GPT-6 Astra Cracks a Century-Old WWI German Ship Cipher

A German science blog has posted a WWI German radio message that GPT-6 Astra solved, and the solution is a ship report from 1918. The message describes an English cruiser arriving at Sevastopol and an allied squadron following behind.

The cipher used is ADFGVX, a system where a grid built from a keyword determines how each letter gets replaced. The keyword here is “TRUPPENVERSCHIEBUNG,” rearranged alphabetically before the message is laid out across it. Each letter in the keyword points to a position in the coded text, and working through that math revealed the plaintext.

The Message Decoded

The decoded message reads: “EIN ENGLISCHER KREUZER EINLIEG X SEWASTOPOL X S4STEN X EIN GESCHWADER DER X ALLIIERTEN FOLGT 26STEN X.” In English, that is: “AN ENGLISH CRUISER ARRIVED AT SEVASTOPOL ON THE ?4TH AN ALLIED SQUADRON FOLLOWS ON THE 26TH.”

Astra checked the ship records and found that the cruiser HMS Canterbury did arrive in Sevastopol on November 24, 1918. The allied squadron followed on November 26.

Why It Worked

The cipher had been solved before by codebreaker George Lasry, who decoded hundreds of these messages. But some messages remained unsolved, including one sent on November 27, 1918. Astra’s hypothesis is that “TRUPPENVERSCHIEBUNG” was used as the key starting on December 9, 1918 — later than this message was sent. The reason for that gap is unknown.

The solution matches the ship’s original logs.

How the Cipher Works

ADFGVX works by laying out a message across a grid built from a keyword. Each cell in the grid holds a pair of letters, and the pairs are drawn from six possible values along both axes. The keyword “TRUPPENVERSCHIEBUNG” was rearranged alphabetically before being laid out, with the encrypted message placed beneath it in rows of 19.

The math involves counting columns and symbols. The keyword’s letters point to specific positions in the message, and those positions reveal the plaintext letters.

The Order of Events

1. The cipher was first solved by codebreaker George Lasry, who decoded hundreds of these messages.
2. Some messages remained unsolved, including one sent on November 27, 1918.
3. Astra’s hypothesis is that “TRUPPENVERSCHIEBUNG” was used as the key starting on December 9, 1918 — later than this message was sent.
4. The solution matches the ship’s original logs.

What It Shows

This is a minor but notable result. A language model solved a century-old coded message about ships arriving at Sevastopol.

The fact that the solution checks against real ship records adds weight to it. This particular message had not been decoded before, according to the blogger.

Key Facts Box

• Cipher: ADFGVX
• Keyword: TRUPPENVERSCHIEBUNG (alphabetized)
• Decoded message: cruiser arrived November 24, squadron followed November 26
• Message date: November 27, 1918
• Previously solved by: George Lasry
• Model used: GPT-6 Astra

The Takeaway

Astra’s work shows what happens when a model tackles a problem that humans have left open. The cipher was well understood, but the specific key and date mismatch kept this message unsolved until now.

It is a small victory for machine-assisted history.

Source material: “GPT-6 Astra Solves a WWI German Radio Cipher,” prinzai.com.

AI · codebreaking · cryptography · GPT-6 · history · WWI