TNMOC Blog IV – Colossus

Colossus, the first large-scale electronic computer, was used against the German system of teleprinter encryption known at Bletchley Park as ‘Tunny’.

The significant achievement in computing terms of Colossus was the decision to move from a mechanical relay switch counting system to a fully electronic valve system, whose only moving part was a beam of electrons. The concepts in operation lay the foundations for the digital electronic computing revolution. However, there are still many mechanical parts in action on Colossus including the 5000rpm tape wheels and the initial calculation relay switches on the front panel of the gigantic machine.

Stepping into Block H, the original site of Colossus MKII 9, where the reconstructed Colossus exists today is probably a bit of a different story to its wartime operational environment. The machine is encircled by a steel and glass barrier, to protect not just the machine, but the visitors. Chief Engineer Phil Hayes informed me of how the valves can run up to 400 Volts. The machine itself operates faultlessly on a day to day basis at the museum, constructed out of original (or at least authentic) components; it is a marvel to the engineers who designed and built the original machines between 1943 and 1945.

The cold atmosphere in the room quickly warms up as Phil starts to engage the machine. Turned off over night in this museum piece format, the original functional machines were left to run 24/7 in concurrence with chief designer Tommy Flowers’ discovery that so long as valves were switched on and left on, they could operate reliably for very long periods, especially if their ‘heaters’ were run on a reduced current. The space of Block H would have been furnace like at times. One can see from the few archived photographs of the WRNS (Wrens) who operated the machine, how they were permitted to work with sleeves rolled up, battling the temperature inside the enclosed and most top of all top-secret environments. A switchable secondary tape roll was attached so new encrypted messages could be loaded up to reduce downtime between decrypting messages and ensure efficient operation. There was no need to stop unless technical developments were to be made.

Upon my visit to Block H, I was fortunate enough to hear Colossus go from idle to fully functioning, actively decrypting a tape message containing an authentic teletype message sent between posts of the German High Command. The sounds of the machine are more reminiscent of an industrial age than of the silicon based devices that occupy our digital computing world today. Certainly the clunking sounds of magnetic relay switches, the thudding shudder of a teleprinter output, the whine of 5000rpm motors and the sizzle of friction between wheel and paper tape are unlikely to be heard in the evolution of computing again but it’s here that the on start of a new generation of data controlling devices was born, and without even a modest fanfare for the triumph of engineering that occurred within the dense, blast proofed concrete confines of Block H, at Bletchley Park, now The National Museum of Computing.

“It is regretted that it is not possible to give an adequate idea of the fascination of a Colossus at work; its sheer bulk and apparent complexity; the fantastic speed of thin paper tape round the glittering pulleys; the childish pleasure of not-not, span, print main header and other gadgets; the wizardry of purely mechanical decoding letter by letter (one novice thought she was being hoaxed); the uncanny action of the typewriter in printing the correct scores without and beyond human aid; the stepping of the display; periods of eager expectation culminating in the sudden appearance of the longed-for score; and the strange rhythms characterizing every type of run: the stately break-in, the erratic short run, the regularity of wheel-breaking, the stolid rectangle interrupted by the wild leaps of the carriage-return, the frantic chatter of a motor run, even the ludicrous frenzy of hosts of bogus scores.”

Good, Michie & Timms 1945, p. 327 in 51. Introductory: Impressions of Colossus


RCA AR-88LFI spent some time working through the process used to decrypt the cipher made by the Lorenz SZ40/42 in-line cipher machine used by The German Army in World War II. These were messages that came from the German High Command. High level stuff.

It’s a fascinating story of incredibly high level skill in logical analysis and something I couldn’t do justice describing myself. I recommend a visit to TNMOC to find out more. I’ve started off at the point of entry… The Radio Frequency transmission of wireless telegraphy.

I’ve recorded many sounds from the RCA AR-88LF at the museum, covering as many sonic aspects that I can. Here is a little teaser of a recording taken from the rear of the unit, picking up super low electromagnetic frequencies.

TNMOC Blog I – Mechanical Calculators

Documenting Desktop Mechanical Calculators

Vintage III - Mechanical Calculator

I have been busy making a detailed audiovisual archive of the below mechanical calculators at The National Museum of Computing, Bletchley Park as part of my project The Imitation Archive.

Trinks~Triplex - Mechanical Calculator Vintage II - Mechanical Calculator

I am going to be working on creating audiovisual archive material for the next month. This is my first post. A series of simple images of mechanical calculators, all of which have a similar aesthetic to them, by and large but from different manufacturers. A variation of a theme. Vintage - Mechanical Calculator Klowther 400 - Mechanical Calculator

These are common devices used pre-computing. They are the original data processors. Moving on, I will begin to investigate the calculation power of electronic counting machines (early computers) and will continue to post audiovisual material as I progress through the collection. Facit - Mechanical Calculator Contex - Mechanical Calculator Brunsviga II - Mechanical Calculator Brunsviga - Mechanical Calculator

The Imitation Archive is a residency project with The National Museum of Computing, with support from The Arts Council England, The British Library and Birmingham Conservatoire.

High definition audio and further commentary coming soon.

Photos in order of appearance:

Bell Punch Company Limited
Model No. 509/D/865.686

Grimme, Natalis and Co.
Model Name. System Trinks-Triplex

Monroe Limited
Model No. Unknown

The London Computator Corporation Limited
Model No. LC/509/SF/392

The London Computator Corporation Limited
Mode No. LC/512/SF/158

Atvidaberg Facit
Model No. C1-19
Serial – 522373

Model No. 136557
Model Name. – +-x

Grimme, Natalis and Co.
Model Name. Brunsviga 13ZK
Serial No. 220217