The Battle of the Atlantic explained

Voiceover: "In the spring of 1941, Britain was in the midst of an Atlantic crisis. German submarine, surface and air attacks were sinking merchant ships by the hundred. If losses continued, Britain could lose a quarter of its fleet within the year and might just be starved out of the war. Yet just a few years later, everything had changed. By 1943, German U-boats had gone from predator to prey, as the Allies took full control of Atlantic Ocean. So how did they do it? 

Robert Rumble, IWM curator: "The Battle of the Atlantic was a race of advanced technology. Skilled German U-Boat captains, coordinated by the famous Enigma system, hunted down British ships often at will. The Royal Navy needed to step up. Innovations in escort vessels, Sonar and Radar, and British aircraft, were vital to defeat the U-Boat menace. This is the story of the race to victory in the Battle of the Atlantic.

Throughout the war, German U-Boats would sink millions of tons of shipping, especially along the crucial North America route in the North Atlantic. In the display behind me, each ship represents five allied vessels that were sunk or damaged by German submarines. It is a visual representation of the enormity of Allied losses in the Atlantic. June 1942 was the worst month for the Allies with the loss of 830,000 tons of shipping. But we can see that by 1943, this number had dropped significantly."  

Voiceover: "Before the Second World War Britain was one the world’s great powers. It had a sprawling empire and the world’s largest navy. However, Britain also had a major weakness. As an island nation, Britain relied on merchant ships for crucial supplies, almost all of which had to pass through the Atlantic. The German Navy understood that breaking this chain had the potential to cripple Britain and their war effort. And whilst the German surface fleet was small, their submarines were some of the most advanced in the world."  

Robert Rumble: "On the eve of war in 1939, the German Navy were prepared to fight a ‘war of attrition’ against the British. German Admirals Erich Raeder, Head of Naval Command, and Karl Dönitz, commander of the U-boat arm, had come of age during the ‘unrestricted’ submarine warfare of the First World War. Despite Adolf Hitler’s wish for a short, quick war, Raeder understood this would be a total war. Although Hitler aspired to a grand surface fleet to rival the Royal Navy, Dönitz thought resources should be focussed on submarines to destroy Britain’s merchant fleet. In this war of attrition, Dönitz considered every enemy ship a legitimate target."

Voiceover: "Germany began the Battle of the Atlantic with two key weapons. The Mark VII and Mark IX U-boats. The Mark VII medium range submarine was the workhorse of the German Navy. With 14 compressed air or electric torpedoes, and an operational range of 6,500 miles, nearly seven hundred of these formidable submarines were built during the Second World War. The larger and more powerful Mark IX U-boat was armed with 22 torpedoes, and had a global range to fight anywhere in the world. Able to sneak up on an enemy ship, underwater, undetected, before unleashing a devastating volley of torpedoes, both U-Boats were a truly terrifying prospect to Allied sailors, but they weren’t completely invincible."  

Robert Rumble: "This massive aircraft is the Short Sunderland flying boat. They were introduced by the Royal Air Force Coastal Command in 1938, a year prior to the outbreak of the Second World War. The Sunderland is a long-range maritime patrol aircraft, designed to operate at sea. It flew as a convoy escort, as an anti-submarine and shipping aircraft, and for search and rescue. The Sunderland would prove to be one of the key weapons of the Battle of the Atlantic. Key to the defence of British merchant shipping was to group ships in convoy, escorted by long range aircraft and small anti-submarine ‘escort’ vessels. The Atlantic covers over 100 million square kilometres. In such a vast space, finding a convoy was harder than finding a single ship, as there were fewer targets, and attacking U-boats could be attacked by the escorting warships."  

Voiceover: "At the beginning of the war, the British attempted to hem the German U-boats in and stop them reaching the Atlantic. Allied vessels blockaded German ports while RAF Coastal Command patrolled the English Channel and the North Sea. But despite these defences, on the 3rd of September 1939, the SS Athenia – a British passenger liner - became the first Allied ship to be sunk in the Atlantic by a German U-boat. This marked the beginning of the Battle of the Atlantic. From September 1939 to May 1940, over 300 Allied ships were sunk in the Atlantic, to only 24 U-boats lost. And things were about to get even worse."

Film footage narrator: "The conquering armies now stood on the shores of the Atlantic." 

Voiceover: "France had fallen and Germany now had direct access to the Atlantic along the French west coast. German U-boats could now attack convoys even further away and spend much more time at sea than before. This had a devastating impact on Allied shipping, and immense losses continued through to early 1941. Among German submariners, this period would become known as the ‘First Happy Time’. Meanwhile, Britain had lost a huge amount of military equipment in France and was becoming increasingly depended on American Lend Lease support, which made the Battle of the Atlantic an even more important theatre of the war. But it was a battle the British were losing. They could only build 1.25m tons of shipping each year, but if the losses for March and April 1941 continued, they were set to lose 7.3m tons by the end of the year. A solution was needed and fast."  

Robert Rumble: "Asdic, later known as sonar, was a secret device for locating submerged submarines by using sound waves. It consisted of an electronic sound transmitter and receiver. This was housed in a metal dome beneath the ship's hull. High-frequency soundwaves were sent out and bounced back as audible pings when they hit a submarine. This stopwatch was used to time the pings heard when a U-boat was detected by Asdic. The number of seconds between pings corresponds to a distance shown on the stopwatch, and the pitch of the echo revealed if it was approaching or moving away."  

Film footage narrator: "That sound on the Asdic detected the engines of a submarine. Definitely a sub, sir. Quite close to us. That's it, keep after it. Swing right over and start blasting. There goes the underwater blast."

Robert Rumble: "Despite these advantages, a highly trained operator was required to use the equipment effectively, and even then, the system initially proved useless when U-boats attacked on the surface at night. However, as the war progressed, the technology improved, making Asdic easier to use and improving its success rate. The feared U-boats had now lost their most important weapon – the element of surprise."

Voiceover: "By March 1941, the campaign had become a focal point of the entire war. Churchill publicly named the campaign ‘The Battle of the Atlantic’ and created a new War Cabinet sub-committee to address the issues with the losses in shipping. Meanwhile, the Royal Navy began to bring in extra maritime patrol aircraft." 

Robert Rumble: "These were fitted with long-range radar, to detect any U-boats operating on the surface, as well as automatic machine guns, bombs and depth charges to destroy them. British aircraft such as the Short Sunderland, were used alongside US built aircraft including the Lockheed Hudson, Consolidated Catalina flying boat, and the Consolidated Liberator." 

Voiceover: "Along with new Coastal Command bases, including one in Iceland, these pushed the U-boats into an area where Allied aircraft could not reach them, this ‘mid-Atlantic gap’ was effectively a safe zone for the U-boats, and became known as ‘the black pit’ to Atlantic convoys."  

Robert Rumble: "The posters on display here were used to remind the British public of the importance of the battle going on in the Atlantic, whilst in Germany, aerial propaganda leaflets such as these were dropped by the Allies. They show U-boat service leading to a cold grave – and they weren’t wrong, once a U-boat was sunk the chances of survival for its crew were incredibly slim."  

Voiceover: "In May 1941, the Royal Navy successfully sank the German Battleship Bismarck after a prolonged chase the night before. British ships rescued 110 survivors but had to withdraw due to a U-boat sighting. This left hundreds more German sailors to their fate. The sinking of the Bismarck was an enormous blow to German morale, and for Hitler it validated his fears of facing the Royal Navy in open warfare. But for the British, the sinking, combined with an increase in escort vessels and the growing effectiveness of RAF Coastal Command, gave the second half of 1941 a much more positive outlook. But that optimism would be short lived. In December 1941 the United States joined the war, and the Kriegsmarine immediately dispatched U-boats to the Americas." 

Film footage narrator: "The Germans opened unrestricted submarine warfare."

Voiceover: "The US were not yet ready to deal with U-boats and what followed was an open season on Allied shipping from the East coast to the Caribbean. This was the ‘Second Happy Time’ between January and August 1942. 868 ships totalling 3.1 million tons of shipping were lost, against only 42 German U-Boats.  

Back in Britain, the Admiralty were pushing for an increased allocation of long-range aircraft, but despite the skyrocketing losses in shipping, Churchill rejected these proposals. He thought it was more important to take the fight directly to Germany, and build up the RAF’s bomber force instead. American shipbuilding efforts were beginning to increase, and Churchill believed they would soon be producing enough ships to replace British losses. This would soon be proven not to be the case. By now the United States had managed to set up several new air bases in South America, the Caribbean and Greenland, forcing the U-boats to return to the familiar hunting grounds of the mid-Atlantic gap. It was here that the tide of the battle began to turn." 

Robert Rumble: "By 1943 Allied countermeasures were beginning to take their toll. That year 284 U-boats were sunk, in comparison to only 27 in 1940. The Germans developed new countermeasures of their own to try and stay in the game. Technology such as ‘BOLD’ decoys, which confused British Asdic systems, ‘Alberich’ anti-sonar coating, which reduced Asdic effectiveness, and the schnorkel which allowed U-boats to stay submerged for longer. U-boats were powered by diesel-electric engines, which required them to remain on the surface for long periods, drawing in air for the diesel engines. When submerged, they operated by battery power, but this only had a short range. ‘Schnorkel’ was a long-extended pipe to the surface, that could draw down air for the diesel engines when submerged. However, all of these innovations had limited effectiveness when set against experienced British Asdic operators, or when operating at a reduced depth due to the limitations of the ‘Schnorkel’ device."

Voiceover: "Erich Raeder resigned as Commander in chief of the German Navy in January 1943 and was replaced by Karl Dönitz. The German Submarine fleet reached its peak in early 1943, with around 240 U-boats in operation and more than 100 of those out to sea at any one time. But this was also a key turning point for the Allies, who cracked the Enigma code at the end of 1942. Now able to intercept and decipher German messages, the Allies were able to divert convoys away from U-boat wolfpacks, whilst going on the offensive to hunt down U-boats in their known locations. RAF Coastal Command also began launching a series of attacks into the Bay of Biscay from February 1943. The idea was to destroy German U-boats leaving France before they could reach the Atlantic. The effectiveness of these missions is up for debate. Coastal Command suffered significant losses because the bay was in range of Luftwaffe fighters. But the missions did successfully put additional pressure on German U-boats. The final piece of the puzzle that turned the tide in the Atlantic were Allied advancements in aircraft and weapons technology."

Robert Rumble: "The Liberator was of particular importance as they were able to plug the ‘Mid-Atlantic air gap, when the ‘Very Long-Range’ variant was introduced in May 1943. This was a variant of the B24 Liberator strategic bomber, similar to this aircraft on display at IWM Duxford. This particular aircraft was manufactured by the Ford Motor company in Detroit in March 1945. Liberators were the most heavily produced aircraft of the Second World War, with over 19,000 built in the US, and serving with the USAAF, US Navy, RAF and Allied air forces around the world. The final nail in the coffin for German U-boats was the introduction of the British ‘Hedgehog’ and ‘Squid’ devices in 1943. The ‘Squid’ fired a salvo of three-six large 12-inch mortar bombs over its target. A direct hit would almost always sink a U-boat. The "Hedgehog", like the one on display behind me, was a mortar which could fire a salvo of 24 bombs in a circular pattern ahead of the ship. This system was much more accurate than stern deployed depth charges and covered a wider area of damage."  

Voiceover: "The Atlantic Gap was now effectively closed by Allied Aircraft, and escort vessels were armed with the tools to reliably defend against attacking wolfpacks. Things got even worse for the Kriegsmarine when Portugal offered an airbase in the Azores to the Allies, further increasing their command over the Atlantic. Black May of 1943, saw 34 U-boats sunk and so, on the 24th, Karl Donitz decided to call his forces back. They would return to the ocean, but their impact would never be the same." 

Robert Rumble: "By summer 1943, the combination of advanced escort vessels, Asdic and Sonar, long-range patrol aircraft, and weapons such as Hedgehog and Squid, had finally defeated the U-boat threat. The vital sea lanes between Britain and North America were now fully open. This was to prove crucial for the D-Day invasion, and the liberation of Europe over the next two years. The U-boat threat wasn’t entirely diminished. By 1945 the German Navy had developed the advanced, fully submergible, Type XXI ‘Electro-boat’. But it was all too little, too late."

Voiceover: "Over 1,300 Allied ships were sunk in the Atlantic in 1942, but that number more than halved in 1943, and halved again in 1944. 241 U-Boats were sunk in 1943, more than all previous years combined, and those numbers would continue to the end of the war. The Battle of the Atlantic was the longest campaign of the Second World War, running continuously from the first days, right up until the defeat of Nazi Germany six years later. 3 out of every 5 German Submariners would die over the course of the war, along with many more sailors, merchants, and civilians in this most decisive of battles."