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| Ruth Bourne, aged 18, wearing her Wrens uniform. |
Of the 10,000-plus staff at the Government Code and Cypher School during World War II, two-thirds were female. Three veteran servicewomen explain what life was like as part of the code-breaking operation during World War II.
"I was given one sentence, 'We are breaking German codes, end of story'."
It was Ruth Bourne's first job out of college, when, like thousands of other young British women during World War II, she was recruited to aid the Allied cipher-breaking efforts at Bletchley Park.
Today, the mansion in the heart of the southeast English countryside is famous for being where the brilliant mathematician Alan Turing cracked the Nazi's Enigma code.
Because Turing's individual achievements were so momentous, it's sometimes forgotten that more than 10,000 other people worked at the Government Code and Cypher School, of whom more than two-thirds were female. These servicewomen played a pivotal role in an operation that decrypted millions of German messages and which is credited with significantly shortening the war.
The vital importance of preempting German plans led to a huge push to create machines that could crack ciphers at superhuman speeds. These efforts produced Colossus, the world's first programmable electronic digital computer.
However, the reality of running these electromechanical machines, setting rotors and plugging boards day in day out, was often less than thrilling, with the 18-year-old Bourne envying the girls who test-piloted aircraft fresh off the production line.
"That was exciting but standing in front of a machine for eight hours was not," she said.
As mundane as her daily routine was, it was vital in deciphering coded messages sent by the German army, navy and air force and helping the Allied forces turn the tide of war.
The problem facing Britain and its allies early in the war was that the Enigma machine used to encrypt Nazi military traffic could scramble a message in 158 million million million ways, and each day the settings used would be changed. On top of that, on an average day at Bletchley Park code-breakers were tasked with breaking between 2,000 and 6,000 messages of German, Italian, Japanese and Chinese origin. There were far too many to check by hand.
The code-breaking needed to be automated, and it fell to British mathematician and father of the computer Alan Turing, with the help of the British Tabulating Machine Company, to devise the machine for the job.
His solution was the Bombe, an electromechanical machine designed to emulate the workings of 36 Enigmas.
Bourne was a member of the Women's Royal Naval Service, known as the Wrens, who were charged with preparing the machines each day, turning the drums on the front and plugging up the boards at the back according to settings laid out in a menu. These settings were derived from cribs, which were best guesses at fragments of plain text—for example, standard openings such as weather reports—from the enciphered messages.
If correct, these cribs would reveal some of the Enigma settings used to encode the message and provide a starting point for devising the remaining settings. The Bombe could check the possible ways the Enigma could have been set up incredibly rapidly, dismissing incorrect settings one at a time.
If the crib and initial settings were good, then the Bombe could return the information needed to crack the code within minutes.
"I joined just around D-Day and at that time the traffic was tremendous. We were breaking thousands of messages," Bourne said.
"We knew that every 24 hours the code was changed and that was why time and accuracy were of the absolute essence. You were really pressured."
Like Bourne, many of the Navy Wrens operating the Bombs were teenagers not long out of school, who found themselves working a punishing schedule, with very little margin for error.
Bourne said, "You didn't have to be rocket scientists but what you had to be was 125 percent accurate. You worked in pairs and you and your checker would plug up the back of your machine, which was extremely complicated. You had to brush out the wires on your drums so there wouldn't be short circuits, make sure the plugs at the back of the machine were pushed in and straight, and you had to be on the go for the eight-hour shift, as you were standing for the whole time."
There was little respite during a shift for the Bombe operators, even during meal times.
"You had half an hour off for a meal," said Bourne. "The Bombs were in a building with high brick walls, barbed wire and sentries, you had to get out from there, run to your canteen, grab your meal and run back and then your checker, who'd been operating while you were away, could go and get her meal. It was very intense and very concentrated. We were young and learned quickly."
The high-point of the day was getting a "Job Up" message, as it meant that their machine had broken a code, but she was always conscious one mistake could wreck their chances.
Bourne said, "You were a link in the chain and you couldn't be the weakest link. If you'd made a mistake on your machine—you hadn't pushed a drum on properly or you'd put a plug in incorrectly—and the machine wouldn't work, you would get a reprimand, 'If you had been more accurate, we might have brought the job up'."
Adding to the stress were the working conditions. Bombe operators worked round the clock, with teams spending one week working 8am to 4pm, the next 4pm until midnight and then midnight to 8am after that.
"The main pressure was the changing of the shifts, because you were always jetlagged. Your body clock was all over the place. I found it very hard to sleep during the daytime as there were not really proper blackout curtains, they were very flimsy and thin," said Bourne.
Outside this serious work, however, Bourne and her fellow Wrens were pretty normal teenagers, with similar preoccupations to those of young people today.
"We had two lives really," Bourne said. "One where you were in your workstation and you knew your Bombe machine was ticking over and you brought a job up. But outside that it was being a normal girly in the Wrens. 'Who were you dating tonight? Where have you been? Are you going dancing in Covent Garden?' That kind of thing."
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