The work of Knockholt was the preparation of tapes and Red Forms (RF) for
Station X and consisted of (i) Interception (ii) Slip Reading (iii) Reperforation.
A tape with a single letter inserted or omitted in the middle would almost
certainly fail to set, hence the need for accuracy at Knockholt. Approximately
600 people were employed there. Nevertheless there were times when the traffic
ordered by us was more than they could handle. Once (Aug. 1944) an abortive
attempt was made to perforate tapes in Block F.
The priorities of ordering were decided by a morning meeting of various
interested parties in station X. This meeting also decided priorities for machine
setting and wheel-breaking. All ordering was done through the 'Control Officer' at
Station X by the following procedures:
A procedure Long tapes on unbroken days (according to a link priority list).
B procedure Other tapes for wheel-breaking ordered individually.
C procedure Tapes for setting on broken days.
D procedure Messages required for Crib purposes.
Depths The Control Officer was responsible for ensuring that these were
teleprinted at once.
33B TREATMENT OF TAPES
There were 30 receiving sets (in the Set Room). 26 covered priority links
and the rest were on directed and general search. Intercepted impulses were
automatically recorded on undulator tape and usually on printed and perforated
tape. The undulator tape was the most reliable and was used by the "slip-readers"
for improving the RF and perforated tape. In March 1945 efforts were made to save
time by using the automatic perforation (RAW TAPE) when interception conditions
were good. Blurred patches were marked by the operator. Sometimes dubious
portions were also slip-read. The method of raw tapes is a good one provided that
full slip-reading is continued until and if positive cryptographic results are
obtained with the raw tape.
Completely slip-read messages were passed to the reperforating room. The
final tape was checked against the RF with the use of a 'hand counter', though it
was not until Autumn, 1944 that a hand counter was issued to Knockholt.
Increased accuracy was immediately noticeable.
There were 10 transmission lines to our section. At its best the
reperforation room achieved an average daily output of 400,000 letters.
For further details, including auxiliary interception stations, the report