The Rebuild of Heath Robinson

Heath Robinson at Bletchley Park.



Heath Robinson was delivered to Bletchley Park in June 1943 and was first installed in Hut 11 which had been the original Bombe room for Turing Bombes, the machines used to break Enigma.

Harry Fensom and Alan Bruce were the two GPO maintenance engineers assigned to Heath Robinson. Two WRNS(Womens Royal Naval Service) ladies at a time were the operators and Jack Good and Donald Michie were the code breakers.

The first problem was teleprinter tape preparation. At least 2000 characters of cipher text was required, joined end to end to make a continuous loop. Then a similar length of Chi wheel patterns had to be punched up and arranged to be just one character longer than the cipher tape. This was to automatically change the relative wheel patterns by one position after each complete run through the tapes.

Then it was found that the optical readers in the Bedstead gave errors if a long stretch of adjacent holes or no holes occurred on the tapes. This meant adjustments to both texts to compensate for this.

A major problem was keeping the two tapes in synchronism at over 1000 characters per second. Originally the sprocket drive cogs were motorised but this proved impossible to sustain without tearing the tapes and a friction drive was used from the paper tape pulleys with the sprocket shaft just idling to keep synchronisation. This proved to be better but there was still a problem with tape stretching in the distance between the sprocket cogs and the optical reader aperture.


But Heath Robinson was the first machine to be used to assist in breaking Lorenz and despite all its problems and limitations it worked well enough to more clearly define the specification of an improved machine and this led to Colossus, but that's another story.

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