20 Facts About the Battle of the Atlantic in World War Two

Graham Land

7 mins

09 Aug 2018

A significant portion of the Second World War was fought and decided on the high seas. At the start of the conflict the Royal Navy was the largest in the world, though it suffered huge losses early on. The Battle of the Atlantic was the longest lasting continuous campaign of the entire war.

From 1941 the United States Navy saw significant growth and provided much needed support against German and Italian naval forces, as well as playing the central role in the Pacific war against Japan.

Here are 10 facts about British Naval engagement with the Germans in the Atlantic during World War Two.

1. The Battle of the Atlantic began on the first day of the war


The opening months of the Second World War are commonly referred to as the Phoney War but there was nothing phoney about the war in the Atlantic, which began on the very first day.

The first British ship to be sunk was the SS Athenia, a transatlantic liner torpedoed by a U-Boat off the coast of Ireland on 3 September.

Oberleutnant Fritz-Julius Lemp fired on an unarmed vessel, without warning, in violation of the Hague Conventions. More than 100 of the 1400 souls on board were killed.

2. The first battle was fought off the coast of South America 

Shortly after the outbreak of war, the Royal Navy dispatched a force to hunt down the German pocket battleship Graf Spee. Under the command of Hans Langsdorff, by November 1939, the Graf Spee had already sunk eight merchant vessels in the Atlantic.

Commodore Henry Harwood intercepted Langsdorff at the mouth of the River Plate. Harwood’s force, constituting the heavy cruiser HMS Exeter, and light cruisers Ajax and Achilles, exchanged blows with the German pocket battleship. Badly damaged, the Graf Spee broke off the action and made for the port of Montevideo in neutral Uruguay.

Restrictions placed on vessels making use of neutral ports dictated that Graf Spee could only remain in Montevideo for as long as it took to make vital repairs. All Harwood needed to do was wait.

In the meantime, the Royal Navy spread rumours that Harwood was amassing a huge fleet off Montevideo. When Langsdorff finally departed the port, he did so in the belief that a vast armada was waiting for him. An armada that included the British carrier, Ark Royal. In reality, reinforcements had not arrived.

Believing they faced annihilation, on 17 December, Langsdorff ordered his crew to scuttle the ship. With his crew disembarked, Langsdorff went ashore, wrapped himself in the flag of the German navy, and shot himself.

The Admiral Graf Spee in Montevideo harbour, displaying damage inflicted during its battle with Harwood’s force

3. Britain lost its first submarine to friendly fire on 10 September 1939


HMS Oxley was mistakenly identified as a U-boat by HMS Triton. The first U-boat was sunk four days later.

4. Britain employed the convoy system from the start of the war

The Royal Navy employed the convoy system to protect merchant shipping in the Atlantic during the First World War and reinstated the practice as soon as the Second World War began. Convoys grouped merchant vessels together so they could be protected by fewer escorts.

When America entered the war in 1942, they initially rejected the use of the convoy system for merchant shipping. As a result, U-Boats sank hundreds of Allied ships along the east coast of the United States in the opening months of 1942. The Germans referred to this as a “happy time”.

The success of the convoy system is clearly demonstrated by the fact that of 2,700 Allied and neutral merchant vessels sunk during by submarines the campaign, less than 30% were travelling in convoy.

5. 27 Royal Navy ships were sunk by U-boats in a single week in autumn 1940


6. Britain had lost over 2,000,000 gross tons of merchant shipping before the end of 1940


7. Otto Kretschmer was the most prolific U-Boat commander


Between September 1939 and March 1941, Kretschmer sank more than 200,000 tones of shipping. He was known as Silent Otto due to his insistence on radio silence but he also gained a reputation for treating stricken crews with compassion. His Second World War career came to an end in March 1941 when he was forced to the surface by two Royal Navy escort vessels and he and his crew were taken prisoner. He remained a POW for the rest of the war and was eventually allowed to return to Germany in 1947.

8. Winston Churchill claimed he feared the U-Boats

In his memoirs, published after the war, Winston Churchill noted:


Whether this reflected his true feelings at the time, or was exaggerated for effect in the book, we cannot know.

9. Several key factors helped turn the tide against the U-Boats. Providing the convoys with air cover was key.

The B-24 Liberator enabled RAF Coastal Command to close the Mid Atlantic Gap

At the beginning of the war, a 500 mile gap existed in the middle of the Atlantic, which could not be covered by land-based aircraft. Since escort carriers were also scarce until later in the war, this meant the U-Boats practically had a free reign in this so-called “Black Pit”.

Responsibility for anti-submarine operations from land bases fell to the RAF’s Coastal Command. In 1939 Coastal Command was only equipped with short-range aircraft such as the Avro Anson, and flying boats such as the Sunderland. However by 1942 the RAF was receiving increasing numbers of the very long range B-24 Liberator, which helped to close the gap.

At sea, the Mid Atlantic Gap was patrolled by the Fleet Air Arm. Like Coastal Command, they started the war inadequately equipped for their perilous job. Central to improving this situation at sea was the delivery of escort carriers – either converted from merchant ships, or purpose built.

By mid 1943 the gap was closed and all Atlantic convoys could be provided with air cover.

10. The Allies developed technologies to detect the U-Boat

The Allies developed a raft of new and improved technologies to combat the U-Boat during the Battle of the Atlantic. Asdic (sonar), originally developed before the First World War, was improved to allow better detection.

The development of short wavelength radars allowed for the introduction of shipborne radar. And high-frequency direction-finding (Huff-Duff) allowed ships to locate U-Boats using their radio transmissions.


11. And new weapons to destroy them

When the Royal Navy went to war, their only anti-submarine weapon was a depth charge delivered from a surface vessel.

Over the course of the Battle of the Atlantic, the Allies developed air-depth bombs that enabled aircraft to attack U-Boats. They also developed new ways of launching depth charges from ships.

Hedgehog (and its successor Squid) was an ahead-throwing anti-submarine weapon that launched depth charges up to 300 yards in front of the ship. This system, introduced in late 1942, prevented the explosion from interfering with Asdic resulting in the ship losing track of the U-Boat.

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12. Canada played a crucial role

Canada declared war on Germany on 10 September 1939. At that time, the country’s navy amounted to 6 destroyers. Its primary role would be escorting convoys from Novia Scotia across the Atlantic.

To meet its responsibilities, Canada embarked on an ambitious ship building programme that ultimately employed 126,000 civilians and saw Canada emerge from the war with the world’s fourth largest navy.

13. May 1943 was a milestone

For the first time, more U-Boats were sunk than Allied merchant vessels.

14. German battleships flippantly seized an American transport ship on 3 October 1939


This early act helped to turn public favour in the US against neutrality and towards helping the Allies.

15. In September 1940 America gave Britain 50 destroyer ships in exchange for land rights for naval and air bases on British possessions

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These ships were of First World War age and specification, however.

16. American-built Liberty ships kept supplies flowing across the Atlantic

These simple utility vessels could be produced quickly and cheaply in order to replace shipping lost to U-Boats in the Atlantic. Over the course of the war, the United States produced more than 2,000 Liberty ships.

17. Roosevelt announced the establishment of the Pan-American Security Zone in the North and West Atlantic on 8 March 1941

It was part of the Lend-Lease Bill passed by Senate.


18. From March 1941 until the following February, codebreakers at Bletchley Park had great success


They managed to decipher German Naval Enigma codes. This made a significant impact in protecting shipping in the Atlantic.

19. The Bismarck, Germany’s famed warship, was decisively attacked on 27 May 1941


Fairey Swordfish bombers from the HMS Ark Royal aircraft carrier inflicted the damage. The ship was scuttled and 2,200 died, whilst only 110 survived.

20. Germany renewed the Naval Enigma machine and codes in February 1942.


These were finally broken by December, but could not be read consistently until August 1943.