Text and web-site by James Bowen

The Battle of the Atlantic opened on 3 September 1939 with the sinking by a German U-boat of the ocean liner Athenia off the Irish coast and lasted until the surrender of Germany in May 1945. It was one of the three most important battles of World War II because, until the tide of this battle began to turn against Nazi Germany in mid-1943, the fate of Britain hung in the balance and the Allied strategic plans for liberation of Nazi-occupied Europe could not be put into operation.

Allied tankers were priority targets for German submarines during the Battle of the Atlantic in World War II because Britain could not
survive without imported oil. This photograph depicts the Allied tanker Dixie Arrow torpedoed by the German submarine U-71 in 1942.

Nazi Germany turns to submarine warfare after failing to win the Battle of Britain in 1940

When the Battle of Britain demonstrated that the Luftwaffe’s bombing could not force a British surrender, the Germans resolved to deploy their navy to strangle the sea lifelines that were vital to Britain’s survival. This German strategy greatly intensified the Battle of the Atlantic and produced a grave threat to the survival of Britain.

The main weapon used by Nazi Germany in the Battle of the Atlantic was the submarine, commonly known as the U-boat. The primary Allied defence against the German U-boat was to move merchant ships across the Atlantic in convoys protected by escorting warships.

When France fell, German U-boats were able to operate from bases on the French Atlantic coast. The U-boats could now operate closer to the transatlantic convoy routes and stay out of range of British land-based anti-submarine aircraft. German Condor long-range bombers based in France joined the U-boats in a concerted assault on Allied shipping. Convoy losses began to rise sharply, and what had been a clash between two powerful adversaries then became a battle for Britain’s survival.

The Germans had two main aims in their conduct of this very lengthy battle. The first was to force the surrender of Britain to Germany by cutting off the supply of food and the materials required by the British to continue the war against Nazi Germany, including oil. The second aim was to isolate the United States from Europe and prevent it fulfilling its self-appointed role as "the arsenal of democracy". If the flow of American weapons to Russia and to British and Australian forces in North Africa, the Mediterranean, and the Middle East could be halted by German submarines, then the balance would swing in favour of Nazi Germany in those areas of combat.

As a counter to the U-boat menace, the British purchased long-range Catalina PBY patrol seaplanes from the United States in May 1941; developed longer-range escort warships; and added more sophisticated radar to their primary anti-submarine underwater detection device called ASDIC (Americans refer to it as Sonar). Although still officially neutral, the United States assisted Britain by providing escorts for American merchant ships on the transatlantic crossing.

An SB2U Vindicator bomber from the USS Ranger (CV-4) flies anti-submarine patrol over a convoy en route to Cape Town on 27 November 1941. At this time,
the Japanese had not yet launched their devastating sneak attack on the US Pacific Fleet at Pearl Harbor and Germany had not yet declared war on the United States.

In September 1941, the Germans introduced the "wolf pack" strategy that involved one U-boat shadowing a convoy and radioing its location, course, and speed to U-boat headquarters so that other U-boats could be directed to converge on the convoy. When the wolf pack had assembled, the U-boats would wait for nightfall and then launch a massive assault that was intended to overwhelm the escorting warships. To counter the wolf pack menace, the British developed small escort carriers equipped with anti-submarine patrol planes and fitted escort warships with radio direction-finders that enabled them to pinpoint the location of the shadowing U-boat and its radio transmissions.

The Battle of the Atlantic strained even America's vast resources

Americans entered the Battle of the Atlantic officially on 11 December 1941 when, following Pearl Harbor, Germany and Italy declared war on the United States.

Initially, the American involvement in the Battle of the Atlantic was disastrous. During two decades of peace and isolationism, the Americans had neglected to develop sophisticated anti-submarine tactics of the kind developed by the British, for whom it was a matter of national survival. The Americans were not familiar with the use of convoys protected by escort warships. The U-boats quickly discovered a killing ground in American waters and sank 675,000 tons of American shipping in the first three months of 1942. However, the Americans learned quickly. They borrowed ninety-five escort warships from the British and Canadians, adopted the convoy system, and undertook a massive building program of 1,000 escort warships of various kinds, including escort carriers.

Until mid-1943, the Germans were sinking merchant ships as fast as the Allies could build them and building submarines faster than the Allies could sink them. The inescapable conclusion from these grim facts was that Nazi Germany was winning the Battle of the Atlantic. During 1942, and the first half of 1943, even the resources of an industrial giant such as the United States were severely strained by the heavy losses of ships and their vital cargoes to German submarines.

Between June 1940 and June 1943, any significant diversion of Allied resources from the Battle of the Atlantic was capable of producing an Allied defeat in Europe, in the sense that Britain could have been rendered incapable of continuing the war. Since 1940, the British had been providing convoys and escorts across the Atlantic and to the Mediterranean theatre where the British and Australians were fighting the Germans, the Italians, and the Vichy French. In 1941, the British began supplying the Russians with war equipment to fight the German invasion of the Soviet Union, and the convoys to Russia faced appalling weather conditions and constant attacks by German submarines and aircraft operating from occupied Norway. The heavy drain on British resources constantly brought Britain close to breaking point. The diversion of a large number of escort warships from Atlantic convoy duty to protect the American amphibious landing in North Africa (Operation Torch) in November 1942 caused an alarming escalation in Allied convoy losses in the North Atlantic.

A German U-Boat under air attack during the Battle of the Atlantic. Photograph courtesy of the Australian War Memorial.

At this point, it is appropriate to question the potential impact on the Battle of the Atlantic of an American defeat at the Battle of Midway in June 1942. If America had suffered a major defeat at Midway, President Roosevelt would have come under enormous public and political pressure to divert significant resources to combating Japan in the Pacific. There is a very real possibility that a significant switch of American resources from the Atlantic to the Pacific could have led to Britain’s defeat by the U-boats, and consequently, an Allied defeat in the European theatre.

The loss of shipping from U-boats in the Battle of the Atlantic was so high in the second half of 1942, that Roosevelt and Churchill agreed that the Allies could not afford to pursue long-term objectives, such as the liberation of Europe, until the U-boat menace was brought under control. At the Casablanca Conference in January 1943, the Allied leaders agreed that top priority had to be given to defeating the U-boats.

Allied shipping losses reached the appalling level of 693,389 tons in the month of March 1943 when improving weather conditions made the work of the U-boats easier. On any given day, there were as many as one hundred U-boats at sea in the Atlantic, and their numbers enabled them to swamp the protecting escort warships. However, just when it appeared that the U-boats were winning the Battle of the Atlantic, the tide began to turn against them in April 1943.

The tide begins to turn against the U-Boats

Three important factors finally turned the tide against the U-boats: the Atlantic escort warships diverted to protect the American invasion of North Africa in November 1942 were returned to Atlantic convoy service; increasing numbers of American escort warships came into service; and escort warships were armed with increasingly sophisticated anti-submarine weapons or equipped with anti-submarine patrol aircraft. All of these factors combined to produce the sinking of forty-one U-boats in the month of May 1943. The losses in May were so heavy that Admiral Donitz was forced to order a temporary withdrawal of U-boats from the North Atlantic to enable U-Boat headquarters to rethink tactics. It was the turning point of the Battle of the Atlantic. Although the U-boats never again reached the peak of their successes in March 1943, they remained a menace to Allied shipping in the Atlantic until the end of the war in Europe.

The Hedgehog anti-submarine mortar played an important role in defeating the German U-Boats in the Battle of the Atlantic. The Hedgehog fired 24 contact-fused bombs ahead of the attacking warship. Depth charges exploded at pre-determined depths behind the attacking warship without necessarily contacting the hull of the submarine, and the massive turbulance created by the explosion made it difficult to continue tracking the submarine with sonar. Hedgehog bombs avoided this problem because they exploded only on contact with the submarine. This Hedgehog is mounted on the forecastle of the destroyer HMS Westcott.

To appreciate the seriousness of Allied shipping losses in the Battle of the Atlantic, and how close the Allies came to defeat in Europe, it is necessary to look at the appalling statistics of shipping losses. The Allies lost 2,282 convoyed ships sunk, totalling 14.4 million gross tons. If the tide had not turned against the U-boats in 1943, it is by no means improbable that the British would eventually have been starved into submission to Germany. The whole of Africa and the Middle East would almost certainly then have come under the control of Germany and Italy. In these circumstances, the final outcome of the war in Europe between the Germans and Russians would be difficult to assess.

The United States would not have been defeated if the Allies had lost the Battle of the Atlantic, but it would have become isolated in the Americas and would have lacked a springboard from which to launch an invasion to liberate Europe.

After weighing all of these factors, I have ranked the Battle of the Atlantic second in the pivotal battles of World War 2 after the Battle of Britain.

James Bowen

17 June 2005