This is a strictly functional and non-technical account of the machines
used. A technical account is to be prepared by the post office engineers.
Some attempt is made to avoid statements technically false, but none to
avoid statements technically vague.
The terminology is that of the layman and cryptographer: for example a
switch means a lever to be pushed up and down, or a knob to be rotated. As in
other parts of the report, an impulse means one of the five streams of which
teleprinter letters are composed, but when the meaning is clear from the
context, impulse is also to mean electrical impulse, otherwise called pulse to
(c) Scope of the chapter.
Such history as is included is a description of development and lacks
Colossus and Robinson receive detailed treatment, for in large measure it is
the use of these machines which gives Tunny-breaking its distinctive character.
Copying machines are indispensable but less distinctive, and are treated
The specialized counting machines, Dragon, Aquarius, Proteus are treated
rather sketchily because being specialized most of their functions are adequately
dealt with in the description of their applications.
(d) Relative importance of machines
The pre-eminence of Colossus and Robinson is manifest.
The need for a "Tunny" machine to decode messages, or, as an intermediate
step towards decoding, to de-chi them, is obvious.
The need for efficiency in other copying machines is apt to be overlooked;
one of them, Miles, was in fact unduly neglected: in particular the production
models of Miles A were vetoed. The supply of spare parts for readers and
reperforators generally has been inadequate. The hand counter is very simple and
quite indispensable: a long time elapsed before a reliable one was produced. The
amount of Colossus time wasted because tapes were delayed or incorrect is
difficult to estimate but it is certainly very considerable.
(e) Electronic counters etc.
As a matter of general interest it may be mentioned that on the existing
counting and stepping machines, counting is in the scale