Yesterday the National Museum of Computing at Bletchley Park celebrated something very special – the 70th anniversary of the first time the world’s first computer was used to attack a message sent by the German high command.
Lorenz isn’t as famous as the weaker Enigma cipher but Bletchley Park’s break into it in 1941 gave the Allies a much bigger and more detailed picture of the Nazis’ overall strategy. Enigma was used to encipher secret messages regarding day-to-day operations whereas Lorenz, which is what Hitler used to encipher his personal messages, was used to communicate orders from the very top.
Enigma had a vast number of different possible machine set-ups on any given day – about 158 million million million. But Lorenz was a million times stronger than THAT. So to read these messages faster Bletchley Park had to come up with the world’s very first semi-programmable computer – Colossus, designed by General Post Office engineer Tommy Flowers.
For years, Bletchley Park deciphered Lorenz either by hand or with the help of Heath Robinson – the forerunner to Colossus.
I was invited by the National Museum of Computing at H Block, where I volunteer as a guide, to take part in a reenactment of the work carried out to decipher a Lorenz message. First, the Auxiliary Territorial Service girls at Knockholt in Kent intercepted the Lorenz messages, which had been translated by the Germans into international teleprinter code. The ATS punched up the messages onto long bits of perforated tape.
The tape, which could be thousands of characters long, was sent to Bletchley Park where it was wound around the big wheels on Colossus and read by a light box on the machine. Colossus, operated by girls from the Women’s Royal Naval Service, performed a statistical analysis of the tape by counting the patterns in the characters of the text and looking out for anomalies. The results – Colossus’s educated guess as to what the wheel settings were on the Lorenz that enciphered the message – were printed out and taken to the Tunny room to be tested.
The guesses of the wheel settings – Lorenz has 12 wheels compared with Enigma’s three to four – were tried out on Bletchley Park’s own interpretation of Lorenz, which looked nothing like the real thing because nobody at Bletchley had ever laid eyes one. A brilliant young mathematician called Bill Tutte guessed the inner workings of Lorenz purely by analysing a message Bletchley intercepted in 1941. Since BP didn’t even know what it was called, it named its version Tunny and all of its traffic Fish.
The Wrens (played by Vicky and I) plugged up the board at the front of Tunny according to the guessed wheel settings. Tunny was connected to a teleprinter machine and the original enciphered text was typed in. If plain, sensible German came out of the printer then the messaged had been cracked.
The first Colossus had 1,500 valves and came on stream at Bletchley Park in January 1944. It was first used to attack a Lorenz message on February 5 1944 and the more powerful mark two version, which had 2,500 valves, arrived days before D-Day in June that year.
Happy birthday Colossus!