Engineer, Tommy Flowers, built the world’s first electronic, digital computer in 1943. It was called the Colossus and it took him from February until December – eleven months. It was used by British codebreakers to help read German messages during World War II that were encrypted with the Lorenz SZ40/42 machine. The codebreakers used thermionic valves (vacuum tubes) to perform the calculations.

The Colossus was used to find possible key combinations for the Lorenz machines – rather than decrypting an intercepted message in its entirety. The first Colossus, Mark 1, was followed by nine Mark 2 machines, the first being commissioned in June 1944, and the original Mark 1 machine was converted into a Mark 2. An eleventh Colossus was essentially finished at the end of the war.

Because of the effort to maintain the secrecy of the project right up to 1972 most of the Colossus hardware and blueprints were destroyed. This deprived some of the Colossus creators of credit for their pioneering advancements in electronic digital computing during their lifetimes. Thus, Colossus could not be included in the history of computing hardware for many years. EDVAC was the early design that had the most influence on subsequent computer architecture.

In 1993, Tony Sale started the Colossus Rebuild Project and in 1994 a team led by Sale began to recreate the massive machine at The National Museum of Computing at Bletchley Park in the UK. In spite of the blueprints and hardware being destroyed, a surprising amount of material survived, mainly in engineers’ notebooks, but a considerable amount of it in the U.S. The optical tape reader might have posed the biggest problem, but Dr. Arnold Lynch, its original designer, was able to redesign it to his own original specification.

On June 6th, 1996, the recreated Colossus was first switched on and by 2007 a fully functional replica of the Colossus Mark 2 was completed. To celebrate the project completion a Cipher Challenge was instigated and pitted the rebuilt Colossus against radio amateurs worldwide in being first to receive and decode three messages enciphered using the Lorenz SZ42 and transmitted from radio station DL0HNF in the Heinz Nixdorf MuseumsForum computer museum. Radio amateur Joachim Schüth, who had developed his own signal processing and code-breaking code using Ada, easily won the challenge because the Colossus team were hampered by their wish to use World War II radio equipment. This delayed them by a day because of poor reception conditions. However, Schüth was still impressed with Colossus saying, “”My laptop digested ciphertext at a speed of 1.2 million characters per second—240 times faster than Colossus. If you scale the CPU frequency by that factor, you get an equivalent clock of 5.8 MHz for Colossus. That is a remarkable speed for a computer built in 1944.”

Tony Sale was equally pleased. “On the strength of today’s performance Colossus is as good as it was six decades ago”, he commented. “We are delighted to have produced a fitting tribute to the people who worked at Bletchley Park and whose brainpower devised these fantastic machines which broke these ciphers and shortened the war by many months.”

Andy Taylor, a systems analyst and retro computer enthusiast in the UK, visited the museum in March 2010 and took these photos. For more information on Andy’s collection of vintage computers, check out his website Retro Computers (www.retrocomputers.eu) or his Flickr photostream (www.flickr.com/photos/andysretrocomputers).