At first glance, even second glance, Bletchley Park could easily be just another beautiful British building deserving of some loving care and attention. But for many years its walls guarded one of the best kept secrets of the 20th Century. During the Second World War it was the top secret home to the cryptanalysts, mathematicians and military personnel later credited with shortening the war by at least two years and saving millions of lives by breaking the secret ciphers used in Nazi communications. Seventy years after war was declared on Germany, Gizmag takes a closer look at what went on at HMS Pembroke V, the people who worked there and talks to some of the those now dedicated to ensuring that its legacy lives on.

Situated 50 miles to the North West of London, Bletchley Park was originally built in the early 1880s by London financier Sir Herbert Samuel Leon. It remained the family home until the death of Sir Herbert's wife in 1937 when the estate fell into the hands of property developers. Keen to cash in on a growing need for housing, the buildings making up the estate were scheduled for demolition. War, however, was to prove its savior.

Towards the end of the 1930s Hitler was gaining power on mainland Europe and the threat of all out war was imminent. London was not a safe place to be and a new home was needed for the Government Code and Cipher School. Luckily there was a vacant property situated right at the center of major road, rail and communications networks in the UK. No doubt to the great disappointment of the developers, Bletchley Park got its call-up papers and the first codebreakers began to arrive in August 1939.

The enigma of Enigma

To encode messages sent between military personnel, the Germans used a device which was believed to produce unbreakable codes, the Enigma cipher machine. Originally invented in 1918 by Scherbius & Ritter, its military potential wasn't realized until 1925 when the Germans began making a few enhancements to make encoded messages even more secure.

By the late 1930s, the German military had settled on a three rotor from a possible five configuration combined with the Steckerbrett plugin board. Each rotor had 26 input and 26 crosswired output contacts and could be configured in 17,576 different ways. The rotors were arranged adjacently along a center spindle.

As the operator keyed in a message, electrical signals would flow through the wiring and instruct a rotor to produce a corresponding coded letter. Unless the resulting message was being read on a machine configured in exactly the same way, the encoded text appeared as utter gobbledegook.

According to the National Centre for Excellence in the Teaching of Mathematics: "the odds against anyone who did not know the settings being able to break Enigma were a staggering 150 million, million, million to one."

The Polish breakthrough

Unknown to the Germans however, Polish mathematicians had managed to overcome the device's complexities and successfully decipher the military Engima messages by the end of 1932. At that time, machine configurations were only being changed once every few months giving analysts plenty of time to crack the codes.

As Hitler's campaign in Europe began in earnest, the changes were made ever more frequent until daily configuration schedules were drawn up which effectively locked out the Polish decoding effort. Prior to the invasion of Poland in 1939, the Polish Cipher Bureau shared its decoding intelligence with the French and British, even offering an Enigma simulator made in a Polish factory - Marian Rejewski's Bomba Kryptologiczna.

The British Bombe

Using the Polish intelligence and sample machine as a starting point, noting that a typed letter could never be encrypted as itself and adding in other clues and intelligence provided by analyzing intercepted transmissions supplied by listening posts all over the UK and Europe, code-breakers at Station X or HMS Pembroke V (both umbrella codenames for Bletchley Park and its substations) were again able to crack the code.

Brilliant mathematicians Alan Turing and Gordon Welchman improved on the concepts originally offered by the Polish Cipher Bureau and developed a bigger, more powerful machine to significantly reduce the time taken to decode German Enigma-encoded transmissions. The British Bombe weighed a ton and stood six feet six inches high, two feet deep and seven feet long.

Each machine consisted of rows of rotors at the front and wiring panels at the back and could calculate the possible settings for 36 Enigma machines. As the Bombe rotors whizzed round, if any of the sets stopped then the starting positions on a German Enigma had been found and the configuration was reported down the line by the members of the Women's Royal Naval Service (WRNS), who operated the machines for 24 hours a day over three shifts.

At the height of the secret decoding operation, some 200 or so Turing-Welchman Bombes were in use at Bletchley Park and its substations. Whereas the Polish Bomba machine "depended upon the very particular way the Germans had been using the Enigma", notes Andrew Hodges (author of Alan Turing: the Enigma) the British Bombe was a "far more powerful device, capable of breaking any Enigma message where a small portion of plain text could be guessed correctly. From late 1940 onwards, the Turing-Welchman Bombe made the reading of Luftwaffe signals routine."

The birth of computing

Communications between German High Command and top-ranking officials were exchanged using a much more complex machine than Enigma, the Lorenz. This machine used the International Teleprinter Code and encrypted its messages using a dozen rotors. Each letter of the resulting output was followed by a series of seemingly random letters. Just like Enigma before it, the breaking of the Lorenz code depended on discovering the starting position of the rotors.

Using statistical analysis and a fair amount of brain power, John Tiltman managed to decode Lorenz messages by hand in 1941 but a few short years later the Germans introduced variations which made decoding by hand impossible. Dr Max Newman and his team set about developing a machine to speed up and automate the process of finding the settings used for each message and so break the new Lorenz codes.

The first machine to be built - affectionately named the Heath Robinson to honor the illustrator and eccentric machine designer - proved too slow and unreliable but at least served to prove that automation was possible. Newton solicited the help of Post Office electronics engineer Tommy Flowers who spent 11 months designing and building Colossus.

Colossus Mark I contained some 1500 valves and was delivered to Bletchley Park in December of 1943. Flowers was already working on the Mark II when the first machine was switched on in January 1944. The Mark II contained many more valves and could read paper tape input at 5000 characters per second meaning that the complicated statistical analyses and mathematical calculations required to crack Lorenz-encoded messages could be undertaken in hours rather than weeks. Nine new Mark II's were built and the Mark I upgraded. Colossus was essentially the world's first digital, programmable electronic computer.

Thankyou and goodnight

Deciphering work using the Bombe and Colossus machines continued until August 1945 when Japan surrendered. Winston Churchill (who called the staff involved in the work at HMS Pembroke V the "Geese that laid the Golden egg and never cackled") ordered the complete destruction of the war machine's best kept secret. Not a shred of evidence was to be left that could give any indication of what went on at Bletchley Park and its substations.

And so machines were dismantled, documents destroyed and the 9000 or so tight-lipped staff dispersed. Some continued secret code-cracking work at the Government Communications Headquarters (GCHQ) and others returned to normal life, those around them blissfully unaware of the contribution they had made to the war effort. Bletchley Park became home to a variety of training schools for teachers, government officials and engineers.

Keeping mum

In the years that followed, the cipher work at Bletchley Park, for the most part, remained under wraps. Then in 1974 a book appeared called The Ultra Secret by Captain F.W. Winterbotham. According to those who actually worked there it was not entirely accurate but for the first time revealed some details about the secret wartime coding operations at Station X. It also meant that ex-operatoves could at last point to something and say "that's what I did during the war"!

Bletchley Park was finally released from its association with British Intelligence in 1987 and decommissioned. By 1991 the site was almost empty and again the threat of demolition loomed, the true scale and secret nature of the vital work carried out within its grounds working against it. Learning of its fate, a local archeological and historical society held a farewell event in October 1991 which was attended by over 400 of Bletchley Park veterans.

Opening up the past

At the eleventh hour the local volunteers decided to try and save the site from demolition. Negotiations with the owners were opened by the newly formed Bletchley Park Trust and the local Borough Council declared most of the estate a conservation area. With the help of enthusiasts, volunteers and ex-workers, the Trust created an exhibition documenting the Park's vital role in the war effort. The doors to the Bletchley Park Museum were officially opened by HRH The Duke of Kent (who also became its chief patron) in July 1994.

The threat of redevelopment continued to bubble under the surface though until a deal with the owners was reached whereby the Trust was given a long-term lease and the Park's future made slightly safer.

Rebuilding the machines

Building the Bombe

In 1998 an appeal for help appeared in an edition of the Computer Conservation Society magazine. AutoCAD users were required to produce technical drawings so that a rebuild of the Turing-Welchman Bombe could be attempted. Although three Bombes survived the dismantling process they were scrapped in the 1960s, John Harper of the volunteer rebuild team recalls "we had individual component drawings returned to Bletchley Park by GCHQ but no assembly drawings. These were created before we started making the machine with the help of people who had worked on the Bombe together with photos recovered from archives."

Some 900 drawings later and the team set about manufacturing the parts needed for the project, a daunting task for such a small team - "the sheer number of some of the parts we have had to make is mind boggling. For example, there are over 12,000 studs needed in the commutators and over 18,000 drum brushes. Something of the order of 50,000 cable terminations on nearly twelve miles of red wire were made. Around 17,000 screws of varying sizes hold the machine together."

After almost a decade of tireless dedication, HRH The Duke of Kent returned to Bletchley Park to officially switch on the rebuilt and fully working copy of the British Bombe in July 2007.

Colossus reborn

Tony Sale was one of the original Bletchley Park campaigners from the early 1990s and at that time was working at the Science Museum in London restoring computers. He began to toy with the idea of rebuilding Colossus, the grand-daddy of digital computing.

Using EasyCAD software on a 486 computer, the first machine drawings were created from old photographs and the very few circuit diagrams he had managed to find. The original designer of the paper tape reader system, Dr Arnold Lynch, was brought on board and in 1994 work on building the frame began in the very room where one of the great machines had stood during the war at Bletchley Park.

Many original component parts were successfully sourced thanks in part to the digital overhaul of old telephone exchanges, as well as rummaging through the dusty shelves of various vintage radio dealers. The project team expanded as more volunteers offered help and by mid-1996 there was enough of the machine in working order for a Royal switch-on by HRH The Duke of Kent. Also present was the machine's original creator, Dr Tommy Flowers.

Spurred on by this early success, Sale and the team decided to upgrade the rebuild to a Mark II machine. Aided by more detailed information released under the Freedom of Information Act in the US and after overcoming a few setbacks, the team managed to recreate a fully working Mark II Colossus in time for the 60th anniversary of the first running of a Colossus Mark II in Bletchley Park.

Campaigns, Twitter and modern computing

After visiting Bletchley Park in April 2003 as Chair of the British Computer Society's Women group (which she founded in 2001 to provide support for female IT professionals), Dr Sue Black became a passionate supporter of the work undertaken by the Bletchley Park Trust.

As well as securing funding for the recording of interviews with some of the women who worked there during the war, the Head of the Information and Software Systems Department at the University of Westminster's School of Electronics and Computer Science also set about helping to raise awareness and funds for vital repairs.

"It is the birthplace of computing as we know it, the Geek Mecca and also the place where the major codebreaking was done that shortened WWII by two years saving millions of lives. What place in the UK is more important?" She "started blogging about the campaign so that there was somewhere that I could point to where people could find out all about the campaign and then hopefully get involved."

Bletchley Park is also home to the National Museum of Computing, which shows the development of computing from the pioneering days of Colossus right up to the products and systems in use today. It represents "the UK's only hands-on exhibition of computing hardware and software technology. It traces the development of the computer from its origins with the Colossus, through the mainframes of the 1960's, mini computers, homebuilt micros to the PC's of today. The vast majority of our exhibits are fully operational and you can come and play with the computers you remember from years ago or discover something new."

The Park continues to embrace new computer technology, with museum workers, volunteers and supporters regularly using micro-blogging site Twitter, social networking sites such as Facebook and photo sharing site Flickr to help raise its profile.

Supporters on Twitter now regularly meet in the guise of the Station-X geek meets to exchange ideas, discuss campaign updates and plan future strategies or just to learn about the Park and to talk to fellow supporters - using more than 140 characters.

Brit Twitter King, Stephen Fry being shown an Enigma machine at Bletchley Park earlier this year:

The future of Bletchley Park

The public profile of Bletchley Park and those who worked there is beginning to see some limelight, no doubt helped by recent press interest following the apology issued by UK Prime Minister Gordon Brown in September for the appalling way Alan Turing was treated after being prosecuted and convicted of homosexuality in 1952 (rather than serve a prison sentence, Turing agreed to experimental chemical castration. No longer allowed to work at GCHQ and even considered a security risk, he subsequently took his own life in 1954).

Other recent events of note include visits by computer pioneer Sir Maurice Wilkes, Foreign Secretary David Miliband and the BBC (in the form of the Antiques Roadshow).

But despite all this recent attention its future remains uncertain. The Trust hopes to build on recent successes and turn the Park into a world class heritage center but funding worries threaten to put the brakes on these ambitious plans.

According to the Park's Kelsey Griffin, the Bletchley Park Trust: "has come a very long way in that it can now balance its budgets but its finances still quiver on a knife-edge. " The Trust has recently benefited from financial assistance from English Heritage, Milton Keynes Council and was recently awarded lottery funds to help develop the museum. In order to secure the latter though, £1 million must be found to match-fund the bid. Griffin explains: "In addition to raising the £1 million needed to support its Heritage Lottery Fund bid, the Trust also needs short-term assistance in the region of £250,000 per year to support its operational costs."

Dr Black echoes the strong feeling of determination shared by all of its supporters: "If there were an serious outbreak of swine flu, for example, and visitor numbers dropped, Bletchley Park in its current financial state would have to close. We cannot allow that to happen."

Once the ambitious plans for the museum redevelopment have been realized, it is hoped that this important site - much of its history still shrouded in secrecy - will be self-supporting and secure.

If you would like more information on Bletchley Park, discover more about its history, find out what's going on or want to get involved in the campaign to help secure its long-term future, visit the website for more information.

Image credits: Bletchley Park Trust (BP), John Harper (JH) and Creative Commons (CC).

A short documentary video outlining the important role of the women of Station X: