What this lesson teaches
I can weigh up the reasons the Allies won and World War II ended in Europe and the Pacific.
Syllabus K330, War in Europe and the Asia-Pacific, Learning Outcomes. Assess the reasons for the end of World War II.
Make a guess
German U-boats sank huge numbers of cargo ships heading for Britain. What do you think finally beat them by May 1943?
- Breaking the Enigma code, which ended the threat on its own.
- Germany ran out of submarines early in the war.
- Convoys, codebreaking, escort ships and long-range aircraft together.
Show the answer
Convoys, codebreaking, escort ships and long-range aircraft together.
Reading Enigma showed where wolf packs waited, while escorts and aircraft hunted them. No single tool won alone.
Codebreaking, escorts and aircraft beat the U-boats by May 1943, so American troops and supplies could cross to Britain and Europe.
American factories helped only if their goods crossed the Atlantic Ocean. Britain needed imported food, fuel and weapons to survive. German submarines, called U-boats, hunted the cargo ships in groups known as wolf packs. The struggle to keep the sea routes open is called the Battle of the Atlantic. It lasted the whole war in Europe, from 1939 to 1945.
The Allies sailed cargo ships together in convoys, guarded by warships. Codebreakers helped too. German U-boats got their orders by radio, scrambled by a machine called Enigma. At Bletchley Park in Britain, Alan Turing's team broke the naval Enigma code in the second half of 1941. Reading the messages showed where the wolf packs were waiting, so convoys could be steered around them. This secret intelligence was called Ultra.
In February 1942 the German navy added an extra wheel, or rotor, to its Enigma machines. The codebreakers were shut out, and Allied shipping losses in late 1942 were three times those of late 1941. By the end of 1942 the new code was broken again.
In spring 1943 the Allies combined codebreaking with radar, small aircraft carriers that sailed with the convoys, and long-range patrol planes. So many U-boats were sunk in May 1943 that on 24 May the German admiral Karl Doenitz pulled them out of the North Atlantic. American shipyards were now building cargo ships faster than U-boats could sink them. The sea route stayed open, so the troops and supplies for D-Day could be gathered in Britain.
- Battle of the Atlantic
- The 1939 to 1945 struggle between U-boats and Allied convoys for the sea routes to Britain.
- Enigma and Ultra
- Enigma scrambled German orders; Bletchley Park broke it, and the intelligence was called Ultra.
- May 1943
- Heavy U-boat losses; on 24 May Doenitz withdrew them from the North Atlantic.
Real examples to use
Losing the code, 1942
After the German navy added a fourth Enigma rotor in February 1942, Allied convoy losses in late 1942 were three times those of late 1941.
Black May, 1943
Codebreaking, radar, escort carriers and long-range aircraft sank so many U-boats that Doenitz recalled them from the North Atlantic on 24 May 1943.
Ships faster than sinkings
The USA built 2,710 Liberty cargo ships from 1941 to 1945, so by 1943 new ships outnumbered those the U-boats sank.
Worked example: How a broken code saved a convoy
A convoy is crossing the Atlantic while a wolf pack waits on its route.
- Codebreakers read the Enigma orders that tell the U-boats where to wait.
- The convoy is steered around them, so its ships and cargo arrive.
- More supplies reach Britain, which later lets the Allies build up forces for D-Day.
Watch out for this
Breaking Enigma won the Battle of the Atlantic on its own.
Codebreaking worked together with convoys, escorts, radar, aircraft and US shipbuilding. When the code was lost in 1942, losses rose, but the other tools still mattered when it was broken again.
Check your understanding
How did breaking the naval Enigma code help the Allies?
- It let the Allies win the Battle of the Atlantic within weeks in 1941.
- It showed where U-boats were waiting, so convoys could be steered away from them.
- It let the Allies find U-boats by tracking the direction of their radio signals.
Show the answer
It showed where U-boats were waiting, so convoys could be steered away from them.
Yes. Ultra intelligence let the Allies avoid wolf packs, so more supplies reached Britain.