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The History of Colossus Computer

Hi there! Today I‘m excited to dive into the fascinating history behind one of the most important early computers – the revolutionary Colossus machine built by British codebreakers during World War II to crack the Nazi‘s toughest encryption systems. This incredible feat of engineering gave the Allies a crucial edge in the war by unlocking Germany‘s secrets.

Let me walk you through the key events and innovations that made Colossus such a game-changer in the evolution of computers…

The Enigma Code – Germany‘s Encryption Advantage

To understand Colossus, we first need to talk about Enigma – the encryption machine used by Germany to encode most of their communications. Enigma looked like an old-fashioned typewriter and used a complex system of rotating wheels and plugs to scramble messages into indecipherable code.

The Nazis believed Enigma was unbreakable, but Polish mathematicians had worked out how to crack the code before the war. They shared what they knew with Britain and France, giving the Allies a head start on decoding Enigma.

At Bletchley Park, genius mathematicians like Alan Turing built electromechanical machines called "Bombes" to rapidly test Enigma settings and decrypt messages. The intelligence gained from Enigma was called Ultra, and Churchill later said it shortened the war by two to four years.

But in 1941, disaster struck for the codebreakers when Germany upgraded to an even more secure cipher system for their high-level communications.

The Unbreakable Lorenz Cipher

This new encryption machine was called Lorenz – and it used a far more complex cipher generation system called Vernam, making it incredibly difficult to crack. The British code-named these new Lorenz-encrypted messages "Tunny".

John Tiltman, one of Bletchley Park‘s top codebreakers, was tasked with trying to break Tunny. Through painstaking analysis, he figured out it was using the Vernam system – which was theoretically unbreakable.

But Tiltman caught a lucky break in August 1941 when two careless German operators sent the same message twice with identical machine settings. This allowed him and colleague Bill Tutte to fully decrypt both matching messages for the first time.

This breakthrough revealed the logic of the Lorenz system. However, manually working out the message settings still took several weeks – too slow to take advantage of the intelligence when it was finally unlocked.

To speed up the process, mathematician Max Newman proposed building an automated computing machine to help test the Tunny settings.

The Birth of Colossus

Newman specified requirements for a high-speed codebreaking computer. The engineers at Dollis Hill built a machine called Heath Robinson using electromechanical relays and valves. It worked but was unreliable and complex.

Newman realized they needed electronic circuits to achieve more speed. He partnered with Tommy Flowers, a brilliant Post Office engineer who was an early pioneer of electronics.

Flowers designed Colossus to incorporate Newman‘s ideas and run five times faster than Heath Robinson. His key breakthrough was using electronic shift registers and ring counters to emulate the Lorenz machine‘s logic, eliminating fragile paper tapes.

Constructed in 1943, the Colossus Mark 1 contained 1500 vacuum tubes and hundreds of logic gates. It could read 5000 characters per second – a blistering speed for that era!

Colossus was highly parallel – five processing units evaluated different parts of the message simultaneously. This enabled incredibly fast pattern matching to deduct the message settings.

The first live test of Colossus in January 1944 blew the codebreakers away. It decrypted messages in hours instead of weeks, proving it could crack Tunny fast enough to produce actionable intelligence.

Colossus Goes Operational

After D-Day, intercepted Lorenz traffic surged as German lines got bombed. An improved Colossus Mark 2 was quickly built and more units were deployed to handle the load.

By 1945, there were 10 operational Colossus computers at Bletchley Park. Their Tunny decrypts provided invaluable intelligence about German plans and vulnerabilities, giving the Allies a crucial edge strategically.

Some key insights from Colossus:

  • Hitler was fooled about the real D-Day invasion target, keeping Panzer tanks away from Normandy
  • V2 rocket production sites were pinpointed, enabling targeted bombing
  • Intelligence showed Germany‘s weak defenses during the Battle of the Bulge in 1944, giving Eisenhower confidence to counter-attack

By the end of the war, over 63 million characters of Tunny messages had been decrypted with Colossus‘s help. The intelligence advantage was enormous. Eisenhower credited these decrypts as being decisive in winning the war.

Colossus: Technical Marvel of Its Time

So what made Colossus such a technological marvel? Let‘s look under the hood…

Colossus was built with state-of-the-art vacuum tubes for speed and reliability. Clever engineering by Flowers enabled it to run stably at 5 MHz clock speeds with a 1.2 microsecond logic gate delay – very fast for that era.

The highly parallel architecture allowed optimized analysis of the 5-channel paper tape input in parallel. Independent processing units simultaneously tested different hypotheses to deduce the message settings.

With 1500 vacuum tubes and a programmer-adjustable logic function, Colossus was the first reprogrammable electronic digital computer. Temporary storage used ultra-fast shift registers to match the processing pace.

Programming was done through switch and plugboard settings that altered the logic. Output was printed on a speedy electric typewriter.

While not a general purpose computer, Colossus pioneered revolutionary hardware and architectures that became integral to later computing advancements.

The Legacy of Colossus

After the war ended, Colossus was dismantled and kept secret to protect British computing knowledge leadership. Details only emerged decades later when engineers were finally able to share their story.

A fully functional Colossus replica was built in 2007 at The National Museum of Computing and proved it could still outpace a modern laptop in a codebreaking speed test when adjusted for clock speed.

Colossus demonstrated the practical potential of electronic digital computing five years before ENIAC and other early computers. Its pioneered technologies and codebreaking capabilities make Colossus one of the most important and influential computers in history.

Though short-lived, Colossus helped the Allies win World War II and shaped the evolution of modern computing as we know it. Its successful decryption of the ‘unbreakable‘ Lorenz cipher remains one of the greatest triumphs in cryptanalysis.

I hope you enjoyed learning about the groundbreaking engineering and crucial war role of the Colossus computer! Let me know if you have any other questions about this revolutionary machine.


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