166 | 15 THE wORlD’S fIRST COmPUTER OPERATORS
was a tricky operation, getting the tape to the right tension: it took a little time and had to be
done with great care. We were terrified of the tape breaking should the tension be wrong, as
breaks meant that valuable time was lost. (I can remember that when I was given a new Wren
to instruct, I was worried about leaving her for very long, and would hurry back from my meal-
break to make sure nothing awful had happened.) All the ‘break-ins’ that we put on the machine
were timed—they generally took about an hour to run. Every tape was logged on and off in a
book—the time that we had received the tape and the time that it was taken off the machine. It
was instilled into us that time was of the very essence. We knew that we were working against
the clock and that people’s lives depended on what we were doing.
We worked in four watches. I was on C watch, working from 9 a.m. to 4 p.m., 4 p.m. to 12
p.m., and 12 p.m. to 9 a.m.—a week of days, a week of evenings, a week of nights, and a week of
‘changeovers’. During this fourth week we filled in any gaps in A watch. The changeover week
could be very tiring—off at 9 a.m. and on again at 4 p.m., for instance. We had one weekend off
every month and an occasional additional weekend. Small buses took us between Woburn and
Bletchley Park: these would be lined up on the drive opposite the Mansion. Other destinations
included Gayhurst Manor and Wavendon.
A big block was put up to house two more Colossi. I was sent to work on Colossus 3 and my
friend Jean Beech was on Colossus 4. These stood in an enormous room, and were about twice
as big as Colossus 1. Later, Block H was built to house yet more Colossi.
I operated Colossus 3 alone under the direction of a mathematician codebreaker, or ‘crypt-
ographer’ as they were generally called, who would sit at a long table facing Colossus. Others,
such as Jack Good, Donald Michie, and Shaun Wylie, would come in to discuss what was going
on and to make suggestions. On the table in front of the cryptographer were sheets of codes
and he used a slide rule to make his calculations. He would tell me what he wanted from the
machine. I would pin up on the grid, at the back of the machine, whatever pattern he was
working on, and would put on the tape that he wished to run. At the front of the Colossus were
switches and plugs. We could set switches to make letter counts, and the machine had its own
electronic typewriter to record the results. Sometimes I was given a norm, and as each figure
came up on the typewriter I did a calculation and wrote down against the figure how much
above or below the norm it was. I became very good at mental arithmetic.
What I did not know then, but learned 50 years later, was that Colossus was designed to break
the messages sent by means of a machine called ‘Tunny’, which had been especially ordered
by the German High Command to enable them to communicate in complete secrecy. Hitler,
Göring, and Goebbels all used the Tunny machine, as did the field marshals and generals.
The Germans thought the coded messages sent out by the Tunny machines were completely
unbreakable. The Tunny wheel patterns were pegged up at the back of Colossus, and the tape
contained an intercepted message. The purpose of Colossus was to find the positions of the
codewheels at the beginning of a message.
If anything went wrong with Colossus we would contact the maintenance team. The officer
in charge of the team was an extraordinarily clever man, Harry Fensom, while another brilliant
engineer working with us was Ken Myers, who after the war worked on the coordination of
the traffic lights in London. The magnificent work done by these engineers has had little or no
recognition.
At the end of the war, we helped to break up most of the Colossi: this was a sad job. Then we
were made to sign the Official Secrets Act again. We all remained completely silent—until now.