Circulation of material in the Testery was arranged from Room 12 with the
help of the de-chi clerk (in Room 41) who kept track of material in Room 40 and 41
and the Supervisor, who kept track of material in the decoding room. Documents for
each message worked on in the Testery were circulated in an envelope which
included the Red Form (but not the tapes). When the message had been decoded, it
was returned to Room 12:
Cryptographers in the Testery were divided into two rooms, the so-called
Breakers in Room 41 and the so-called 'Setters' in Room 40. Room 41 numbered 5 on
a shift plus 4 on permanent days, and Room 40, 8 a shift. Room 41 contained the
more experienced men and the Head of Room 41 was responsible for all work in the
section, on his watch.
The growth of the Testery and the division of work has been established in
14A( b). The purpose of this chapter is to describe the organisation in 1945 when
there were two major cryptographic commitments.
(1) Recovery and Solution of Key from Depths.
(ii) Psi and motor setting from a de-chi by hand or with the help of Dragon.
Possible depths noticed at Knockholt were teleprinted at once, not more than
1000 letters being sent. When the interception registers arrived in Room 12 they
were carefully examined and a list of other possible depths sent to Knockholt.
Before being issued to the Head of Room 41, the annotations "Pause", "Auto"
and "Hand" were copied by the de-chi clerk from the Red Form on to the de-chi. The
head of shift saw that the de-chis were worked on in a suitable order and that
psi breaking jobs were given suitable priority. Various aids to de-chi "breakers"
existed in the form of decodes and abstracts of message characteristics.
De-chis were passed to Room 40 when sufficient P and PSI had been obtained
to set or break the psis at some point in the de-chi. Room 40 found the settings
for the start of the message and worked out sufficient extended psi to set the
motor or break the motor patterns. In the most favourable circumstances jobs took
20 minutes and 1 1/2 hours respectively, but more usually rather longer owing to
unfavourable motor wheels or slides in the text. Messages with X2 limitation were
sometimes set at the position of the Room 41 break and worked back on a specially
De-chis worked on in Room 41 without success and any unworked setting de-
chis on low dottage days could be sent to Dragon, which was under the control of
members of Room 41. When ???19 (Note: illegible) it was general practice to send all de-chis to
Dragon. A few de-chis were returned to the Newmanry for motor runs.