The Newmanry History

52 Page 330

These were added shortly after Colossus 2 came into use, and afterwards

Colossus rectangling has been slightly disappointing; although the

Colossus was designed for chi and psi setting, not for breaking. The first

That Colossus (including Colossus 1) should prove suitable for wheel

(i) Longer bedsteads, because breaking requires longer

texts than setting.

(ii) Uncertain letters replaced by 9's are a nuisance in

chi-setting and breaking from cipher, even if there
is no slide, but it is in chi-breaking from depth
key, where missing letters are a substantial part
of the text that the problem becomes acute. It was
found necessary to use the Q panel for the condition
Z not = 9 , there being no "not" facility on the plug-
board, and plugging all runs, which was intolerably
tedious.

In consequence "not 9" was fitted, a device which
imposed Z not = 9 but this lost all genuine 9's also
(about 1/17 of the text after differencing), and was
replaced by "not 99".

(iii) Multiple testing on doubted wheels is obviously

of great value when setting long messages during
wheel-breaking.

(iv) Intolerable delays and mistakes during wheel-breaking

were caused by the need for setting up pins at the
back of Colossus and complaints finally extorted
the wheel-breaking panel on the front of some machines.

The clamour for specialised gadgets continues : the objection to it is

Colossus soon replaced Robinson for setting and breaking, but Robinson

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