U-boat Calling...

German U-boats (submarines) were a major threat to Allied ships during the first four years of the war.

U-boats patrolled the Atlantic and other oceans in 'wolfpacks', hunting for convoys of British and American ships.

A U-boat commander communicated with his
headquarters by wireless. This is the way a message was sent:

• The rotors and plugs on the Enigma machine were changed to that day's setting given in a codebook.
• The message was typed using the bottom keyboard.
• As each letter was typed, a different 'code' letter lit up on the top alphabet.
• These code letters were written down to make the secret message.
• The message was then sent by wireless using Morse code.

How were the messages intercepted?

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Enigma home

Codes in wartime

Making codes

Codes and ciphers

Breaking codes

Codes in history

Morse code

The Enigma Machine

The U-boat threat

Inside a 'Y' Station

Bletchley Park

Bombes

Code books

Colossus

ULTRA

The code-breakers' legacy