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.

U is for U-Boats

I wrote about Enigma for my E post, but that post got long before I got to give any examples about exactly how the Allies were able to utilize decoded Enigma messages to improve their chances at winning the war.

A big factor was that the Allies could use Enigma messages to track the movement of German U-boat submarines.

The Battle of the Atlantic was a war of lives and of commerce. England needed food. The Allies needed troops and war materiel to press their campaigns in Italy and North Africa. American shipyards were churning out Liberty ships—low-cost cargo ships that were being mass-produced in unheard-of numbers—but the U-boats in 1942 were able to sink ships faster than America could make them. (p. 134, Code Girls by Liza Mundy)

Kriegsmarine U-boat by Augusto Ferrer-Dalmau CC BY-SA 3.0, Link

When the Allies were able to break Enigma messages, the convoys could be re-routed to safer paths. But for a long dark time during 1942, the Allies were locked out of the German naval Enigma.

The [Enigma code-breaking] effort at no time was easy, but it became excruciatingly difficult after February 1942, when the German subs started using the four-rotor naval Enigma, and Allied efforts against it proved mostly futile…. [T]he impenetrability of the four-rotor Enigma kept them at a major disadvantage until, in late October 1942, four British destroyers patrolling the easter Mediterranean targeted and attacked a U-boat, the U-559. The submarine, which had surfaced, began to sink and a group of British sailors tore off their clothes, dove into the water and swam over to it, to retrieve papers and equipment. Two of the sailors, an officer and a seaman were coming up a ladder when a rush of incoming water overcame them, and they went down with the sub. The others were able to scramble into a whaler. The men had retrieved two books, one of them a weather cipher book giving current key settings, which found its way to Bletchley Park and helped the code breakers get into the four-rotor Enigma cipher. (p. 268)

Spoiler Alert: I’m about to talk about how this incident shows up in The Rose Code by Kate Quinn. If you haven’t read that novel and don’t want any part of it spoiled before you do, then stop reading this post. Leave a comment and let me know when you plan to read The Rose Code so that I can cheer you on.

This incident is covered in The Rose Code by Kate Quinn, adding depth and drama between one of the main characters, Beth Finch, and her love interest, Harry Zarb.

Here is how Kate Quinn describes the celebration at Bletchley Park on the day that they cracked the four-rotor Enigma cipher:

Beth waved to the hockey players and picked her way across the icy lake path, pausing midway as she saw a mass of Hut 8 cryptanalysts spilling across the lawn, cheering at the top of their lungs. Brilliant Joan Clarke, whom Dilly wished he’d poached for his section; Rolf Noskwith drinking directly out of a wine bottle—and Harry, veering away from the pack and picking Beth up, swinging her over the frosty grass.

“We did it, we bloody did it! A pinch off U-559—we’re back in. We’re back in the bloody U-boat traffic!”

“Harry!” She kissed him jubilantly, every worry that had been consuming her falling away. “I knew you’d get in.”

People were spilling out of huts and blocks, letting out cheers as the news spread. The U-boat blackout had gone on too long not to be common knowledge at BP, even if no one outside Hut 8 knew details. (pp. 396-7)

Since British sailors were the initial heroes and British codebreakers performed the cryptography, I’ll share this post on Friday with the British Isles Friday folks.