The Colossus Rebuild Project by Tony Sale

Colossus Reborn

Paper Tape Preparation

Preparation of punched paper tapes was a real problem in WW II and is still a problem now.

There are no surviving paper tapes so they also had to be recreated. I obtained, by rather clandestine means, one printout of a WW II cipher text/plain text pair together with wheel patterns and start positions. I used this to verify a simulation of the Lorenz cipher machine written in Q basic. I circulated this simulation to some of the WW II Colossus engineers and to Donald Davies who had studied Lorenz and the Siemens machine. We eventually agreed on a version which we all thought gave a true representation of the Lorenz machine complete with all limitations.

I also received from GCHQ archives a long decrypted Tunny multipart message. I re-keyed this text and used the Lorenz simulator to encipher it.

I now had two lengths of cipher text to try on Colossus.
But first I had to punch these cipher texts to paper tape. Over the years I had acquired various pieces of post war hardware. Among these was a high speed paper tape punch. My colleague, John Sinclair, made an interface box to a PC Line printer port and we could now go from PC to paper tape. But not quite, there was a mapping to be done from ASCII characters to the 5 hole Baudot code character set on the tape. Another Qbasic program and we were in business.

Each tape had to be connected end to end to make a loop with about 4 feet of blank tape between the end and start of cipher text.

Special holes have to be punched between tracks 4 and 5 for "stop" and between tracks 3 and 4, "start". The WRNS in WW II had a special holder and punch for doing this. I managed with a post war "unipunch", a one hole punch for correcting tapes.

This page was originally created by the late Tony Sale, the original curator of the Bletchley Park Museum, and Secretary of the Bletchley Park Heritage Society.