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Code Girls

The Untold Story of the American Women Code Breakers of World War II

By Liza Mundy
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Code Girls by Liza Mundy

Code Girls (2017) is about the thousands of American women who worked as code breakers during World War II. Informed by interviews with over 20 surviving women, archived documents, and recently declassified oral histories, author Liza Mundy details the unprecedented lives of female code breakers in Washington, DC and beyond as well as the American intelligence that led to the success of the Allied war efforts.

Key idea 1 of 10

Cryptography bureaus often took on female workers because of the work’s grueling nature.

Cryptography, or code making, is as old as human communication itself. It dates back to some early point in time when a person first wanted to say something that not everyone was supposed to know.

Naturally, making codes is particularly useful in times of war. During the Civil War, for example, the Confederates devised a cryptographic system so complex that it confused even them.

In the early 1920s, however, American code breaking lagged behind that of countries such as France and England. In 1928, the US secretary of state even shut down military intelligence’s modest cipher bureau as it was bad manners to read other people’s mail.

But not everyone dismissed code breaking as immoral. And those who did see its purpose tended to favor women for the job. The assumption was that women were better able to focus intensely over long periods of time than men, who were seen as more intelligent but less patient. The assumption overlooked the fact that good code breaking requires both patience and intelligence.

In order to understand how code breaking works, let’s take a look at the two types of covert message systems: codes and ciphers. Codes are words, letters, or a string of numbers that represent words or phrases. Sometimes codes are used for brevity, in the same way that OMG is used today. But codes can also be used to disguise secret information from an enemy’s prying eyes; those meant to read the code could decipher it using a codebook.

Ciphers, on the other hand, are either a scrambling of letters known as transposition or a substitution of individual units with unique units – for example, substituting r for t. During the Renaissance, ciphers such as the Vigenère square were created by lining up various alphabets into a table that could be referenced. But with the development of radio and the telegraph, governments needed more security. So they created cipher machines as well as developing complicated ciphers using mathematical equations.

Tackling messages intercepted by cable, airmail, or teletype – that is, cryptanalysis, or code breaking – involved many tactics. In some cases, codes were cracked by stealing codebooks from the enemy. But more often, cryptanalysts cracked codes by studying the frequency and placement of specific words, using mathematical equations, and deducing meaning through educated guesses.

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