By 1959, the last of them were gone. Around 211 Bombe machines had been built to break the German Enigma cipher, and on Winston Churchill’s orders every one was eventually reduced to scrap—drums, relays, miles of wiring, the whole apparatus melted down for the metal. The women who had spent their war running these machines went home forbidden by law to say a word about it, in many cases not even to the men they later married.
They had signed the Official Secrets Act on the day they arrived, and the obligation did not lapse when Germany surrendered. For roughly thirty years, a generation of operators carried the most important thing they had ever done as a blank space in their own biographies.
What the Bombes Actually Did
The Bombe was an electromechanical device, designed in 1939 by Alan Turing and refined the following year by Gordon Welchman, with the engineering handled by Harold “Doc” Keen at the British Tabulating Machine Company in Letchworth. It built on earlier Polish work—the bomba kryptologiczna devised by Marian Rejewski before the war—but the British version was a far larger and more capable machine.
It was not, strictly speaking, a computer. It ran through the enormous number of possible rotor settings an Enigma operator might have used on a given day, eliminating those that produced logical contradictions and surfacing the small handful of candidate settings that codebreakers could then test by hand.
Each Bombe stood about seven feet tall and weighed roughly a ton, its front face carrying 108 rotating drums arranged in 36 sets of three, each set mimicking the wheels of a single Enigma. When the machine found a setting that did not contradict itself, it stopped with an audible clatter, and the operator recorded the position before resetting the drums and starting the next run.
The first Bombe, code-named Victory, began work in March 1940 in Hut 11 at Bletchley Park. The intelligence it helped produce, codenamed Ultra, fed directly into Allied decisions, and at peak the machines were decoding thousands of messages a day.
The work itself was repetitive, physically demanding, and conducted in heat thick with the smell of hot oil and electrical insulation. Historians credit the wider codebreaking effort with shortening the war by an estimated two years.
The Women at the Machines
By the end of the war, almost 1,676 women of the WRNS and 263 RAF personnel were deployed across the 211 Bombe machines spread between Bletchley Park and its outstations at Stanmore, Eastcote and elsewhere. Most of the operators had been recruited in their late teens or early twenties.
The machines were organised in bays, each bay named after an Allied country and each individual Bombe after a city—an operator might spend a shift working a machine called Oslo or one called Madrid, as former Wren Jean Millar recalled of her time at Eastcote. They worked in pairs, one at the Bombe and one in the checking room, through rotating eight-hour shifts around the clock.
On arrival they signed the Official Secrets Act and were told only that the work was vital. Detail came sparingly, if at all. Ruth Bourne, who operated Bombes at Eastcote and Stanmore from 1944, later said she never even heard the name Enigma until long after the war.
The pressure to be exact was relentless. A single transcription error could waste the work of the cryptanalysts upstream, and the operators were drilled accordingly. Few of them learned what their machines had actually achieved until the war was nearly over.
Why the Secrecy Outlasted the War
The destruction of the machines and the lifelong silence demanded of their operators were not paranoia. The techniques used to break Enigma remained militarily valuable long after Germany’s surrender, and Britain had concrete reasons to keep them hidden.
Variants of the Enigma machine were sold or passed on to governments around the world in the post-war years. Those governments believed their communications were secure; Britain had no interest in telling them otherwise. Keeping the Bombe’s existence secret was, in effect, a continuation of the war by quieter means.
So the obligation imposed by the Official Secrets Act did not end with the fighting. For decades the operators were forbidden from telling anyone—parents, spouses, children—where they had spent the war or what they had done there.
The embargo on the wartime work was not lifted until 1974, and even then almost nothing was revealed about the machines themselves or the specific tasks they had performed.
The Order to Destroy Them
At the end of the war, Churchill ordered the Bombes destroyed so the technology could not fall into the wrong hands. He took a personal interest in the operators’ work; a telegram of his that was pinned up at Eastcote read, “Glad to hear the hens are laying so well without cackling.”
The women did much of the dismantling themselves, attacking their own machines with soldering irons and feeling little sentiment about it. The drums and wiring, which had drawn on thousands of suppliers and components to build, were pulled apart and carted off as scrap.
For years it was assumed every machine had been broken up at once. In fact, around 50 Bombes and 20 Enigma machines were quietly retained, overhauled and stored away in case they were ever needed again.
According to the GCHQ documents that later surfaced, those retained machines were not finally broken up until 1959, by which point the rise of electronic computers had made the old electromechanical technology obsolete. That is the date on which the last of the Bombes truly disappeared.
The Cost of Silence
For the women who had operated them, the silence imposed a peculiar loneliness. They returned to a post-war Britain in which men spoke openly of their service and women were quietly steered back toward domestic life, with no easy way to explain the strange gap in their histories or the technical fluency they had somehow acquired.
In the accounts many of them gave decades later, the secrecy carried ordinary, grinding costs: a stretch of years that could not be described, skills that could not be claimed, a war that had to be summed up, if at all, as something duller than it was. The most important work of their lives had, officially, never happened.
When the secrecy was relaxed in the mid-1970s, after F. W. Winterbotham’s The Ultra Secret appeared in 1974, many of the operators were already grandmothers. Some took the secret to their graves without ever telling their families what those years had actually involved.
The working Bombe you can see today is not one of the originals. It is a reconstruction, built over years by a team of volunteers and now on display at The National Museum of Computing, on the Bletchley Park estate—assembled from fragments of documentation released decades late and the recollections of surviving operators, memories that, by the time they could legally be shared, had been carried in silence for thirty years.
Switch it on and it still clatters and stops the way the wartime machines did, drums spinning down to a halt in a room that smells faintly of warm oil. The machines the women actually touched are gone—melted, poured off, folded back into the metal supply of a recovering country. Most of the women were gone too, or very nearly, by the time anyone was finally allowed to say what they had done.