A reconstruction of a major piece of cybernetic history and the precursor to Colossus, the world's first programmable electronic digital computer, has made its public debut at the National Museum of Computing at Bletchley Park, Buckinghamshire, UK. The working replica of the Heath Robinson code-breaking machine that was used to read secret top-level Nazi messages during the Second World War was unveiled by wartime Wren Irene Dixon.

Not as well-known as in his heyday, W. Heath Robinson was an illustrator and cartoonist who was famous for his drawings of insanely complicated devices made out of everyday objects that were supposed to carry out the simplest of tasks, like making pancakes or putting holes in Swiss cheese. Therefore, it wasn't surprising that when the famous code-breaking team at Bletchley park built an incredibly intricate electromechanical machine to help crack the German Lorenz code, the Wrens (Women's Royal Navy Service) personnel who ran it gave it the nickname "Heath Robinson."

The Heath Robinson was commissioned by the Newmanry section of Bletchley Park under Max Newman and largely built by the Telecommunications Research Establishment at Malvern to crack the Lorenz code. It went online in June 1943 and enjoyed a successful, through problematic career.

Much more advanced than the famous Enigma code, Lorenz was generated by the SZ40/42 teletypewriter in-line cipher machine (code named "Tunny" by the British) built by C. Lorenz AG in Berlin. The cipher machine produced what is called a Vernam cipher using 12 rotor wheels linked in an eye-wateringly intricate manner based on the Boolean XOR function. The meant that a message encrypted by the Lorenz machine was incredibly difficult to decrypt because the wheel settings used to write it were indispensable to reading the message.

Put simply, Heath Robinson used a statistical method to analyze the coded messages called the Tutte 1+2 technique to crack the Lorenz cipher. In this, the machine ran two tapes –one had the encrypted message and the other a component of the possible decoding key. The key tape was one character longer, so the key could be tested against each character of the ciphertext.

To do this, the two perforated tapes had to be kept in rigid and precise synchronization. This meant running the tapes through an elaborate "bedstead" tape feed as they were scanned and read by banks of photoelectric cells. It was a system that worked, but it was difficult to run, required the tapes to be changed many times to handle the Lorenz wheel settings, was hard to maintain, and couldn't scale.

To overcome these setbacks, Tommy Flowers of the General Post Office (GPO) laboratories in Dollis Hill, London decided to abandon the Heath Robinson and start over to develop the breakthrough computer that would be known as Colossus that used radio valves instead of tapes to handle the code-breaking data in digital form.

According to the museum, Heath Robinson was not retired, but continued work after Colossus went operational in February 1944. Two "Super Robinsons" were built by the end of the war with two more under development. One of these continued to be used by the Ministry of Defence into the 1950s and a combined version of Robinson and Colossus, called Colorob, went online in 1955.

Unfortunately, budgets and security considerations meant that the Heath Robinsons, as was the case with Colossus and many other early British computers, were eventually dismantled and broken up. The new version on display was reconstructed from the original plans.

Unfortunately, the Heath Robinson's spiritual father died long before its existence was made public, but W. Heath Robinson's nephew, art historian Peter Higginson was present at the unveiling, and museum volunteer Helen Jarvis re-enacted the Wren's task of reading the results from a dashboard display.

"It is such a delight to see this incredible reconstruction of the Heath Robinson machine," says former Colossus Wren Irene Dixon. "It is a fantastic achievement and good to meet Peter too whose great uncle made us laugh with his comical cartoons.

"Seeing all this brings back many memories of my arrival at Bletchley Park in late 1943 to work on the new Colossus machine. I was able to see Wrens working on the original Heath Robinson. It produced good results, but the tapes broke so often that it was a major job to repair them. That was a tedious full-time glue job for somebody. In later years I was able to reassure a former Wren that she had been doing valuable war work."

The Heath Robinson is on display at the National Museum of Computing along with an exhibition of original Heath Robinson wartime illustrations on loan until June 30 from the Heath Robinson Museum in Pinner, London.

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