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Document of the Week: Secret Codes in the Second World War

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Authored by Dr Charlie Hall
Published on 3rd March, 2025 2 min read

Document of the Week: Secret Codes in the Second World War

An aged piece of paper with several illustrations drawn on it in thick pen. It is a letter from a Spanish convent in Lisbon to one in Britain. It uses simple hand-drawn images to convey words, or part of words, in Spanish, often merely because they sound alike. For example, a picture of a wound (herida in Spanish), positioned between K and S, becomes queridas, or dear. Some of the illustrations include a pair of wings, a mother holding two children, a snake, two oars, an envelope, and music notes.

Our latest “Document of the Week” was chosen by our Senior Curator, Dr Charlie Hall. It forms part of a file assembled towards the end of the Second World War, recording the different codes and cyphers which British censors had encountered during their close scrutiny of postal and telegraphic communications throughout the conflict. Cracking these codes allowed censors, and the British security and intelligence establishment more widely, to understand the information which was being transmitted in and out of British territory.

This file contains many fascinating examples of the ways in which correspondents of all kinds sought to keep their messages concealed from the censors. This example, a letter from a Spanish convent in Lisbon to one in Britain, is especially striking. It uses simple hand-drawn images to convey words, or part of words, in Spanish, often merely because they sound alike. For example, a picture of a wound (herida in Spanish), positioned between K and S, becomes queridas, or dear.

The content of this particular communication is pretty innocuous but the document offers an intriguing insight into the ways in which hostile or subversive elements could conceal secret or sensitive information in their messages, and the challenges which censors faced in deciphering them.

Where to find this document

This item comes from our primary source collection, Censorship: Policy and Practice during the Second World War. Comprising, over 17,000 images drawn from the Ministry of Defence files at The National Archives (UK), this collection explores a vital aspect of Britain’s wartime security.

Postal and telegraph censorship was a crucial tool utilised by the British government during the war to keep sensitive information from falling into enemy hands, to root out spies and traitors, and to monitor public opinion and morale. Visit the collection page to learn more.


Authored by Dr Charlie Hall

Dr Charlie Hall

I am a Senior Curator at BOA and a Senior Lecturer in Modern European History at the University of Kent. My research interests lie in conflict, technology and society in the twentieth century, with a particular emphasis on Britain, Europe and North America.


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