The Battle of the Atlantic: The longest military campaign of WWII
U-Boat Wargamers tells the story of the Women's Royal Naval Service (WRNS) who helped take down Germany's fearsome U-boats. The show airs Tuesdays at 9pm on Sky HISTORY.
At 7:30pm on 3rd September 1939, a torpedo fired from a German submarine slammed into the hull of the British ocean liner SS Athenia. Fourteen hours later, Athenia sank beneath the waves. 118 passengers and crew went down with her. The ocean was now a hunting ground. The Battle of the Atlantic had begun.
Athenia was attacked within hours of Britain declaring war on Germany. The sinking of the liner marked the beginning of the longest, continuous military campaign of the Second World War. The battle was a cat-and-mouse game between merchant and navy ships of the Allies and the German Kriegsmarine - in particular its fearsome U-boats. The first shot was fired on the very first day of the war; the last was mere hours before Germany surrendered. At stake was not just the survival of Great Britain, but the whole of Western Europe.
The United Kingdom was a hard nut to crack. As an island, a successful invasion from the sea first required the German Luftwaffe to gain air superiority over the RAF - something that proved impossible after the Battle of Britain. The country did, however, have an Achilles heel - its reliance on imports of raw materials and food. From the very start of the war, Britain organised its trans-Atlantic merchant ships into convoys. It was these convoys that Germany needed to target if it was to knock the UK out of the war. In its U-boat fleet, the Kriegsmarine had the perfect tool for the job.
The Wolf Packs
Germany’s Admiral Karl Dönitz, commander of the Kriegsmarine’s U-boat arm, submitted a plan to the head of the navy, Grand Admiral Erich Raeder, to target British convoys using a tactic known as the ‘Wolf Pack’. This involved several U-boats converging on a convoy and attacking it en masse, usually after drawing away its escorts with a couple of submarines acting as decoys. Dönitz told Raeder that he believed a fleet of 300 large ‘Type VII’ U-boats harassing and sinking British shipping would be enough to force the UK out of the war.
To begin with, the Wolf Packs were incredibly successful, so much so that Churchill later wrote: ‘The only thing that ever really frightened me during the war was the U-boat peril.’
The tactic was first deployed in September 1940 when four U-boats attacked a convoy of 42 ships, sinking eleven of them. The following month, a convoy of 35 merchant ships and six escorts was attacked; 20 of the ships were sunk with the loss of 141 lives. The following day, a pack attacked a 50-strong convoy with an eleven-ship Royal Navy warship escort, sinking twelve merchantmen. The Wolf Pack escaped without a scratch. In December, thirteen ships from a 41-ship convoy were lost. As ship after ship sank to the bottom of the Atlantic Ocean, the delighted Germans nicknamed this period the ‘Happy Time’.
Beefing up the convoys
After initially dismissing the importance of escorts with disastrous consequences, the Admiralty realised it had to increase its support for the convoys. Out went the idea of abandoning the convoys to hunt for U-boats which had almost lost the navy HMS Ark Royal, and in came permanent escorts of destroyers and corvettes, along with a huge expansion of the Royal Canadian Navy, which went on to shoulder a lot of the escorting burden. These escorts were ordered to stay with the convoys and fend off the submarines when they attacked.
The tactic paid off. By March 1941, three U-boats had been sunk with the loss of three of Dönitz’s best captains. In response, the U-boats were ordered further west to attack the convoys before their escorts could join them. Ten merchant ships were hit and sunk as a result. In response, the Admiralty decided to provide escorts for the full length of the convoys’ crossings.
America enters the war
America’s entry into the war in December 1941 saw the formation of the Mid-Ocean Escort, a joint British-Canadian-US naval operation of cruisers and destroyers that protected the convoys from attack until 1943. After that, the US withdrew its ships to concentrate on protecting the ‘CU’ and ‘GU’ convoys that carried vital supplies of fuel, food and ammunition to the UK and Gibraltar for the European, Mediterranean and North African campaigns.
The US also threw long-range bombers and flying boats into the fight, both of which were capable of spotting and attacking U-boats and relaying their positions to Allied vessels. Meanwhile, the British continued to develop technological solutions to the U-boat menace, most notably refining the high-frequency direction finder (HF/DF) which could locate submarines. This was done by picking up the enormous amount of radio chatter that was required by the Germans to coordinate their attacks. It is estimated that 24% of the U-boats sunk in the war were located by HF/DF.
Cracking the Enigma code
To keep their orders secret, the Germans developed an encryption machine called Enigma that turned their messages into incomprehensible code. Thanks to the successful recovery of Enigma material by the destroyer HMS Bulldog in May 1941, the Allies were able to decode Axis messages, as well as gain vital insight into how the machine worked. This allowed the Allies to locate U-boat packs and steer their convoys around them, resulting in a drop in the loss of merchant ships and their escorts.
The Germans switched to an updated machine in 1942, making their messages unreadable once more and attacks on convoys increased as a result. However, the capture of more Enigma material allowed Alan Turing and his team of codebreakers at Bletchley Park to crack Germany’s new Enigma and attacks on convoys once again dropped. The Allies were able to read Enigma messages and orders for the rest of the war.
While Dönitz was suspicious that Enigma had been compromised, he was persuaded that direction-finding technology lay behind the Allies’ ability to detect and avoid Wolf Packs.
Advances in technology, the loss of German naval bases in previously conquered countries, the efforts of the codebreakers and the sheer weight of numbers of ships and planes that the Allies could throw into the conflict, led to the defeat of the Axis in the Battle of the Atlantic. The introduction of long-range Liberator bombers and an increase in aircraft carriers amongst the escort groups meant nowhere in the ocean was safe from air attacks.
The construction and deployment of US destroyer escorts meant that the convoys could be protected throughout their journeys by fast, manoeuvrable ships that also worked as highly effective U-boat hunter-killers. For the last two years of the war, Germany was reduced to attacking shipping around British coastal waters. The ‘Happy Time’ of the Wolf Packs striking fear into the merchant seamen of the Atlantic was a distant memory.
The final actions of the battle took place on the 7th and 8th May 1945. U-320 was the last U-boat to be sunk; a Norwegian minesweeper and two freighters were the final losses on the Allied side. Following Germany’s surrender on 7th May, its 174 remaining U-boats were handed over to the Allies. The vast majority were scuttled in 1946. The Battle of the Atlantic, the longest conflict of the war, was finally over.
Facts about the Battle of the Atlantic
- Germany lost 783 U-boats in the battle and 30,000 submariners. Italy deployed 32 submarines to the Atlantic, seventeen of which were lost along with around 500 crew.
- On the Allied side, 3,500 merchant ships were sunk during the battle, along with 175 warships. 36,200 naval personnel and 36,000 merchant seamen lost their lives.
- Germany conducted a limited surface war for the first few years of the war. However, the loss of the gigantic battleship Bismarck after it attacked and sank the battlecruiser HMS Hood helped persuade the Germans to concentrate on submarine warfare for the rest of the conflict.
- Karl Dönitz became President of Germany after Hitler’s suicide. He was imprisoned for ten years in Spandau Prison in West Berlin. Unrepentant about his role in the war and his support for Hitler, he died of a heart attack in 1980.