route to Cape Town, the 27th of November 1941. The convoy was one of many escorted by the US Navy on Neutrality Patrol, before the US officially entered the war. In June 1941, the British decided to provide convoy escort for the full length of the North Atlantic crossing. To this end, the Admiralty asked the Royal Canadian Navy on the 23rd of May, to assume the responsibility for protecting convoys in the western zone and to establish the base for its escort force at St. John's, Newfoundland. On the 13th of June 1941, Commodore Leonard Murray, Royal Canadian Navy, assumed his post as Commodore Commanding Newfoundland Escort Force, under the overall authority of the Commander-in-Chief, Western Approaches, at Liverpool. Six Canadian destroyers and 17 corvettes, reinforced by seven destroyers, three sloops, and five corvettes of the Royal Navy, were assembled for duty in the force, which escorted the convoys from Canadian ports to Newfoundland and then on to a meeting point south of Iceland, where the British escort groups took over. By 1941, the United States was taking an increasing part in the war, despite its nominal neutrality. In April 1941 President Roosevelt extended the Pan-American Security Zone east almost as far as Iceland. British forces occupied Iceland when Denmark fell to the Germans in 1940; the US was persuaded to provide forces to relieve British troops on the island. American warships began escorting Allied convoys in the western Atlantic as far as Iceland, and had several hostile encounters with U-boats. In June 1941, the US realised the tropical Atlantic had become dangerous for unescorted American as well as British ships. On the 21st of May, an American vessel carrying no military supplies, was sunk by west of Freetown, Sierra Leone. When news of the sinking reached the US, few shipping companies felt truly safe anywhere. As Time magazine noted in June 1941, if such sinkings continue, U.S. ships bound for other places remote from fighting fronts, will be in danger. Henceforth the U.S. would either have to recall its ships from the ocean or enforce its right to the free use of the seas. A Mid-Ocean Escort Force of British, Canadian, and American destroyers and corvettes was organised following the declaration of war by the United States in December 1941. At the same time, the British were working on technical developments to address the German submarine superiority. Though these were British inventions, the critical technologies were provided freely to the US, which then renamed and manufactured them. Likewise, the US provided the British with Catalina flying boats and Liberator bombers that were important contributions to the war effort. Catapult aircraft merchantmen Sea Hurricane Mk IA on the catapult of a CAM ship Aircraft ranges were constantly improving, but the Atlantic was far too large to be covered completely by land-based types. A stop-gap measure was instituted by fitting ramps to the front of some of the cargo ships known as catapult aircraft merchantmen (CAM ships), equipped with a lone expendable Hurricane fighter aircraft. When a German bomber approached, the fighter was launched off the end of the ramp with a large rocket to shoot down or drive off the German aircraft, the pilot then ditching in the water and, in the best case, recovered by ship. Nine combat launches were made, resulting in the destruction of eight Axis aircraft for the loss of one Allied pilot. Axis aircraft, mostly Fw 200 Condors, performing shadow surveillance, tailing the convoy out of range of the convoy's guns, posed a serious risk of reporting back the convoy's course and position so that U-boats could then be directed on to the convoy. Although CAM ships and their Hurricanes did not down a great number of enemy aircraft, they were intended to deter or dispel this surveillance threat, and, in this specialized function, may have covered their cost in fewer ship losses overall. High-frequency direction-finding One of the more important developments was ship-borne direction-finding radio equipment, known as HF/DF (high-frequency direction-finding, or Huff-Duff), which started to be fitted to escorts from February 1942. These sets were common items of equipment by early 1943. HF/DF let an operator determine the direction of a radio signal, regardless of whether the content could be read. Since the wolf pack relied on U-boats reporting convoy positions by radio, there was a steady stream of messages to intercept. An escort could then run in the direction of the signal and attack the U-boat, or at least force it to submerge (causing it to lose contact), which might prevent an attack on the convoy. When two ships fitted with HF/DF accompanied a convoy, a fix on the transmitter's position, not just direction, could be determined. The standard approach of anti-submarine warships was immediately to run-down the bearing of a detected signal, hoping to spot the U-boat on the surface and make an immediate attack. Range could be estimated by an experienced operator from the signal strength. Usually, the target was found visually. If the submarine was slow to dive, the guns were used; otherwise, an ASDIC search was started where the swirl of water of a crash-diving submarine was observed. In good visibility, a U-boat might try and outrun an escort on the surface whilst out of gun rangemost U-boat types had a faster maximum speed on the surface than, for instance, a Flower-class corvette, while a Black Swan-class sloop was only marginally faster. The British also made extensive use of shore HF/DF stations to keep convoys updated with positions of U-boats. HF/DF was also installed on American ships. The radio technology behind direction finding was simple and well understood by both sides, but the technology commonly used before the war used a manually-rotated aerial to fix the direction of the transmitter. This was delicate work, took quite a time to accomplish to any degree of accuracy, and since it only revealed the line along which the transmission originated a single set could not determine if the transmission was from the true direction or its reciprocal 180 degrees in the opposite direction. Two sets were required to fix the position. Believing this to still be the case, German U-boat radio operators considered themselves fairly safe if they kept messages short. The British developed an oscilloscope-based indicator which instantly fixed the direction and its reciprocal the moment a radio operator touched his Morse key. It worked simply with a crossed pair of conventional and fixed directional aerials, the oscilloscope display showing the relative received strength from each aerial as an elongated ellipse showing the line relative to the ship. The innovation was a sense aerial, which, when switched in, suppressed the ellipse in the wrong direction, leaving only the correct bearing. With this, there was hardly any need to triangulate, the escort could just run down the precise bearing provided, estimating range from the signal strength, and use look-outs or radar for final positioning. Many U-boat attacks were suppressed and submarines sunk in this way. Enigma cipher The way Dönitz conducted the U-boat campaign required relatively large volumes of radio traffic between U-boats and headquarters. This was thought to be safe, as the radio messages were encrypted using the Enigma cipher machine, which the Germans considered unbreakable. In addition, the used much more secure operating procedures than the Army or Air Force. The machine's three rotors were chosen from a set of eight (rather than the other services' five). The rotors were changed every other day using a system of key sheets and the message settings were different for every message and determined from bigram tables that were issued to operators. In 1939, it was generally believed at the British Government Code and Cypher School at Bletchley Park that naval Enigma could not be broken. Only the head of the German Naval Section, Frank Birch, and the mathematician Alan Turing believed otherwise. The British codebreakers needed to know the wiring of the special naval Enigma rotors. The capture of several Enigma rotors during the sinking of by in February 1940 provided this information. In early 1941, the Royal Navy made a concerted effort to assist the codebreakers, and on the 9th of May crew members of the destroyer boarded and recovered cryptologic material, including bigram tables and current Enigma keys. The captured material allowed all U-boat traffic to be read for several weeks, until the keys ran out; the familiarity codebreakers gained with the usual content of messages helped in breaking new keys. In August 1940, the British began use of their bombe computer which, when presented with an intercepted German Enigma message, suggested possible settings with which the Enigma cipher machine had been programmed. A reverse-engineered Enigma machine in British hands could then be programmed with each set of suggested settings in turn until the message was successfully deciphered. Throughout late 1941, Enigma intercepts (combined with HF/DF) enabled the British to plot the positions of U-boat patrol lines and route convoys around them. Merchant ship losses dropped by over two-thirds in July 1941, and losses remained low until November. This Allied advantage was offset by the growing numbers of U-boats coming into service. The Type VIIC began reaching the Atlantic in large numbers in 1941; by the end of 1945, 568 had been commissioned. Although the Allies could protect their convoys in late 1941, they were not sinking many U-boats. The Flower-class corvette escorts could detect and defend, but were not fast enough to attack effectively. U-boat captured by an aircraft A Coastal Command Hudson of No. 269 Squadron RAF captured U-570 on the 27th of August 1941 about south of Iceland. Squadron Leader J. Thompson sighted the U-boat on the surface, immediately dived at his target, and released four depth charges as the submarine crash dived. The U-boat surfaced again, crewmen appeared on deck, and Thompson engaged them with his aircraft's guns. The crewmen returned to the conning tower under fire. A few moments later, a white flag and a similarly coloured board were displayed. Thompson called for assistance and circled the German vessel. A Catalina from 209 Squadron took over watching the damaged U-boat until the arrival of the armed trawler Kingston Agate under Lt Henry Owen L'Estrange. The following day the U-boat was beached in an Icelandic cove. No codes or secret papers were recovered, but the British now possessed a complete U-boat. After a refit, U-570 was commissioned into the Royal Navy as. Mediterranean diversion In October 1941, Hitler ordered Dönitz to move U-boats into the Mediterranean Sea to support German operations in that theatre. The resulting concentration near Gibraltar produced a series of battles around the Gibraltar and Sierra Leone convoys. In December 1941, Convoy HG 76 sailed, escorted by the 36th Escort Group of two sloops and six corvettes under Captain Frederic John Walker, reinforced by the first of the new escort carriers, and three destroyers from Gibraltar. The convoy was immediately intercepted by the waiting U-boat pack, resulting in a brutal five-day battle. Walker was a tactical innovator and his ships' crews were highly trained. The presence of an escort carrier meant U-boats were frequently sighted and forced to dive before they could get close to the convoy, at least until Audacity was sunk after two days. The five-day battle cost the Germans five U-boats (four sunk by Walker's group), while the British lost Audacity, a destroyer, and only two merchant ships. The battle was the first clear Allied convoy victory. Through dogged effort, the Allies slowly gained the upper hand until the end of 1941. Although Allied warships failed to sink U-boats in large numbers, most convoys evaded attack completely. Shipping losses were high, but manageable. Operation Drumbeat (January, June 1942) The attack on Pearl Harbor and the subsequent German declaration of war on the United States had an immediate effect on the campaign. Dönitz planned to attack shipping off the American East Coast. He had only five Type IX boats able to reach US waters for Operation Drumbeat (Paukenschlag), sometimes called the second happy time by the Germans. The US, having no direct experience of modern naval war on its own shores, did not employ a blackout. U-boats stood off shore at night and picked out ships silhouetted against city lights. Admiral Ernest King, Commander-in-Chief United States Fleet (Cominch), who disliked the British, initially rejected Royal Navy calls for a coastal blackout or convoy system. King has been criticised for this decision, but his defenders argue the US destroyer fleet was limited (partly because of the sale of 50 old destroyers to Britain earlier in the war), and King claimed it was far more important that destroyers protect Allied troop transports than merchant shipping. His ships were also busy convoying Lend-Lease material to the Soviet Union, as well as fighting the Japanese in the Pacific. King could not require coastal blackouts, the Army had legal authority over all civil defence, and did not follow advice the Royal Navy (or Royal Canadian Navy) provided that even unescorted convoys would be safer than merchants sailing individually. No troop transports were lost, but merchant ships sailing in US waters were left exposed and suffered accordingly. Britain eventually had to build coastal escorts and provide them to the US in a reverse Lend Lease, since King was unable (or unwilling) to make any provision himself. The first U-boats reached US waters on the 13th of January 1942. By the time they withdrew on the 6th of February, they had sunk 156,939 tonnes of shipping without loss. The first batch of Type IXs was followed by more Type IXs and Type VIIs supported by Type XIV Milk Cow tankers which provided refuelling at sea. They sank 397 ships totalling over 2 million tons. In 1943, the United States launched over 11 million tons of merchant shipping; that number declined in the later war years, as priorities moved elsewhere. In May, King (by this time both Cominch and CNO) finally scraped together enough ships to institute a convoy system. This quickly led to the loss of seven U-boats. The US did not have enough ships to cover all the gaps; the U-boats continued to operate freely during the Battle of the Caribbean and throughout the Gulf of Mexico (where they effectively closed several US ports) until July, when the British-loaned escorts began arriving. These included 24 anti-submarine armed trawlers. The institution of an interlocking convoy system on the American coast and in the Caribbean Sea in mid-1942 resulted in an immediate drop in attacks in those areas. As a result of the increased coastal convoy escort system, the U-boats' attention was shifted back to the Atlantic convoys. For the Allies, the situation was serious but not critical throughout much of 1942. Battle returns to the mid-Atlantic (July 1942 , February 1943) With the US finally arranging convoys in their sector of the Atlantic, ship losses to the U-boats quickly dropped, and Dönitz realised his U-boats were better used elsewhere. On the 19th of July 1942, he ordered the last boats to withdraw from the United States Atlantic coast; by the end of July 1942 he had shifted his attention back to the North Atlantic, where Allied aircraft could not provide cover, i.e. the Black Pit. Convoy SC 94 marked the return of the U-boats to the convoys from Canada to Britain. The command centre for the submarines operating in the West, including the Atlantic also changed, moving to a newly constructed command bunker at the Château de Pignerolle just east of Angers on the Loire river. The headquarters was commanded by Hans-Rudolf Rösing. There were enough U-boats spread across the Atlantic to allow several wolf packs to attack many different convoy routes. Often as many as 10 to 15 boats would attack in one or two waves, following convoys like SC 104 and SC 107 by day and attacking at night. Convoy losses quickly increased and in October 1942, 56 ships of over 258,000 tonnes were sunk in the air gap between Greenland and Iceland. U-boat losses also climbed. In the first six months of 1942, 21 were lost, less than one for every 40 merchant ships sunk. In the last six months of 1942, 66 were sunk, one for every 10 merchant ships, almost as many as in the previous two years together. On the 19th of November 1942, Admiral Noble was replaced as Commander-in-Chief of Western Approaches Command by Admiral Sir Max Horton. Horton used the growing number of escorts becoming available to organise support groups, to reinforce convoys that came under attack. Unlike the regular escort groups, support groups were not directly responsible for the safety of any particular convoy. This gave them much greater tactical flexibility, allowing them to detach ships to hunt submarines spotted by reconnaissance or picked up by HF/DF. Where regular escorts would have to break off and stay with their convoy, the support group ships could keep hunting a U-boat for many hours. One tactic introduced by Captain John Walker was the hold-down, where a group of ships would patrol over a submerged U-boat until its air ran out and it was forced to the surface; this might take two or three days. After Convoy ON 154, winter weather provided a brief respite from the fighting in January before convoys SC 118 and ON 166 in February 1943, but in the spring, convoy battles started up again with the same ferocity. There were so many U-boats on patrol in the North Atlantic, it was difficult for convoys to evade detection, resulting in a succession of vicious battles. Western Approaches Tactical Unit Between February 1942 and July 1945, about 5,000 naval officers played war games at Western Approaches Tactical Unit. Many game graduates believed that the battle they fought on the linoleum floor was essential to their subsequent victory at sea. Many game graduates believed that the battle they fought on the linoleum floor was essential to their subsequent victory at sea. Ahead-throwing weapons At the start of World War II, the depth charge was the only weapon available to a vessel for destroying a submerged submarine. Depth charges were dropped over the stern and thrown to the side of a warship travelling at speed. Early models of ASDIC/sonar searched only ahead, astern and to the sides of the vessel that was using it: there was no downward-looking capability. This caused a delay between the last fix obtained on the submarine and the warship's arrival atop that position, after which depth charges could be deployed and sink to the depth at which they set to explode. During these two delays, a capable submarine commander would manoeuvre rapidly to a different position, avoiding the explosions. The depth charges then left an area of disturbed water, through which it was difficult to regain ASDIC/sonar contact. In response to this problem, one of the solutions developed by the Royal Navy was the ahead-throwing anti-submarine weapon, the first of which was Hedgehog. Hedgehog was a multiple spigot mortar, which fired contact-fused bombs ahead of the firing ship while the target was still within the ASDIC beam. These started to be installed on anti-submarine ships from late 1942. The warship could approach slowly (as it did not have to clear the area of exploding depth charges to avoid damage) and so its position was less obvious to the submarine commander as it was making less noise. Because Hedgehog only exploded if it hit the submarine, if the target was missed, there was no disturbed water complicate tracking, and contact would not have been lost in the first place. Squid Introduced in late 1943, Squid improved upon Hedgehog's design. A three-barrelled mortar, it projected charges ahead or abeam; the charges' firing pistols set automatically just before launch. More advanced installations linked Squid to the latest ASDIC sets so that the weapon was fired automatically. Leigh Light Detection by radar-equipped aircraft could suppress U-boat activity over a wide area, but an aircraft attack could only be successful with good visibility. U-boats were relatively safe from aircraft at night for two reasons: 1) radar then in use could not detect them at less than; 2) flares deployed to illuminate any attack gave adequate warning for evasive manoeuvres. The introduction of the Leigh Light by the British in January 1942 solved the second problem, thereby becoming a significant factor in the Battle for the Atlantic. Developed by RAF officer H. Leigh, it was a powerful and controllable searchlight mounted primarily to Wellington bombers and B-24 Liberators. These aircraft first located enemy submarines using air-to-surface-vessel (ASV) radar. Then, about from the target, the Leigh Light would be switched on. It immediately and accurately illuminated the enemy, giving U-boat commanders less than 25 seconds to react before they were attacked with depth charges. The first confirmed kill using this technology was U-502 on the 5th of July 1942. The Leigh Light enabled the British to attack enemy subs on the surface at night, forcing German and Italian commanders to remain underwater especially when coming into port at sub bases in the Bay of Biscay. U-boat commanders who survived such attacks reported a particular fear of this weapon since aircraft could not be seen at night, and the noise of an approaching aircraft was inaudible above the sound of the sub's engines. The common practice of surfacing at night to recharge batteries and refresh air was mostly abandoned as it was safer to perform these tasks during daylight hours when enemy planes could be spotted. Metox receiver By August 1942, U-boats were being fitted with radar detectors to enable them to avoid ambushes by radar-equipped aircraft or ships. The first such receiver, named Metox after its French manufacturer, could pick up the metric radar bands used by early radars. This enabled U-boats to avoid detection by Canadian escorts, which were equipped with obsolete radar sets, and allowed them to track convoys where these sets were in use. It also caused problems for the Germans, sometimes detecting stray radar emissions from distant ships or planes. This caused U-boats to submerge when they were not in danger, preventing them from recharging batteries or using their surfaced speed. Metox provided the U-boat commander with an advantage that had not been anticipated by the British. The Metox set beeped at the pulse rate of the hunting aircraft's radar, about once per second. When the radar operator came within of the U-boat, he changed the range of his radar. With the change of range, the radar doubled its pulse frequency and as a result, the Metox beeping frequency also doubled, warning the commander that he had been detected and that the approaching aircraft was nine miles away. Germans break Admiralty codes In 1941, American intelligence informed Rear Admiral John Henry Godfrey that the UK naval codes could be broken. In March 1942, the Germans broke Naval Cipher 3, used for Anglo-American communication. Eighty per cent of the Admiralty messages from March 1942 to June 1943 were read by the Germans. Sinking of Allied merchant ships increased dramatically. Günter Hessler, Admiral Dönitz's son-in-law and first staff officer at U-boat Command, said: We had reached a stage when it took one or two days to decrypt the British radio messages. On occasions only a few hours were required. We could sometimes deduce when and how they would take advantage of the gaps in our U-boat dispositions. Our function was to close those gaps just before the convoys were due. The code breakers of Bletchley Park assigned only two people to evaluate whether the Germans broke the code. After five months, they determined that the codes were broken. In August 1942, the UK Admiralty was informed, but did not change the codes until June 1943. Captain Raymond Dreyer, deputy staff signals officer at Western Approaches, the British HQ for the Battle of the Atlantic in Liverpool, said: Some of their most successful U-boat pack attacks on our convoys were based on information obtained by breaking our ciphers. Enigma in 1942 On the 1st of February 1942, the switched the U-boats to a new Enigma network, TRITON, which used new, four-rotor Enigma machines. This new key could not be read by codebreakers; the Allies no longer knew where the U-boat patrol lines were. This made it far more difficult to evade contact, and wolf packs ravaged many convoys. This persisted for ten months. To obtain information on submarine movements the Allies had to make do with HF/DF fixes and decrypts of messages encoded on earlier Enigma machines. These messages included signals from coastal forces about U-boat arrivals and departures at their bases in France, and reports from the U-boat training command. From these clues, Commander Rodger Winn's Admiralty Submarine Tracking Room estimated submarine movements, but this information was not enough. On the 30th of October, crewmen from salvaged Enigma material from as she foundered off Port Said. This allowed codebreakers to break TRITON. By December 1942, Enigma decrypts were again disclosing U-boat patrol positions, and shipping losses declined dramatically once more. Climax of the campaign (March, May 1943, Black May) On the 10th of March 1943, the Germans added a refinement to the U-boat Enigma key, blinding Allied codebreakers at Bletchley Park for 9 days. That month saw the battles of convoys UGS 6, HX 228, SC 121, SC 122 and HX 229. 120 ships were sunk worldwide, 82 ships of 476,000 tons in the Atlantic, while 12 U-boats were destroyed. The supply situation in Britain was such that there was talk of being unable to continue the war, with supplies of fuel being particularly low. The situation was so bad that the British considered abandoning convoys entirely. The next two months saw a complete reversal of fortunes. In April, losses of U-boats increased and their kills fell significantly. Only 39 ships of 235,000 tons were sunk in the Atlantic, and 15 U-boats were destroyed. By May, wolf packs no longer had the advantage and that month became known as Black May in the U-boat Arm. The turning point was the battle centred on slow convoy ONS 5 (April, May 1943). Made up of 43 merchantmen escorted by 16 warships, it was attacked by a