in the motor key. (There were never more than two consecutive dots in the motor
keys of those days). For in such a place, three consecutive letters of the
extended PSI key would be identical, and there would be only 32 possibilities for
corresponding trigrams of the plain language.
In the case of the first message, the PSI wheels were set by means of the
second method, but the first method was also used successfully later on.
(e) Foundation of Newmanry
When two or three messages had been set by the statistical method, it was
seen that new machinery, and a new section to operate it, was needed, for the hand
methods took far too long to be of much practical use. Mr. Newman was put in
charge of developments and his section came into operation later in the year.
This section set the X wheels of their messages essentially by the method
described above at first, but carried out its processes mechanically. The
technique of using only runs of form i + j was soon improved upon (see 23 of Part
(f) Statistical Chi-breaking
Statistical methods were carried further by the Research Section early in
1943 when an example of chi-breaking from rectangles was carried out. 'Wheel-
breaking' in the sense of chapter 25 was not used - in fact the message was so
favourable that all the chis were obtained from three rectangles, namely Delta-Z12
Delta-Z13 and Delta-Z45. The motor was obtained statistically.
Further investigation into Rectangling and other statistical chi-breaking
methods was carried out by the Newmanry, but it was only after the general
introduction of autoclave in Dec. 1943 that these methods were used operationally.
No statistical method for motor-breaking (with limitation) was developed by
the Research Section.
44C INTRODUCTION OF P5 LIMITATION
The autoclave was first used on a single link in March 1943, before the
Newmanry came into operation, but it was abandoned and was not used again until
December. The analysis of messages showing the autoclave effect was one of the
triumphs of the hand methods of statistical analysis.
The first sign that a new device was being used was the sending of a number
of pairs of messages on the 'Herring' link the members of each pair having the
same QSN number. These pairs should therefore have been depths, but attempts to
break them in the usual way all failed. Fortunately this happened in
the middle of the month, so the messages were expected to be using the name wheel
patterns as the earlier messages of that month, some of which had been broken.
One of the messages in the unbreakable 'depths' was about 6,000 letters long, so
the statistical method for setting X wheels was applied to it. The method was
completely successful. The de-chi was obtained and investigated. One passage of
this de-chi contained so many repeated letters that it looked like an extended PSI
key. The passage was
Z 3 D D D D V Y V N A A F G O O E 8 / / / K H R R R
Q Q Q C C C C 3 8 S S W M
It was assumed therefore that in the underlying clear