Changing Methods of Warfare by Land, Air and Sea, 1939-45 » U-Boat Warfare in the Atlantic

Why the Atlantic mattered

This lesson is part of the Paper 2 Section B breadth study on the changing nature of warfare, 1919-2011. Britain is an island and could not feed itself or fight a war on its own resources. It had to import food, oil, raw materials and weapons by sea, much of it from North America. Germany knew this. If its submarines, called U-boats, sank merchant ships faster than they could be replaced, Britain would starve and run out of fuel. Winston Churchill later wrote: "The only thing that ever really frightened me during the war was the U-boat peril."

The fight for these sea lanes lasted from 1939 until 1945 and is called the Battle of the Atlantic. It was a battle of supply, not of famous single clashes.

Key terms:

• Wolf pack: a group of U-boats that hunted together, found a convoy and then attacked it at the same time.
• Escort carrier: a small, cheap aircraft carrier built to sail with convoys and fly aircraft against U-boats.

The U-boat threat: wolf packs

After France fell in June 1940, Germany used French Atlantic ports such as Lorient and Saint-Nazaire as bases. U-boats could now reach the Atlantic much faster and stay at sea longer.

The U-boat commander, Karl Dönitz, did not send his submarines out alone. Instead a few U-boats spread out in a line across a convoy's likely path. The first to spot the convoy radioed its position. The others gathered, then attacked together, usually at night and on the surface. This had two big advantages:

By 1942 the U-boats were sinking ships faster than the Allies could build them. In early 1942 they also hunted along the coast of the USA, where ships at first sailed without convoys. Losses were highest in 1942 and in the early months of 1943. In March 1943 two convoys, HX 229 and SC 122, lost more than 20 ships between them.

The Allied answers

The Allies won the battle not with one weapon but by combining several. Together they made it too dangerous for U-boats to attack.

• Convoys. Merchant ships sailed together with warship escorts from the first months of the war. A convoy was a smaller target in a huge ocean than many ships sailing alone, and the escorts could hunt any U-boat that attacked.
• Sonar and radar. Sonar helped escorts find submerged U-boats. Radar, especially a newer type carried by aircraft and ships, let them find U-boats on the surface at night and in fog. It was the answer to the night attacks.
• Code-breaking. The U-boats talked to their headquarters by radio, using the Enigma machine to scramble their messages. At Bletchley Park British code-breakers read many of these messages. In May 1941 the Royal Navy captured Enigma equipment and code books from the submarine U-110, which helped. Knowing where U-boats were, the Allies could steer convoys around them. Ships also used high-frequency direction finding, which located a U-boat from its radio signal. Germany added an extra rotor to its Atlantic Enigma in February 1942, and Bletchley Park could not read the messages for most of that year. It broke back in during December 1942.
• Long-range aircraft. In the middle of the Atlantic there was a stretch called the "air gap", out of range of aircraft flying from land. U-boats attacked there with little to fear. In 1943 very long range Liberator bombers began to fly from Britain, Iceland and Newfoundland and closed the gap.
• Escort carriers. These small carriers sailed with the convoys, so aircraft were always on hand to attack U-boats, even far from land. Together with extra escort ships they formed groups that hunted U-boats rather than just guarding the convoy.

The Allies were also helped by the industry of the USA, whose shipyards built merchant ships so fast that, by 1943, new ships were being launched faster than the U-boats could sink them.

The turning point, 1943

In May 1943 the Allies sank more than 40 U-boats, so many that the month is called "Black May". Dönitz pulled his U-boats out of the North Atlantic on 24 May 1943. U-boats kept fighting until 1945, but they never again threatened Britain's supplies in the same way. In the whole war about 3,500 Allied merchant ships were sunk, and about 780 U-boats were lost.

Change and continuity

What changed: in 1917 U-boats mostly attacked alone, and the Allied answer was the convoy plus depth charges. In 1939-45 U-boats hunted in wolf packs, and the Allies needed a whole system: radar, aircraft, code-breaking and escort carriers as well as convoys. What stayed the same: Germany again tried to starve Britain by sinking merchant ships, and the convoy was again the key defence.

Exam-style question

Explain TWO causes of the Allied victory over the U-boats in the Atlantic by 1943. [8 marks]

Remember: one cause on its own can score no more than half marks, so write two paragraphs.

Recap

• Britain depended on imports by sea, so the U-boat threat to its supplies was deadly serious.
• Wolf packs attacked convoys together, at night and on the surface.
• Convoys, sonar, radar, code-breaking, long-range aircraft and escort carriers worked together to win.
• The turning point was spring 1943, and "Black May" ended the threat to Britain's supplies.