Colossus Mark 1
Colossus Mark 1
On 6th June 1996 (the anniversary of D Day) HRH The Duke of Kent came back (to Bletchley)and formally switched on Colossus in the presence of its designer Tommy Flowers.

Photo: Colossus Rebuild Mark 1 © LSA Oct 1999.
| EXIT | Colossus Mark 1| Introduction |

Colossus was developed to break the coded messages which were generated by the German Lorenz SZ42 cipher machine, during the second world war. The encrpyted messages from the Lorenz were originally sent as morse code over the radio. The messages were intercepted by allied radio operators who would write down the morse code, which was later punched as Baudot teleprinter code, and fed into Colossus as a paper tape loop to be read by optical detectors at 5000 charaters per second!


Only two years after assembing the racking, by 1996 the Rebuild Team was able to  demonstrate the basic working functions of a Mark 1 Colossus, but only at a 2 bit level,  out of the five parallel bits coming from the paper tape reader. However, this was achieved without the J or K racks being fully wired and so it took almost another three years to devise the circuits and complete the very complex wiring.

Tony Sales writes "Now I turned to the paper tape reader and got that working on all five tracks, but not very reliably. So by 1999 we had repeated the 1996 results, but with signals now correctly routed through the switches on the J rack."

Thus by late 1999 the rebuild more closely resembled an original machine.

Towards the end of 1999, a sign above the rebuild declared "Colossus is Year 2000 Compliant"!

Colossus in 1999
Colossus (as seen in October 1999) is nearing completion.

"The tape-pulley system is complete and the paper tape runs up to speed and is easily scanned by the optical reader system. Two out of the five code elements are working, only another 3 circuit elements to duplicate!"

Photo: Colossus (Rebuild) © LSA Oct 1999.
Colossus viewed between the racks
Colossus viewed between the racks.

Photo: Colossus (Rebuild) © LSA Oct 1999.
Design, images and text compiled by © Light-Straw. Page last updated August 2015 revision. Checked May 2021.

All logos and trade marks are the property of their respective owners and are used on the Light Straw site(s) for review only. Students and researchers are recommended to make their own independent enquiries as to the accuracy of the information contained therein.