The A to Z Challenge asks bloggers to post 26 posts, one for each letter of the English alphabet, in April. Most of us choose to make these posts on a particular theme. My theme for 2022 is Codebreaking in World War II, which fits with the topic of the novel that I’m writing. Visit every day (except Sunday) in April for a new post on my topic.

K is for Alfred Dillwyn “Dilly” Knox

Dillwyn “Dilly” Knox was a British codebreaker. Fans of The Rose Code, about codebreaking at Bletchley Park, will recognize him as one of the most vividly painted historical characters in that novel. But he was around long before then and had a hand in two famous incidents.

First, Knox was part of the team that decrypted the Zimmermann Telegram. In January 1917, the German foreign minister, Arthur Zimmermann, invited Mexico to invade the United States as a German ally in return for Texas, Arizona, and New Mexico. The British turned this information over to the US and it was a primary reason that the US entered World War I.

The Zimmermann Telegram also made it clear to the US government that they needed cryptographers, which is when the Friedmans were recruited to bring the US up to speed.

Twenty years later, Knox was on the team that met with Polish cryptographers on the eve of World War II to learn about their progress in breaking Enigma, which gave Bletchley Park a running start on their efforts.

During World War II, Knox led the team working in “the Cottage” next to the Bletchley Park mansion. Alan Turing gets all the glory for inventing a proto-computer to solve Enigma. But there were many varieties of Enigma and lots of the messages continued to be deciphered by hand, throughout the war.

Knox’s unit used a technique that he invented called rodding, a way of finding common phrases (called cribs) in an enciphered message. His team decrypted messages from the Italian Naval Enigma that provided intelligence vital to the victory at the Battle of Cape Matapan. They also worked on the Abwehr Enigma (the variant that was used by German military-intelligence), uncovering important details that helped with planning the D-Day invasion.

Since the books I have at home are about American code-breaking, my information on Dilly Knox is from the Wikipedia article. I’m intrigued by two books: Dilly: The Man Who Broke Enigma by Mavis Batey and The Knox Brothers, written by Penelope Fitzgerald, niece of Dillwyn Knox. Fitzgerald is more famous for her novels, including The Blue Flower and The Bookshop.

I’ll share this post on Friday in the British Isles Friday link party.