Nobody Could Decode This 108-Year-Old German Military Cipher. AI Just Did.
Nobody Could Decode This 108-Year-Old German Military Cipher. AI Just Did.
Elizabeth RayneThu, October 1, 2026 at 6:00 PM UTC
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AI Cracked a 108-Year-Old WWI CipherBjoern Wylezich - Getty Images
Here’s what you’ll learn when you read this story:
During WWI, German officers sent a coded warning to their High Command about an English cruiser and Allied forces converging on Sevastopol.
The message went unread for 108 years, until OpenAI's new GPT-6 Astra decrypted it.
The model may go on to unlock other historical ciphers.
In 1918, near the end of the First World War, German military officials transmitted a cryptic message about an English cruiser on its way to Sevastopol. They also reported that an Allied squadron would soon arrive and be waiting to strike near the Crimean Peninsula. Now, 108 years later, with the help of software developer Prinz, the infamously unsolved cipher has finally been decrypted by AI.
OpenAI has claimed GPT-6 Astra is an “alien mind” because of how sophisticated this clump of digital neurons is—the LLM boasts uncanny intelligence that makes it more humanlike. It can solve complex tasks and even beat the video game Portal in only 24 hours by mapping 3D spaces in the game and devising ways to solve its puzzles. Astra was given the keyword the Germans had used—“TRUPPENVERSCHIEBUNG,” or troop redeployment—a reminder that cipher keys were chosen for convenience, not relevance, since the message it unlocked concerned a warship. And sure enough, the plaintext of the message matches the historical record, since the H.M.S. Canterbury’s original log states that it was heading to Sevastopol from Constantinople.
In the ADFGVX method of encoding, which was used by the Germans during World War I, the letters “ADFGVX” are arranged horizontally and vertically next to six rows of six letters each that start with the keyword (which needs to be rearranged so all of its letters are in alphabetical order) and segue into the alphabet and every number from 0 to 9. It reads like a graph where the value lies at certain points on the X and Y axis. Encrypting a letter is shockingly easy. It depends on which points on the chart correspond to the location of that letter, so if it happens to be four characters down in row F and three characters up in column D, then the code for that letter is AD. This is why “AV” corresponds to “E”, the first letter of the first word that was transmitted, and so on. The resulting message will look horribly garbled as intended:
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The ADFGVX Cipher employed by the German military in World War IEncyclopaedia Britannica - Getty Images
What the Germans were actually trying to communicate to their High Command with this cipher (which was probably intended for Naval Command or an officer of high rank such as an admiral) was “EIN ENGLISCHER KREUZER EINLIEG X SEWASTOPOL X S4STEN X EIN GESCHWADER DER X ALLIIERTEN FOLGT 26STEN X,” which translates to “AN ENGLISH CRUISER ARRIVED AT SEVASTOPOL ON THE ?4TH AN ALLIED SQUADRON FOLLOWS ON THE 26TH.”
Astra also figured out that although the key was first put into use on December 9, 1918, the message was actually transmitted on November 27, 1918. The reason why is unknown. When the AI checked itself against the log, it discovered that the H.M.S. Canterbury arrived in Sevastopol even earlier, on November 24, 1918. An Allied squadron then arrived on November 26, a day before Germany sent the message. What the question mark right before “4th” means is unknown. It might have been a typo, which apparently still happened even when conducting top secret military operations.
“I am not aware of this particular message having ever been decoded before,” a spokesperson for Prinz recently said in a statement on their website, “so sharing it here as a minor (but I think really cool) result and illustration of the capabilities of this model.”
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