During the Second World War, signals intelligence (SIGINT) was vital to gather information on the enemy. The British Government Code and Cipher School (GC&CS) at Bletchley Park was responsible for cryptanalysis, the breaking of diplomatic communications and enemy military codes and ciphers, at both tactical and strategic level. The intelligence, derived from high-level encrypted communications, was codenamed ULTRA. The main focus was on the German Enigma and Lorenz cipher machines, as well as various other German and Italian radio communications. This information played an important and often decisive role during World War II.

One of these was Colossus, the world's first operational programmable digital electronic computer, developed by mathematician Max Newman and built by Tommy Flowers from the Post Office Research Station. The Colossus assisted in breaking the Lorenz SZ40/42 teleprinter traffic. More about the Colossus on our website in English or Nederlands.

In 1945, about 9,000 people worked at Bletchley Park and various outposts. Although primarily known for its brilliant codebreakers, including Alan Turing, John Tiltman, Gordon Welchman, and Dilwyn Knox, many outstanding female codebreakers also worked at Bletchley Park. Among them were Joan Clarke, Mavis Batey, Margaret Rock, Ann Katharine Mitchell, and many others.

The Bletchley Park Podcast shares fascinating stories about the codebreakers, both male and female, the vast workforce that supported them, and the machines they developed. The podcast also explores the breaking of Axis military and diplomatic communications, and how its intelligence influenced the outcome of famous battles on land, at sea, and in the air.

Visit the Bletchley Park Podcast or explore all 292 episodes and extras at Apple Podcasts. More about visiting the museum on the Bletchley Park Website. Highly recommended!

Brian Neal successfully completed our Enigma Challenge in 2012. Since then, he was hooked on crypto machines and started that same year his own Py-Enigma project which found its way to GitHub. Last December, Brian created the website ww2crypto.online to make his browser-based Enigma simulation available to everyone. He also developed a simulation of the U.S. M-209, is working on the Japanese PURPLE machine, and plans to develop more crypto machines to run in your browser.

More information on Brian Neal's project:

• ww2crypto.online Enigma
• Py Enigma Project Page
• Python Py-Enigma’s documentation
• Enigma simulator on GitHub

Keep an eye on ww2crypto.online as several simulations will be added in the coming months.

TSEC/KL-7

We have just published version 5.3 of the history of the TSEC/KL-7 cipher machine. Our first encounter with the KL-7 was in 2005 aboard the battleship HMS Belfast, where it was displayed behind glass. It then took six more years of research to create an accurate simulation of this Cold War cryptologic marvel. None of this would have been possible without the help of Paul and Marc from the Crypto Museum, the late George Mace, and Bill Neill’s FOIA contributions. Their assistance was invaluable in unraveling the technology behind the KL-7.

The William Friedman Collection was a treasure trove that detailed the design choices and development of the KL-7. Historical records from the U.S. Army Security Agency contained production details, planning and procurement, and reports on its use in Vietnam. The first version of the KL-7 history was published in 2022 and included references to all relevant ASA, AFSA, NSA, CIA, and NATO files. In the following years, many more documents and bits of information surfaced, including FBI documents and counterintelligence records about the KL-7's compromise by John Walker and Joseph Helmich. The research began in 2005, and although all technical documents were declassified in 2009, the research ultimately took nearly two decades as additional records were released gradually.

The newest version offers the most detailed history of the TSEC/KL-7 ever published, but research continues. Its use of electronics, worldwide deployment in both war and peace, and involvement in espionage cases make the KL-7 a true Cold War icon, deserving its place in cryptologic history.

History of the TSEC/KL-7 ADONIS and POLLUX version 6.1 (Updated 14 May 2026)

This is the definitive history of the KL-7 unless we discover additional information. Former operators and technicians can help us preserve cryptologic history by sharing personal experiences with the now-declassified KL-7. We already documented stories from a U.S. crypto tech at the Air Base Saigon, a U.K. tech at JHQ Rheindahlen, and a British merchant radio operator during the Falklands War. However, more stories about the KL-7 are essential to preserve its history.

More about the TSEC/KL-7 in English or Nederlands with all technical details and full history.