Editing Colossus computer (section)

==Operation==
[[File:Colossus computer selection panel.png|right|upright=1.35 |thumbnail |Colossus selection panel showing selections amongst others, of the far tape on the bedstead, and for input to the algorithm: Δ'''Z''', Δ<math>\chi</math> and Δ<math>\psi</math>.]]
The Newmanry was staffed by cryptanalysts, operators from the [[Women's Royal Naval Service|Women's Royal Naval Service (WRNS)]] – known as "Wrens" – and engineers who were permanently on hand for maintenance and repair. By the end of the war the staffing was 272 Wrens and 27 men.{{sfn|Good|Michie|Timms|1945|loc = 1 Introduction: 15 – Some Historical Notes, 15C Period of Expansion, (b) Colossus, p. 35}}

The first job in operating Colossus for a new message was to prepare the paper tape loop. This was performed by the Wrens who stuck the two ends together using [[Bostik]] glue, ensuring that there was a 150-character length of blank tape between the end and the start of the message.{{sfn|Good|Michie|Timms|1945|loc = 5 Machines: 53 Colossus 53A Introduction, p.333}} Using a special hand punch they inserted a start hole between the third and fourth channels {{frac|2|1|2}} sprocket holes from the end of the blank section, and a stop hole between the fourth and fifth channels {{frac|1|1|2}} sprocket holes from the end of the characters of the message.{{sfn|Flowers|1983|pp=241, 242}}{{sfn|Good|Michie|Timms|1945|loc = 5 Machines: 53 Colossus 53B The Z stream, p.333}} These were read by specially positioned photocells and indicated when the message was about to start and when it ended. The operator would then thread the paper tape through the gate and around the pulleys of the bedstead and adjust the tension. The two-tape bedstead design had been carried on from Heath Robinson so that one tape could be loaded whilst the previous one was being run. A switch on the Selection Panel specified the "near" or the "far" tape.{{sfn|Fensom|2006|p=303}}

After performing various resetting and zeroizing tasks, the Wren operators would, under instruction from the cryptanalyst, operate the "set total" decade switches and the K2 panel switches to set the desired algorithm. They would then start the bedstead tape motor and lamp and, when the tape was up to speed, operate the master start switch.{{sfn|Fensom|2006|p=303}}