Colossus: Never-Before-Seen Photos Show The Computer That Helped Win WW2

Along with kicking Nazi ass, Colossus was an important precursor to the device you're reading this on.


Tom Hale


Tom Hale

Senior Journalist

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

Edited by Francesca Benson

Francesca Benson

Copy Editor and Staff Writer

Francesca Benson is a Copy Editor and Staff Writer with a MSci in Biochemistry from the University of Birmingham.

A black and white photograph of Colossus, the UK's secret code-breaking computer credited with helping the Allies win World War Two.

Occupying the size of a room, Colossus didn't look anything like a modern computer.

Image credit: Crown Copyright – reproduced by kind permissions of Director GCHQ

This is the computer that helped secure the Allied victory in the Second World War and sent the Third Reich to the trash can of history.

GCHQ, the UK’s intelligence agency, has unveiled never-before-seen images of the code-cracking computers that played a crucial role in the Second World War. They’ve been released to mark the 80th anniversary of the machine arriving at Bletchley Park, where it began to work its wonders. 


The Colossus computer was the world's first programmable, electronic, digital computer. It was created by the British during World War Two to decipher messages between Adolf Hitler, his entourage of leading Nazis, and senior German generals. 

The computer’s sole job was to decipher German radio messages that had been encrypted by a Lorenz cipher. Using around 2,500 valves, Colossus would recognize patterns and perform statistical analysis that worked out the settings of the cipher machine's 12 wheels, thereby allowing them to read the coded message.

Black and white photograph of the Colossus computer at Bletchy Park taken in the 1960s.
Another shot of Colossus.
Image credit: Crown Copyright – reproduced by kind permissions of Director GCHQ

One of its most significant achievements was revealing that Hitler had been successfully dubbed into thinking that the Allies would be launching their D-Day invasion of mainland Europe from Pas De Calais, not Normandy. This sneaky act of deception helped to ensure the Normandy Landings were a success for the Allies (albeit a very costly one).

“Colossus was perhaps the most important of the wartime code breaking machines because it enabled the Allies to read strategic messages passing between the main German headquarters across Europe,” Andrew Herbert OBE FREng, Chairman of Trustees at The National Museum of Computing, said in a statement.


Along with its role in World War Two, the pioneering device paved the way for the development of modern electronic digital computers. Experts who worked on the war-winning computer went on to develop “the Manchester Baby” in 1948, which was the world’s first electronic stored-program computer.

Colossus was developed by a team of engineers led by British General Post Office engineer Tommy Flowers. The work of Alan Turing helped inspire parts of its design, although this computer engineering legend did not work directly with the Colossus project. 

Black and white photograph of the code-breaking computer Colossus that helped Allieis with WW2
We owe you one, Colossus.
Image credit: Crown Copyright – reproduced by kind permissions of Director GCHQ

The gigantic device was stationed at Bletchley Park, a quiet country house in Milton Keynes that became the powerhouse of the Allied code-breaking effort during World War Two. 

Despite this huge historical importance, Colossus remained a highly classified state secret for decades. Its existence was revealed in 1975, but it was not until the early 2000s that substantial information about the project was released to the public.


“I worked as an engineer on Colossus for a year during the 1960s. I had just signed the Official Secrets Act and knew nothing about GCHQ but was offered ‘interesting work’ which I believed would be dealing with telegrams for a government department,” explained Bill Marshall, a former GCHQ engineer.

“I was told very little about the machine I was working on – what the machine was actually doing was not for me to know. My job was to repair it as necessary, using just a few circuit diagrams and no detailed user handbook. It wasn’t until much later that I found out that the several of the systems and detailed design information were supposedly destroyed at the end of WWII,” Marshall added.

Sadly, the original machine is no more. Following the end of the war, Cold War paranoia quickly sunk in. Eight out of the ten Colossus machines at Bletchley Park were promptly dismantled to ensure the technology did not fall into the hands of the Soviet Union. The remaining two, which were kept by British Intelligence, were later destroyed in the 1960s.

There is, however, a fully working reconstruction of a Colossus computer that you can see at the National Museum of Computing at Bletchley Park.


  • tag
  • history,

  • computers,

  • alan turing,

  • code-breaking,

  • computer science,

  • ww2,

  • Adolf Hitler