The Crucial Battle of the Atlantic During World War II

The Crucial Battle of the Atlantic During World War II

Larry Holzwarth - January 17, 2020

The longest continuous campaign of the Second World War, the Battle of the Atlantic was critical to the success of the Allies. Great Britain required 1 million tons of supplies of all types per week, in order to feed its population and continue the fight against Germany and Italy. The supplies could only arrive, from the Empire and the United States, by ship. In its early days’ success and failure was measured in tonnage; how many tons arrived in Great Britain’s ports, and how many tons was sent to the bottom of the sea by the German Navy and aircraft. During the long campaign, thousands of merchant ships – nearly all manned by civilians – were sunk.

The Crucial Battle of the Atlantic During World War II
Crewman of a US Coast Guard cutter watching a depth charge exploded during an attack on a German U-boat. US Coast Guard

The German surface fleet was not large enough to challenge the Royal Navy at sea, and it used its capital ships as surface raiders to destroy commerce. U-boats lurked in the sea lanes along the Canadian east coast, and after America entered the war along its coast as well. The waters off South America and Africa were also hunting grounds for the Germans. Early in the war surface raiders swept around the Cape of Good Hope into the Indian Ocean. After the surrender of the French, the British Navy also had to contend with the Italian fleet in the Mediterranean. All the while, merchant seamen, in crawling, heavily laden ships, struggled to keep Britain alive. Here is the story of the Battle of the Atlantic during World War II.

The Crucial Battle of the Atlantic During World War II
The German Navy deployed surface raiders to positions at sea in the weeks before the war. Wikimedia

1. Germany deployed many ships just prior to the Invasion of Poland

The Kriegsmarine (German Navy) deployed surface ships and as many U-boats as were ready for sea prior to the attack on Poland. Among their surface ships was a type known to posterity as pocket battleships. Deutschland (later renamed Lutzow) and Admiral Graf Spee were two such ships. Deutschland sank a few merchant ships in the North Atlantic, stopping them and taking prisoner their crews in accordance with prize rules. Admiral Graf Spee evaded detection and embarked on a cruise in the South Atlantic which carried the vessel into the Indian Ocean. The German ship also followed the prize rules as it sank 9 ships totaling just over 50,000 tons.

In December Graf Spee encountered three British cruisers, Ajax, Achilles, and Exeter. In the running gun battle which ensued, Exeter was heavily damaged. Ajax was also badly hit, and Achilles too was hit by the German guns. Graf Spee was also hit, its fuel processing system badly damaged, which left the Germans only about 16 hours of steaming time. It was not enough for the ship to return home, and while under fire repairs were impossible. Its Captain, Hans Langsdorff, steered the ship up the River Plate estuary to the neutral port of Montevideo. Their neutrality laws prohibited a stay of more than 24 hours unless the ship was deemed unseaworthy. There were other neutrality laws which affected the ship as well.

The Crucial Battle of the Atlantic During World War II
Captain Langsdorff used the traditional naval salute to honor the dead of his crew while others favored the Nazi version. Wikimedia

2. The first British naval victory was accomplished by diplomats in Montevideo

Another of the neutrality laws stated that a warship could not leave a neutral port following the departure of a merchant ship “flying the flag of its adversary” for 24 hours. British diplomats demanded the German ship be ordered to leave the port. At the same time, they secretly manipulated the scheduled departures of ships to control the time of Graf Spee’s departure. Their goal was to assemble a more powerful British force to destroy the damaged German ship. Langsdorff asked for two weeks to make repairs on his ship, arguing it was not seaworthy. It was denied.

The Germans released 61 merchant seamen they had taken prisoner, and through the German embassy Langsdorff received instructions from Berlin. He was told that internment in Montevideo was unacceptable. Langsdorff decided that another battle with the British ships would accomplish nothing but casualties, and surrender was unthinkable. He scuttled the ship in the estuary on December 17, 1939 and his crew were sent to Buenos Aires for internment. He committed suicide on December 20 and was buried with the dead from Battle of the River Plate in the Argentinian city.

The Crucial Battle of the Atlantic During World War II
U-boat facilities were quickly established in France to attack the shipping which kept Britain in the war. Wikimedia

3. The German U-boats inflicted severe casualties on the Royal Navy in the early weeks of the war

In September 1939, the Royal Navy deployed submarine-hunting groups centered around an aircraft carrier. Carriers escorted by destroyers and corvettes searched for German submarines, despite the fact that their aircraft lacked suitable weapons to attack them. Their role was to guide the surface ships to the submarine’s position. By the time the attacking vessels arrived, the U-boat was most often submerged and gone. The offensive tactic removed ships from escort duty with the merchant convoys. It also exposed the aircraft carriers to attack. On September 14, three torpedoes were fired by a U-boat at the aircraft carrier Ark Royal. They exploded prematurely, allowing Great Britain’s most modern carrier to escape.

Three days later, another British aircraft carrier, Courageous, was not so lucky. After following the ship for nearly two hours, U-29 fired three torpedoes, two of which struck the British ship on the port side. Flooding shorted out switchboards, and all electrical power was lost. The aircraft carrier rolled over on its side and sank in less than half an hour, with the loss of over five hundred men of its crew. U-29 was depth charged by escorts for nearly four hours before it eluded them and escaped. The Admiralty withdrew its remaining aircraft carriers from hunting submarines until they were better equipped with aircraft capable of attacking their enemy.

The Crucial Battle of the Atlantic During World War II
HMS Royal Oak was sunk while in the Royal Navy’s primary fleet anchorage. Royal Navy

4. The loss of HMS Royal Oak at anchor was an indication of the professionalism of the German Navy

HMS Royal Oak was a battleship of World War I vintage, a veteran of the Battle of Jutland. In October, 1939 the ship was outdated in terms of speed. Nonetheless, the powerful guns carried by the battleship made it a useful weapon for shore bombardment. The ship was at anchor in Scapa Flow, the main fleet anchorage for the Royal Navy. Most of the fleet had been moved out of fear of a German aerial attack. Royal Oak remained its anti-aircraft guns of significant value to defense of the anchorage’s extensive shore facilities. Scapa Flow was considered safe from submarine attack by the British.

They were wrong. On the night of October 13-14, U-47, commanded by Gunther Prien, entered the anchorage on the surface. He took advantage of the moonless night to maneuver his vessel into position and fire four torpedoes. One failed to exit its tube, two missed, and one struck the battleship. Though the crew was alerted by the explosion, none suspected their ship was under submarine attack in the heart of the Royal Navy’s prime anchorage. Prien reloaded his torpedo tubes, fired another salvo, and scored three hits. Royal Oak went down in less than fifteen minutes, over 800 of its crew were killed. The U-boat escaped Scapa Flow, carrying Prien to a hero’s reception in Germany.

The Crucial Battle of the Atlantic During World War II
The Italian Navy provided a serious threat to the British in the spring of 1940. Wikimedia

5. The spring of 1940 created a crisis for the Royal Navy

Several events occurred in 1940 which stretched the Royal Navy to near its breaking point. Germany invaded and occupied Norway, gaining access to its fjords. The French were overrun and surrendered to the Germans. The surrender took the French fleet, then the fourth largest in the world, out of the war. Italy declared war on France and Great Britain. The Italian fleet was an immediate threat in the Mediterranean. So were the ships of the French Navy, if the Germans seized them. The Germans in France threatened Britain with invasion. Ships needed to protect Atlantic convoys were also needed in the Channel, to deter or repel a German attack.

The British lost 23 destroyers between May and July of 1940, losses which crippled their ability to resist the increased U-boat threat. At the same time, more German submarines were made available for service in the Atlantic. The British asked for American help. Fifty World War I era destroyers were “loaned” to the British in exchange for leases of British military bases in Canada, the West Indies, and Bermuda. In reality, the Americans did not want the destroyers back. None of them were equipped with the British version of sonar known as asdic, and some were barely seaworthy. For the British, the rest of 1940 was a time a crisis. For the German Navy, it was known as the Happy Time.

The Crucial Battle of the Atlantic During World War II
German U-boat U-30 sank 17 Allied ships during its career in World War II. Library of Congress

6. The First Happy Time saw the U-boats wreak havoc in the Atlantic

From their new bases in France, German U-boats attacked the Atlantic convoys carrying Great Britain’s lifeblood. During a period of five months, June through October 1940, the U-boats sank more than 270 ships. Merchant captains of newer, faster ships at that period of the war continued to attempt crossings without escort. By necessity, a convoy’s top speed was limited to that of the slowest vessel. Also, some captains did not trust operating in such close quarters in the North Atlantic. Those that did often experienced difficulty keeping station in relation to the rest of the formation. Until September, most U-boats operated singly, rather than in concert with others.

Wolfpack tactics, in which several U-boats attacked a convoy, emerged in the late summer of 1940. On September 21 a convoy of 43 ships, escorted only by an armed merchant cruiser (AMC) was attacked by a wolfpack. The convoy was sighted by Gunther Prien in U-47. Prien was out of torpedoes due to earlier attacks, so he radioed the position and course of the convoy and shadowed it while a pack of six U-boats formed to attack. An escort formed for the convoy as it reached the Western Approaches, but the U-boats attacked and sank 11 ships of over 70,000 total tons.

The Crucial Battle of the Atlantic During World War II
German crewmen aboard a resupply ship, used to keep warships at sea for longer periods. Library of Congress

7. The wolfpacks overwhelmed escorts of slow convoys in October, 1940

On October 5, convoy SC7 formed off Nova Scotia bound for Liverpool and ports in Scotland. The 35 ships included vessels from Greece, Norway, the Netherlands, Sweden, and Great Britain. A single British sloop served as the escort for the crossing, until it met another escort off the Western Approaches. Bad weather forced many ships to scatter six days out, and several were then sighted and sunk by U-boats. On October 17, three more escorts joined the remains of the convoy, which was nonetheless attacked by German submarines, with several more ships lost. The following day two additional escorts arrived but the Germans pressed their attacks.

On the night of October 18, a five U-boat wolfpack attacked the convoy, sinking several more ships, and attacks continued the following day. The escorts were simply overwhelmed. The Germans finally broke off the attacks, after sinking 20 of the 35 ships which had departed Canada. They carried badly needed food, lumber, steel, fuel oil, iron ore, and finished products such as trucks. Nearly 80,000 gross tons of shipping was lost through the U-boat attacks. It was, from the German point of view, the most successful coordinated U-boat attack of the war. For the British it was an unmitigated disaster, a loss of shipping and materiel ill-afforded.

The Crucial Battle of the Atlantic During World War II
German Admiral Karl Doenitz (left) and his Italian counterpart, Angelo Parona. Wikimedia

8. Italian submarines joined the Germans in France in August 1940

Admiral Karl Doenitz commanded the German submarine fleet from the start of the war, taking a personal role in planning specific missions. It was he who planned the wolfpack tactics. In mid-summer, a squadron of Italian submarines arrived at a base established for their use in Bordeaux. The Italians maintained a separate command chain under Admiral Angelo Parona. Parona took his orders from Doenitz. Italian submarines were delegated to patrol the approaches to the Mediterranean and the Atlantic south of Spain. Doenitz was not pleased with the Italian operation and treated them with considerable disdain.

The German Admiral considered his Italian ally unreliable, unsteady in the face of the enemy, and lacking in discipline. He also considered their submarines to be ill-suited for the wolfpack tactics he favored. The Italians operated longer patrols into the areas assigned to them, taking advantage of the superior range and endurance of their submarines. They proved an effective ally in the Battle of the Atlantic, despite Doenitz’s low opinion of them. Before the Italian surrender, 109 ships were lost to their submarines in the Atlantic, accounting for over 500,000 tons lost by the Allies during the campaign.

The Crucial Battle of the Atlantic During World War II
A German heavy cruiser takes aboard one of its Arado seaplanes, used for locating targets at sea. Library of Congress

9. The German raider Admiral Scheer appeared in the Atlantic in late 1940

In late October 1940, the German heavy cruiser Admiral Scheer steamed into the Atlantic through the Denmark Straits and attacked a convoy, sinking five ships and scattering the rest. It was the first action of the most successful raiding cruise of the war. Admiral Scheer both sank merchant ships and took them as prizes, as it operated under the prize rules which required a warning before opening fire. In early 1941, the German cruiser entered the Indian Ocean. The ship did further damage there, successfully eluded more than a half dozen British ships sent to hunt it down, and returned to the Atlantic. In late March the German ship returned to Kiel via the Denmark Strait and Norway.

During its six-month cruise in the Atlantic and Indian Oceans, Admiral Scheer destroyed over 113,000 gross registered tons of shipping, sinking 17 ships. The ship also captured as prizes several merchant ships and tankers. The Royal Navy began a campaign to destroy the German network of supply ships which had supported the cruiser, allowing it to remain at sea for such a long period. The campaign intensified after Bismarck’s failed attempt to conduct surface raiding later in the spring of 1941. By the time Admiral Scheer was ready for sea again, there were no longer the means for the ship to operate independently in the Atlantic, and the planned operation was canceled.

The Crucial Battle of the Atlantic During World War II
The German heavy cruiser Admiral Hipper in waters off Norway. Wikimedia

10. The surface raiders of early 1941 strained the British capacity to protect convoys

While Admiral Scheer was in the Atlantic in December 1940, it allowed a captured ship to broadcast its position deliberately. British ships turned to pursue the cruiser, allowing another heavy cruiser, Admiral Hipper, to break into the Atlantic via the Denmark Strait. Admiral Hipper sank seven ships out of a convoy of 19 it encountered in February, scattering the rest. In January the German battleships Gneisenau and Scharnhorst entered the Atlantic. The Royal Navy was obliged to provide battleships as escorts for convoys when possible. The German battleships could easily outrun British battleships, and outgun British cruisers.

The German battleships remained at sea for 60 days, steaming over 17,000 miles. They ranged from the North Atlantic to the Azores, and returned up the western Atlantic. During the short cruise, they twice encountered British battleships, HMS Malaya and HMS Rodney, though both times they followed orders and did not engage. The two ships sank or captured over 113,000 tons of shipping, accounting for 22 ships. The German Admiral in charge of the operation, Gunther Lutjens, transferred his flag to the battleship Bismarck upon return to Germany. He led the ship on another surface raiding mission in May, in company with the heavy cruiser Prinz Eugen.

The Crucial Battle of the Atlantic During World War II
HMS Hood at anchor circa 1940. Only three of its fourteen hundred-man crew survived its explosion and sinking. Wikimedia

11. Operation Rheinubung was the last of the surface raider sorties in 1941

In May 1941, the German battleship Bismarck sortied in company with the heavy cruiser Prinz Eugen. Under command of Admiral Lutjens – an inveterate Nazi – Bismarck was to enter the Atlantic shipping lanes and interdict convoys bound for the western British ports. The Royal Navy scrambled to meet the German threat. In the Denmark Strait the British battlecruiser Hood and the newest British battleship, Prince of Wales, encountered the German ships. On May 24, 1941, Bismarck sank Hood, pride of the British Navy, after only eight minutes of exchanging fire. 1,414 British sailors went down with their ship.

Prince of Wales was damaged and forced to break off the action. Bismarck too was damaged, leaking oil and down at the bow from a hit by the British battleship. The Royal Navy mustered every available ship to catch Bismarck before it could reach the safety of Brest for repairs. Though damaged, Bismarck had sufficient speed to outrun the British battleships chasing it, and was too powerful for the cruisers which shadowed it to engage alone. While the world listened to news of the chase, and the loss of Hood, Prinz Eugen broke away to attempt commerce raiding on its own. Bismarck shook off its pursuers, and vanished into the North Atlantic murk.

The Crucial Battle of the Atlantic During World War II
The short, violent life of Bismarck destroyed Hitler’s confidence in the German surface fleet. Wikimedia

12. The sinking of Bismarck marked the end of surface raiding by the Kriegsmarine

On May 26, a Catalina flying boat located Bismarck, still bound for Brest, but some 700 nautical miles distant. Aircraft from HMS Ark Royal attacked, and in two separate strikes hit the German battleship with at least two torpedoes. One jammed one of the great ship’s rudders, and the vessel began to steam in a circle. Throughout the night the ship was harassed by British destroyers. On the morning of May 27, the British battleships Rodney and King George V opened fire on the crippled German. Bismarck fought back until its gun turrets were out of action, its decks aflame, and much of its crew dead. Although the British claimed to have sunk the ship with cruiser-launched torpedoes, evidence revealed when the wreck was examined indicated the Germans scuttled the ship.

The loss of Bismarck led Hitler to instruct Admiral Raeder, Commander in Chief of the German Navy, to end surface raiding of convoys in the Atlantic. The remaining capital ships of the Kriegsmarine moved to northern ports by transiting up the Channel, which they did in the face of the British Navy. From there they threatened the convoys moving supplies to the Soviets for the rest of the war. Attacks on Atlantic Convoys were left to the U-boats and when in range of German aviators. Fuel for the surface ships was also restricted. The German surface fleet became a fleet in being, a threat due to its existence which the British were forced to counter.

The Crucial Battle of the Atlantic During World War II
British sailors use steam hoses to clear ice from deck equipment while operating in the North Atlantic. Wikimedia

13. The British Royal Navy battled the elements as well as the Germans

The North Atlantic weather was as much of an enemy to the British Navy as the Kriegsmarine. Ships assigned to escort convoys faced often terrible weather. Ships were coated with ice in winter, battered by storms year-round, and required extensive maintenance and repair. The number of ships in yards to repair storm and battle damage limited those available for escort duty. The conditions were also exhausting for the crews of the escort ships. The British absorbed the lessons learned from the heavy losses incurred from weather and the Germans and created a new training facility for ships and crews in the Hebrides. The Admiralty also took over control of the RAF’s Coastal Command, to attack U-boats in the Western Approaches.

Admiralty’s command over the battle was shifted to Liverpool. By the late spring of 1941, the British adopted a new means of escorting convoys. They established better control of the merchantmen of which they were comprised, and better asdic and radar with which to locate U-boats. In June 1941, the Admiralty decided to escort convoys all the way across the Atlantic with full escorts of destroyers and corvettes. The expanding destroyer fleet of His Majesty’s Canadian Navy made the decision possible. The United States expanded its security zone nearly to Iceland, garrisoned the island, and began to escort ships as far as the new American base.

The Crucial Battle of the Atlantic During World War II
An American destroyer conducting a depth charge attack in 1942. US Coast Guard

14. Hostilities between the Americans and Germans increased throughout 1941

In June 1941, an American-flagged merchant ship, Robin Moor, was stopped in international waters by U-69, in the South Atlantic. Its manifest was examined by the Germans, who then ordered its crew into its four lifeboats. The Germans sank the abandoned vessel with the U-boat’s deck gun and a single torpedo. None of the ship’s cargo were considered war materials. The only munitions aboard were shotgun shells and .22 caliber rifles, bound for a sporting goods merchant. The Germans had no legal grounds to support sinking a ship of a neutral country in international waters. The argument over the legality of the action was dwarfed by outrage over the treatment of the crew.

The Germans did not broadcast a message of the crew’s position, and they drifted at sea for nearly three weeks. The four boats drifted apart and were eventually rescued by two different ships. When the sinking became known in Washington, German assets in the United States were frozen, and all consulates were ordered closed. In Germany, the Nazis reciprocated in kind. Admiral Ernest King, Commander in Chief of the Atlantic fleet, authorized American warships to act in their own defense, or the defense of American shipping, when threatened by German or Italian submarines.

The Crucial Battle of the Atlantic During World War II
The Germans used converted and modified airliners as long-range bombers against targets on land and sea. Wikimedia

15. Merchant ships were attacked with long-range aircraft as well as from the sea

The Germans used long-range bombers to attack convoys and escorts, which included bombing raids on ships in the Channel Ports. Ranges extended as the war went on, and fighters from land bases often could not intervene. The British arrived at a scheme in which catapults were installed in merchant ships, equipped with a single Hawker Hurricane fighter. The ships were called Catapult Armed Merchantmen (CAM). CAMs were designed to launch the fighter to attack the oncoming bombers, after which the pilot would either ditch in the sea or parachute into it, where he would be picked up by a British vessel or patrol boat.

Nine times CAMs were used in combat during the Battle of the Atlantic. The pilots succeeded in shooting down 8 German aircraft, and only one British pilot was lost. It was impossible to estimate the number of ships saved by the operation. The CAM ships were crewed by the Royal Navy, though they carried a full load of cargo. The pilots were recruited from the Royal Air Force. Due to weather conditions, the CAMs frequently could not launch their aircraft and by 1943 the program was disbanded. Before it was, 35 CAM ships were deployed. Twelve of them were sunk by the Germans and Italians.

The Crucial Battle of the Atlantic During World War II
The bridge of an escort ship with ships of a convoy in the distance. Wikimedia

16. The British achieved their first clear victory in a convoy battle in late 1941

In October 1941, under the direct orders of Adolf Hitler, Doenitz deployed U-boats to the Mediterranean, in support of German operations in North Africa. In December, convoy HG 76 (HG stood for Homeward from Gibraltar) departed for Liverpool. Among its escorts was HMS Audacity, a smaller aircraft carrier known as an escort carrier. The 32-ship convoy had an escort of as many as 17 warships at different times, and another British submarine hunter group was in the nearby vicinity. Despite the strong escort, Doenitz’s U-boats attacked using wolfpack tactics.

Aircraft from Audacity and Gibraltar forced the U-boats to submerge or drove them off. They were pursued by destroyers, corvettes and sloops. By the time the Germans broke off the string of submarine attacks on December 23, Audacity and a destroyer were sunk. So were two merchant ships. The rest of the convoy got through safely to Liverpool. The Germans claimed about 4,000 tons of shipping from the convoy, though they lost five U-boats and their crews. The new British tactics forced Doenitz to recall his remaining boats, and what the Germans called the Happy Time came to an end.

The Crucial Battle of the Atlantic During World War II
Two formerly American destroyers which were transferred to the British in the Destroyers for Bases Agreement. Wikimedia

17. The Second Happy Time began with American entry into the war

Before the declaration of war between the United States and Germany, American destroyers had fired on several U-boats. One, USS Reuben James, had been sunk by the Germans. The United States Coast Guard had also destroyed a German weather station in Greenland. When a declaration of war formalized what was already a fact of life in the Atlantic, Doenitz deployed his long-range U-boats on the American East Coast. U-boats were off American shores by the second week of 1942. There they discovered that the US did not employ a coastal blackout at night. They also found few destroyers prowling the American coastal waters.

Ships moving along the coast were silhouetted against the lights of the shoreline, creating perfect targets for the German skippers, many of them experienced by more than two years of war. The first wave of U-boats remained on the American coastline for three weeks before returning to France. By February 6, when the last boat departed for home, 156,000 tons of American shipping had gone to the bottom. Many of the sinkings were seen from the shore. The U-boats left having been unhindered by the American Navy. It was the beginning of what the Germans called the Second Happy Time, and a worse disaster for the United States than Pearl Harbor had been.

The Crucial Battle of the Atlantic During World War II
A U-boat under aerial attack in the South Atlantic. US Navy

18. The US Navy did not have the ships to convoy along the American coast

Admiral Ernest King, in command of the United States Navy, lacked the ships necessary to convoy merchantmen along American shores. He needed those he did have to escort lend-lease convoys to Britain and Murmansk, and especially troopships. From January until August 1942 the German U-boats often had a free hand off American shores, in the Caribbean, and in the Gulf of Mexico. Several Gulf ports were effectively blockaded by U-boats. The situation worsened as the spring dragged into summer. By August, 609 ships were sunk by the Germans, a total of 3.1 million tons of shipping.

Most of the casualties were the result of the carnage at sea during America’s first eight months of the European war were civilians. They were the crews of the merchant ships and tankers that went with their ships to the bottom. American air reconnaissance was ineffective. So were air defenses. The British looked at the sinkings with alarm, and made several recommendations on how they could be reduced, based on their own bitter experience. They were mostly ignored. Not all of the ships destroyed in American waters were US-flagged vessels, but the majority were.

The Crucial Battle of the Atlantic During World War II
The U-boat onslaught forced changes to American sailing regulations implemented by the Coast Guard. National Archives

19. The US Coast Guard would not allow ships to sail singly

Coast Guard Rear Admiral Adolphus Andrews commanded the area from Maine to North Carolina. In April, in response to the massive losses and his own shortage of vessels to protect shipping, he restricted movement to daylight hours. He also restricted ships from moving alone, and established convoys which worked up and down the coast. They moved from one protected anchorage to another, paused for the night, and proceeded the following day. The preceding month, March 1942, the Royal Navy transferred several escort vessels to the waters off the United States. They also established a Naval Air Station in Rhode Island, which was transferred later in the year to Trinidad.

American naval officers viewed British protection as humiliating and blamed Roosevelt for having given away the large contingent of destroyers earlier in the war. His supporters argued that the destroyers were obsolete as anti-submarine weapons. By August, increased patrols by the British and American Navies and the US Coast Guard reduced the number of lost ships and inflicted casualties on the U-boats. US and British shipbuilding began to produce more ships than were lost by the end of 1942, and improved sonar and anti-submarine warfare capabilities reduced German effectiveness.

The Crucial Battle of the Atlantic During World War II
German U-185 foundering in the Atlantic late in the war. US Navy

20. Doenitz returned to concentrating on the mid-Atlantic sea lanes

In late summer, 1942, the German U-boats returned to operations in the open oceans, withdrawing from the American coast. In Germany, naval construction on all surface ships was halted, and all was concentrated on the U-boat fleet. Heavy guns for German capital ships began to loom on beach fortifications, Hitler’s Atlantic Wall. In autumn, U-boat losses began to mount, while the number of Allied ships lost to the wolfpacks continued to be dangerously high. New weapons, including the British-developed Hedgehog, joined the fight.

Depth charges were dropped from the stern of escort ships, or ejected by launchers to the side and behind. Hedgehogs were launched ahead of the ship, thrown forward, into the asdic beam projected by the vessel. In action, they proved far more effective than depth charges. Radar-equipped aircraft, also developed by the British, allowed long-range airplanes to detect and harass submarines while they vectored in surface ships to destroy them. They also were equipped with effective weapons against U-boats. As 1943 began the Allies started to gain the upper hand in the Battle of the Atlantic.

The Crucial Battle of the Atlantic During World War II
Crewmen from HMS Petard recovered TRITON code documents, but their attempt to capture an Enigma machine cost them their lives. Wikimedia

21. Codebreakers contributed to the Allied effectiveness throughout much of the battle

The story of the Polish and British cracking of the German codes processed through Enigma machines is far too extensive for inclusion here. What is pertinent is the German Navy’s use of an Enigma-based code called TRITON beginning in 1942. USS TRITON used the four-wheel version of the Enigma system. The change to TRITON temporarily left the British codebreakers in the dark. In late October, 1942, a German U-boat was attacked by HMS Petard in the Mediterranean. In company with other British destroyers, Petard forced the U-boat to the surface, and its crew abandoned the ship near Port Said. A team from Petard boarded the sinking submarine.

A complete four-wheel Enigma machine and some TRITON code books and documents were left behind by the Germans. The British were able to capture the code books and return them to Petard. The submarine sank quickly, taking the Enigma and two British seamen who attempted to extract it to the bottom. With the information recovered by Petard, the British were able to crack the remainder of the TRITON code, and were made aware of the operations controlled by Doenitz. It allowed the British and Americans to be ready and waiting when the U-boats made an appearance.

The Crucial Battle of the Atlantic During World War II
Survivors from a sunken U-boat awaiting rescue by an Allied ship. Imperial War Museum

22. The code breakers were blinded again in early 1943

In early 1943, the number of U-boats operating in the Atlantic again threatened to overwhelm the convoy escorts, in part because the Germans made changes to TRITON. For over a week, the British codebreakers at Bletchley Park had no information about Doenitz’s plans. In March, 1943, over 475,000 tons of Allied shipping went down in the Atlantic, in 82 ships. In the Indian Ocean, the Caribbean, and the Pacific, another 38 ships were lost to U-boats. The Allies destroyed 12 German submarines in return.

The following month the tide turned against the Germans. U-boat losses mounted. Through April the Germans sank 39 Allied ships, totaling 235,000 tons. But many more ships got through, resupplying the nearly desperate British. 15 U-boats were lost as the Allies refined their tactics using newly developed weapons. The American shipbuilding program produced more and more destroyer escorts and destroyers, as well as long-range bombers and flying boats. Escort carriers surrounded by a task force developed specifically for anti-submarine warfare actively hunted the Germans.

The Crucial Battle of the Atlantic During World War II
The escorted convoy system led to the defeat of the U-boat threat by early 1944. Wikimedia

23. Black May broke the back of the German U-boat fleet

May, 1943, was the month in which the Allied Navies effectively defeated the U-boat threat. At the end of April and through the first week of May, a slow convoy of 43 ships and seven escorts was attacked by more than 30 U-boats. The allies lost 13 ships to the U-boat attacks which continued for week, but most of the attacks were unsuccessful. The combination of aerial observation and attack, depth charges, hedgehogs, and surface gunfire proved deadly for the Germans. The 13 ships sunk (63,000 tons) cost Doenitz 6 U-boats, with another 7 returned to port too damaged to rejoin the fight for some time.

During the month of May, in all actions, 43 U-boats were destroyed, 34 of them in the Atlantic. The same number of Allied ships were lost in the Atlantic, 34 ships. It was a loss of 135,000 tons, but it cost the Germans a full quarter of the available U-boat fleet. Doenitz withdrew his remaining boats from the North Atlantic, accepting defeat. German U-boat activity continued through the remainder of the war, but the concerted effort to defeat Great Britain by choking off its supplies was over. The Allies did not yet know it, but they had won the Battle of the Atlantic.

The Crucial Battle of the Atlantic During World War II
German prisoners from U-873 arrived at Portsmouth, New Hampshire, in 1945. US Navy

24. The U-boats were driven out of the South Atlantic the same year

The defense of the convoys in the South Atlantic was coordinated by the United States Navy and the small but effective Brazilian Navy and Air Force. The Brazilians escorted more than 600 convoys during the war, with a loss rate of 0.1%. More than 16,000,000 tons of supplies and equipment reached their destination safely under Brazilian escort, though submarine attacks by the Germans and Italians were common. American and Brazilian long-range aircraft, mostly B-24 Liberators, attacked enemy U-boats and reported their positions to surface ships which drove them off or destroyed them.

The Italians and the Germans both lost submarines in the waters patrolled by the Brazilians, who had entered the war partly in response to U-boats’ sinking ships off their coast. Between January and September 1943, German U-boats were sunk at a rate of more than one per month in Brazilian waters. For the Germans, they were irreplaceable by that stage of the war. The Allied bombing of German industries made construction of newer and more effective submarines difficult. In September, 1943, Doenitz launched a final attempt to defeat the Allies in the North Atlantic with U-boats. They sank 14 Allied ships (six of them warships) at a cost of 39 U-boats.

The Crucial Battle of the Atlantic During World War II
A war poster encouraging production for suppliers of the shipbuilding industry. National Archives

25. The costs of the Battle of the Atlantic were staggering

German U-boat activity continued through the end of the war, but the Battle of the Atlantic was won by January, 1944. When the war ended and the remainder of the U-boat fleet surrendered, the total was added up. 783 U-boats were destroyed (or captured) and 30,000 German sailors killed, 75% of the total U-boat fleet personnel. Germany also lost 4 battleships, 9 cruisers, and more than two dozen destroyers. The Germans sank 175 Allied warships. The damage inflicted on the Allies’ merchant fleets was brutal. Over 6,000 Allied freighters and tankers were lost. They took with them the lives of more than 72,000 seamen. Over 36,000 of them were civilian merchant seamen from all over the world.

Had the Allies not prevailed in the Battle of the Atlantic, the great buildup of arms and men in Great Britain for Operation Overlord could not have been achieved. The total losses in terms of tonnage was over 21 million tons, all of it sent to the bottom of the ocean, where most of it remains. The ships were replaced by over 38 million tons of new shipping, most of which was built in the United States, at enormous costs. Though historians dispute how close Germany came to winning the Battle of the Atlantic, there is little dispute over its cost in lives and materiel for all of the contending nations.


Where do we find this stuff? Here are our sources:

“Escort of Convoy: Still the Only Way”. R. A. Bowling, Proceedings, United States Naval Institute. December, 1969

“Battle of the Atlantic”. Bernard Ireland. 2003

“The Battle of the Atlantic”. Donald Macintyre. 1961

“The Atlantic Campaign”. Dan van der Vat. 1988

“Ten Years and Twenty Days”. Karl Doenitz. 1959

“Wolf Packs”. Ivano Massari, War History Online. April 25, 2018

“The Italian Submarine Base in Bordeaux, France”. Christiano D’Adamo. Regia Marina Italiana. Online

“The Nazi Marauder”. Jon Guttman, History Net. Online

“Escort: The Battle of the Atlantic”. D. A. Rayner.

“Visiting Bismarck: Explorers Revise Its Story”. William J. Broad, The New York Times. December 3, 2002

“Battleship Bismarck: A Survivor’s Story”. Burkhard von Müllenheim-Rechberg. 1980

“The Real Cruel Sea: The Merchant Navy in the Battle of the Atlantic”. Richard Woodman. 2004

“U-boat Assault on America: Why the US was Unprepared for War in the Atlantic”. Ken Brown, US Naval Institute.

“The Defeat of the German U-boats: The Battle of the Atlantic”. David Syrett. 1994

“Business in Great Waters”. John Terraine.1987

“The Brazilian Navy in World War II”. Homer C. Votaw. 1950

“The Battle of the Atlantic”. Samuel Eliot Morison. 1947

“Galloping Ghosts of the Brazilian Coast”. Alan C. Carey. 2004

“All Hell Let Loose: The World at War, 1939-1945”. Max Hastings. 2012