A Campaign, Not a Single Battle
The Battle of the Atlantic is the name given to the struggle over the shipping routes of the North Atlantic during the Second World War. It lasted from September 1939 until May 1945 and had no single decisive day. Instead, it was a long contest of attack and counter-measure. Britain depended on imported food, fuel and raw materials, and later on supplies and troops from North America. If those ships could be stopped, Britain might be starved of war supplies. That is why the winner of the campaign mattered so much for the rest of the war.
The Lessons of 1917
The idea of grouping merchant ships under naval escort was not new. In the First World War, German submarine attacks on merchant shipping, which accelerated sharply in 1917, nearly brought Britain to a crisis. After debate within the Admiralty, convoys were introduced that year and losses fell. A convoy might appear to be an easier target, being a large group, but the ocean is large, and finding a convoy was difficult. Also, a group of ships with escorts could defend itself, whereas ships sailing alone could be picked off. The famous sinking of the Lusitania in 1915 had shown earlier how exposed unescorted liners were, as the Lusitania sinking had shown in 1915.
The First Years
In 1939 convoys were quickly organised again, with escorts from the Royal Navy and, increasingly, the Canadian navy and others. Early in the war, Germany had few submarines, but after the fall of France in 1940 it gained bases on the Atlantic coast, which extended their range. German U-boats, under Admiral Karl Dönitz, began operating in groups called wolf packs, which gathered around a convoy and attacked together, often at night and on the surface.
Escorts were often too few, ships too slow, and equipment limited. Merchant ship losses were severe in 1940 and 1941, and continued after the United States entered the war in December 1941, when U-boats attacked shipping off the American coast, where convoys had not yet been fully adopted. The routes were the same Atlantic crossings long used by liners and cargo ships, now crowded with escorted merchant vessels.
The Tools of Defence
Several developments eventually shifted the balance:
- Longer-range aircraft flying from Britain, Iceland, Newfoundland and elsewhere, to close the mid-ocean gap where convoys had once been without air cover.
- Escort carriers, smaller aircraft carriers that sailed with convoys.
- Radar and direction-finding, including shipborne marine radar sets, and radio direction-finders that located U-boat transmissions.
- Better escort ships and training, including improved depth charges and weapons, and cooperation between escort groups.
- Codebreaking, where Allied intelligence successes against German naval ciphers, including work at Bletchley Park, at times let convoys be routed away from U-boat concentrations. The Germans also read some Allied signals, so the struggle in intelligence went both ways.
The detail of these developments is complex and historians still debate how far each factor contributed.
The Turning Point
In the spring of 1943 convoy battles were fierce, and Allied shipping losses in March were very high. In April and May, however, U-boat losses rose sharply, and in late May Dönitz withdrew his boats from the North Atlantic. The Germans did not abandon the campaign, and U-boats continued to attack until the end of the war, but they never regained the same chance of cutting the supply line. By then, new building of merchant ships in the United States greatly exceeded the rate of loss. The U-boat was the culmination of decades of work on military submarines, and its limits as a mostly surface-running craft were now being exposed.
The Human Cost
The campaign cost thousands of merchant ships and tens of thousands of lives, including merchant seamen who were not part of the armed forces. Ships such as oil tankers and slow tramp steamers were among the most vulnerable vessels, and their crews faced cold, long watches and sudden attack. German submariners also suffered very heavy casualties, with a large share of the U-boat force lost.
What Made It Decisive
The Atlantic campaign did not produce a spectacular victory. Its importance was that the sea lanes stayed open. That allowed Britain to remain in the war, and allowed the build-up of American forces and supplies that made the invasion of Europe in 1944 possible. A convoy system, careful and unglamorous, proved to be as important as any fleet action.