Tommy Flowers
Thomas Flowers, the son of John Thomas Flowers, bricklayer, and his wife, Mabel Richardson Flowers, was born at 160 Abbott Road, Poplar, London, on 22nd December, 1905. He always loved making things and when his sister was born in 1910, he "complained at the time that he would have preferred a Meccano set". (1)
Flowers gained a scholarship that enabled him to attend technical college until he was sixteen. in 1921 he started a four-year mechanical apprenticeship at the Royal Arsenal in Woolwich, while at the same time he attended evening classes, gaining a London University degree in engineering.
In 1926 Flowers joined the Post Office as an electrical engineer, and in 1930 he moved to the Post Office Research Station at Dollis Hill. The station was dedicated mainly to research in telecommunications and was responsible for the development of the Trans-Atlantic telephone cable. As Alan Hodges has pointed out: "His major research interest over the years had been long distance signalling, and in particular the problem of transmitting control signals, so enabling human operators to be replaced by automatic switching equipment. Even at this early date he had considerable experience of electronics, having started research on the use of electronic valves for telephone switching in 1931. This work had resulted in an experimental toll dialling circuit which was certainly operational in 1935." (2)
On 31st August 1935 Flowers married Eileen Green. Over the next few years the couple had two sons, Kenneth and John. In the late 1930s Tommy Flowers built up considerable experience and expertise in the use of valves, in particular developing systems of valve amplifiers and switches that by 1939 enabled long-distance calls to be made without the intervention of an operator. (3)
Bletchley Park
In February 1941, Gordon Radley, the director of the Post Office Research Station was contacted by officials of Bletchley Park, the government's codebreaking establishment. Alan Turing wanted help in building a decoder for a machine he had designed to decipher messages sent by the German military during the Second World War. Turing was put in contact with Tommy Flowers. Although the decoder project was abandoned, Turing was impressed with Flowers's work, and in February 1943 introduced him to Max Newman, who had been given the problem of dealing with the Lorenz SZ machine that was used to encrypt communications between Adolf Hitler and his generals.
The Lorenz SZ operated in a similar way to the Enigma Machine, but was far more complicated, and it provided the Bletchley codebreakers with an even greater challenge. It used a 32-letter Baudot alphabet. "While Enigma machines were capable of 159 trillion settings, the number of the combinations possible with the Lorenz SZ was estimated at 5,429,503,678,976 times greater." (4)
Newman came up with a way to mechanise the cryptanalysis of the Lorenz cipher and therefore to speed up the search for wheel settings. (5) Flowers later explained the objective of Newman's machine: "The purpose was to find out what the positions of the code wheels were at the beginning of the message and it did that by trying all the possible combinations and there were billions of them. It tried all the combinations, which processing at 5,000 characters a second could be done in about half an hour. So then having found the starting positions of the cipher wheels you could decode the message." (6)
Colossus Mark I
The initial machine designed by Max Newman kept on breaking down. Flowers later recalled: "I was brought in to to make it work, but I very soon came to the conclusion that it would never work. It was dependent on paper tape being driven at very high speed by means of spiked wheels and the paper wouldn't stand up to it." Flowers suggested that Newman used valves instead of the old-fashioned electromechanical relay switches that had been used in Turing's machines. He claimed valves would do the same job much faster without the need for the synchronisation of the two tapes.
Gordon Welchman, a colleague at Bletchley Park, pointed out: "Flowers seems to have realized at once that synchronization 44 punched-tape operations need not depend on the mechanical process of using sprocket holes. He used photoelectric sensing, and at that early date he had enough confidence in the reliability of switching networks based on electronic valves (tubes, in America), rather than electromagnetic relays, to risk using such techniques on a grand scale. From his prewar experience, Flowers knew that most valve failures occurred when, or shortly after, power was switched on, and he designed his equipment with this in mind. He proposed a machine using 1,500 valves." (7)
Tommy Flowers claimed that Newman and his team of codebreakers were highly sceptical of his suggestion: "They wouldn't believe it. They were quite convinced that valves were very unreliable. This was based on their experience of radio equipment which was carted around, dumped around, switched on and off, and generally mishandled. But I'd introduced valves into telephone equipment in large numbers before the war and I knew that if you never moved them and never switched them off they would go on forever. They asked me how long it would take to produce the first machine. I said at least a year and they said that was terrible. They thought in a year the war could be over and Hitler could have won it so they didn't take up my idea." (8)
The project was now shelved. However, Flowers was so convinced that he could get Newman machine to work effectively he continued building the machine. At the Post Office Research Station at Dollis Hill Flowers took Newman's blueprint and spent ten months turning it into the Colossus Computer, which he delivered to Bletchley Park on 8th December 1943, but was not fully operational until 5th February 1944. It consisted of 1,500 electronic valves, which were considerably faster than the relay switches used in Turing's machine. However, as Simon Singh, the author of The Code Book: The Secret History of Codes & Code-Breaking (2000) has pointed out than "more important than Colossus's speed was the fact that it was programmable. It was this fact that made Colossus the precursor to the modern digital computer." (9)
Newman's staff that operated the Colossus consisted of about twenty cryptanalysts, about six engineers, and 273 Women's Royal Naval Service (WRNS). Jack Good was one of the cryptanalysts working under Newman: "The machine was programmed largely by plugboards. It read the tape at 5,000 characters per second... The first Colossus had 1,500 valves, which was probably far more than for any electronic machine previously used for any purpose. This was one reason why many people did not expect Colossus to work. But it began producing results also immediately. Most of the failures of valves were caused by switching the machine on and off." (10)
Harry Fensom later reported: "The Colossi were of course very large, hence their name, and gave off a lot of heat, ducts above them taking some of this away. However, we appreciated this on the cold winter nights, especially about two or three in the morning. When I came in out of the rain, I used to hang my raincoat on the chair in front of the hundreds of valves forming the rotor wheels and it soon dried off. Of course it was essential that the machines were never switched off, both to avoid damaging the valves and to ensure no loss of code-breaking time. So there was an emergency mains supply in the adjoining bay which took over automatically on mains failure." (11)
Colossus Mark II
In February, 1944, the Lorenz SZ40 machine was further modified in an attempt to prevent the British from decyphering it. With the invasion of Europe known to be imminent, it was a crucial period for the codebreakers, as it was vitally important for Berlin to break the code being used between Adolf Hitler in Berlin and Field Marshal Gerd von Rundstedt, the Commander-in-Chief of the German Army in western Europe. (12)
Tommy Flowers and Max Newman now began working on a more advanced computer, Colossus Mark II. Flowers later recalled: "We were told if we couldn't make the machine work by June 1st it would be too late to be of use. So we assumed that that was going to be D-Day, which was supposed to be a secret." The first of these machines went into service at Bletchley Park on 1st June 1944. It had 2,400 valves and could process the tapes five times as fast. "The effective speed of sensing and processing the five-bit characters on punched paper tape was now twenty-five thousand characters per second... Flowers had introduced one of the fundamental principles of the postwar digital computer - use of a clock pulse to synchronize all the operations of his complex machine." (13) It has been pointed out that the speed of the Mark II was "comparable to the first Intel microprocessor chip introduced thirty years later". (14)
When the night staff arrived for work just before midnight on 4th June, 1944 they were informed that tomorrow was D-Day: "They told us that D-Day was today and they wanted every possible message decoded as fast as possible. But then it was postponed because the weather was so bad and that meant we girls knew it was going to take place, so we had to stay there until D-Day. We slept where we could and worked when we could and of course then they set off on June 6, and that was D-Day." (15)
Winston Churchill and his commanders wanted to know if the deception plans for the D-Day landings had been successful. Developed by two agents, Tomás Harris and Juan Pujol: The key aims of the deception were: "(a) To induce the German Command to believe that the main assault and follow up will be in or east of the Pas de Calais area, thereby encouraging the enemy to maintain or increase the strength of his air and ground forces and his fortifications there at the expense of other areas, particularly of the Caen area in Normandy. (b) To keep the enemy in doubt as to the date and time of the actual assault. (c) During and after the main assault, to contain the largest possible German land and air forces in or east of the Pas de Calais for at least fourteen days." (16)
Harris devised a plan of action for Pujol (code name GARBO). He was to inform the Germans that the opening phase of the invasion was under way as the airborne landings started, and four hours before the seaborne landings began. "This, the XX-Committee reasoned, would be too later for the Germans to do anything to do anything to frustrate the attack, but would confirm that GARBO remained alert, active, and well-placed to obtain critically important intelligence." (17)
Christopher Andrew has explained how the strategy worked: "During the first six months of 1944, working with Tomás Harris, he (GARBO) sent more than 500 messages to the Abwehr station in Madrid, which as German intercepts revealed, passed them to Berlin, many marked 'Urgent'... The final act in the pre-D-Day deception was entrusted, appropriately, to its greatest practitioners, GARBO and Tomás Harris. After several weeks of pressure, Harris finally gained permission for GARBO to be allowed to radio a warning that Allied forces were heading towards the Normandy beaches just too late for the Germans to benefit from it." (18)
Tommy Flowers had a meeting with General Dwight D. Eisenhower on 5th June. He was able to tell Eisenhower that Adolf Hitler was not sending any extra troops to Normandy and still believed that the Allied troops would land east of the Pas de Calais. Flowers was also able to report that Colossus Mark II had decoded message from Field Marshal Erwin Rommel that one of the drop sites for an US parachute division was the base for a German tank division. As a result of this information the drop site was changed.
Jean Thompson later explained her role in the operation in the book, Station X: The Codebreakers of Bletchley Park (1998): "Most of the time I was doing wheel setting, getting the starting positions of the wheels. There would be two Wrens on the machine and a duty officer, one of the cryptanalysts - the brains people, and the message came in on a teleprinted tape. If the pattern of the wheels was already known you put that up at the back of the machine on a pinboard. The pins were bronze, brass or copper with two feet and there were double holes the whole way down the board for cross or dot impulses to put up the wheel pattern. Then you put the tape on round the wheels with a join in it so it formed a complete circle. You put it behind the gate of the photo-electric cell which you shut on it and, according to the length of the tape, you used so many wheels and there was one moveable one so that could get it taut. At the front there were switches and plugs. After you'd set the thing you could do a letter count with the switches. You would make the runs for the different wheels to get the scores out which would print out on the electromatic typewriter. We were looking for a score above the random and one that was sufficiently good, you'd hope was the correct setting. When it got tricky, the duty officer would suggest different runs to do." (19)
Tommy Flowers 1945-1998
At the end of the war Winston Churchill issued orders that the ten Colossus computers were destroyed and broken into "pieces no bigger than a man's hand". Harry Fensom was one of those who was involved in breaking-up the computers. "I believe some panels went with Max Newman to Manchester University." Jerry Roberts later recalled: "The Colossus machines were all destroyed, except two which got away. There were ten machines - eight were dismantled and destroyed, and two were kept at Cheltenham at the new GCHQ." Tommy Flowers was ordered to destroy all documentation and burnt them in a furnace at Dollis Hill. He later said of that order: "That was a terrible mistake. I was instructed to destroy all the records, which I did. I took all the drawings and the plans and all the information about Colossus on paper and put it in the boiler fire. And saw it burn." (20)
Tommy Flowers returned to Dollis Hill where he became head of the section developing electronic switching, forerunner of the subscriber trunk dialling (STD) system introduced in the post-war decades. He also assisted the National Physical Laboratory's project to build the ACE, an early stored-program computer. As Post Office chief engineer Flowers designed an electronic random-number generator, ERNIE, operational from 1957, to pick winners among holders of premium bonds. (21)
Frederick Winterbotham approached the government and asked for permission to reveal the secrets of the work done at Bletchley Park. The intelligence services reluctantly agreed and Winterbotham's book, The Ultra Secret, was published in 1974. Those who had contributed so much to the war effort could now receive the recognition they deserved. (22) Unfortunately, some of the key figures such as Alan Turing, Alastair Denniston and Alfred Dilwyn Knox were now dead.
In 1977 Flowers's role was recognized, after groundbreaking historical research by the computer scientist Brian Randell, and he was awarded an honorary degree by Newcastle University. He was the first recipient of the Post Office's Martlesham medal, in 1980.
Tommy Flowers died at his home, 8 Holland Court, Page Street, Mill Hill, London, on 28th October 1998.
Primary Sources
(1) Alan Hodges, Alan Turing: the Enigma (1983) page 285
Tommy Flowers... joined the Research Station as a probationary engineer in 1930, after serving his apprenticeship at Woolwich Arsenal. His major research interest over the years had been long distance signalling, and in particular the problem of transmitting control signals, so enabling human operators to be replaced by automatic switching equipment. Even at this early date he had considerable experience of electronics, having started research on the use of electronic valves for telephone switching in 1931. This work had resulted in an experimental toll dialling circuit which was certainly operational in 1935.
(2) Tommy Flowers, quoted by Michael Paterson, the author of Voices of the Codebreakers (2007)
The purpose was to find out what the positions of the code wheels were at the beginning of the message and it did that by trying all the possible combinations and there were billions of them. It tried all the combinations, which processing at 5,000 characters a second could be done in about half an hour. So then having found the starting positions of the cipher wheels you could decode the message.
(3) Gordon Welchman, The Hut Six (1982)
Flowers seems to have realized at once that synchronization 44 punched-tape operations need not depend on the mechanical process of using sprocket holes. He used photoelectric sensing, and at that early date he had enough confidence in the reliability of switching networks based on electronic valves (tubes, in America), rather than electromagnetic relays, to risk using such techniques on a grand scale. From his prewar experience, Flowers knew that most valve failures occurred when, or shortly after, power was switched on, and he designed his equipment with this in mind. He proposed a machine using 1,500 valves, nearly twice the number used in the pioneering ACE computer built in England after the war...
Flowers and his group built the first Colossus in eleven months. Its photoelectric punched-tape reader operated at five thousand characters per second, a remarkable speed for those days. Flowers was a pioneer in the redesign of the electronic decision-making circuits that had been invented before the war. The first "string and sealing wax" (Flowers' own description) version of the Colossus was a tremendous success. Again Flowers and Radley anticipated a future demand and made preliminary arrangements for production. Around March 1944 Dollis Hill received an urgent request from Bletchley Park for more Colossi. They produced them, thanks to their preliminary arrangements, and the effective speed of sensing and processing the five-bit characters on punched paper tape was now twenty-five thousand characters per second. Moreover, as Brian Randell points out, Flowers had introduced one of the fundamental principles of the postwar digital computer-use of a clock pulse to synchronize all the operations of his complex machine.
(4) Tommy Flowers, quoted by Michael Smith, the author of Station X: The Codebreakers of Bletchley Park (1998)
They wouldn't believe it. They were quite convinced that valves were very unreliable. This was based on their experience of radio equipment which was carted around, dumped around, switched on and off, and generally mishandled. But I'd introduced valves into telephone equipment in large numbers before the war and I knew that if you never moved them and never switched them off they would go on forever.
They asked me how long it would take to produce the first machine. I said at least a year and they said that was terrible. They thought in a year the war could be over and Hitler could have won it so they didn't take up my idea. They decided they would proceed hopefully with the Robinson, which is what they did, and they left the question of whether the valve-based machine would be constructed or not to me.
I was so convinced that Robinson would never work that we developed the new machine on our own at Dollis Hill. We made the first prototype in ten months, working day and night, six-and-a-half days a week, twelve hours a day sometimes. We started with the design of what was to be called Colossus in February 1943 and we had the first prototype machine working at Bletchley Park on 8 December.
The purpose of the Colossus was to find out what the positions of the code wheels were at the beginning of the message and it did that by trying all the possible combinations and there were billions of them. It tried all the combinations, which processing at 5000 characters a second could be done in about half an hour. So then having found the starting positions of the cypher wheels you could decode the message.
When we'd made it for them and they saw it work, they were really astounded. It had about 1500 valves in it, which horrified Bletchley Park. But one of the disadvantages of Robinson was that it didn't always give you the right answer. The answer that they got from the machine was in numbers, a counter counted the number of times that certain letters appeared and the counter was a bit unreliable so they didn't always get the same count.
What they did with Colossus, the first day they got it, was to put a problem on it to which they knew the answer. It took about half an hour to do the run. They let it run for about four hours, repeating the processes every half hour, and to their amazement, it gave the same answer every time. They really were amazed. It was that reliable, extremely reliable.
(5) Simon Singh, The Code Book: The Secret History of Codes & Code-Breaking (2000)
During the Second World War, British codebreakers had the upper hand over German codemakers, mainly because the men and women at Bletchley Park, following the lead of the Poles, developed some of the earliest codebreaking technology. In addition to Turing's bombes, which were used to crack the Enigma cipher, the British also invented another codebreaking device, Colossus, to combat an even stronger form of encryption, namely the German Lorenz cipher. Of the two types of codebreaking machine, it was Colossus that would determine the development of cryptography during the latter half of the twentieth century.
The Lorenz cipher was used to encrypt communications between Hitler and his generals. The encryption was performed by the Lorenz SZ40 machine, which operated in a similar way to the Enigma machine, but the Lorenz was far more complicated, and it provided the Bletchley codebreakers with an even greater challenge. However, two of Bletchley's codebreakers, John Tiltman and Bill Tutte, discovered a weakness in the way that the Lorenz cipher was used, a flaw that Bletchley could exploit and thereby read Hitler's messages.
Breaking the Lorenz cipher required a mixture of searching, matching, statistical analysis and careful judgement, all of which was beyond the technical abilities of the bombes. The bombes were able to carry out a specific task at high speed, but they were not flexible enough to deal with the subtleties of Lorenz. Lorenz-encrypted messages had to be broken by hand, which took weeks of painstaking effort, by which time the messages were largely out of date. Eventually, Max Newman, a Bletchley mathematician, came up with a way to mechanise the cryptanalysis of the Lorenz cipher. Drawing heavily on Alan Turing's concept of the universal machine, Newman designed a machine that was capable of adapting itself to different problems, what we today would call a programmable computer.
Implementing Newman's design was deemed technically impossible, so Bletchley's senior officials shelved the project. Fortunately, Tommy Flowers, an engineer who had taken part in discussions about Newman's design, decided to ignore Bletchley's scepticism, and went ahead with building the machine. At the Post Office's research centre at Dollis Hill, North London, Flowers took Newman's blueprint and spent ten months turning it into the Colossus machine, which he delivered to Bletchley Park on 8 December 1943. It consisted of 1,500 electronic valves, which were considerably faster than the sluggish electromechanical relay switches used in the bombes. But more important than Colossus's speed was the fact that it was programmable. It was this fact that made Colossus the precursor to the modern digital computer.Colossus, as with everything else at Bletchley Park, was destroyed after the war, and those who worked on it were forbidden to talk about it. When Tommy Flowers was ordered to dispose of the Colossus blueprints, he obediently took them down to the boiler room and burnt them. The plans for the world's first computer were lost for ever. This secrecy meant that other scientists gained the credit for the invention of the computer. In 1945, J. Presper Eckert and John W Mauchly of the University of Pennsylvania completed ENIAC (Electronic Numerical Integrator And Calculator), consisting of 18,000 electronic valves, capable of performing 5,000 calculations per second. For decades, ENIAC, not Colossus, was considered the mother of all computers.
Having contributed to the birth of the modern computer, cryptanalysts continued after the war to develop and employ computer technology in order to break all sorts of ciphers. They could now exploit the speed and flexibility of programmable computers to search through all possible keys until the correct one was found. In due course, the cryptographers began to fight back, exploiting the power of computers to create increasingly complex ciphers. In short, the computer played a crucial role in the postwar battle between codemakers and codebreakers.
Using a computer to encipher a message is, to a large extent, very similar to traditional forms of encryption. Indeed, there are only three
(6) Jack Good, quoted by Michael Paterson, the author of Voices of the Codebreakers (2007)
The machine was programmed largely by plugboards. It read the tape at 5,000 characters per second and, at least in Mark II, the circuits were in quintuplicate so that in a sense the reading speed was 25,000 bits per second. This compares well with the speed of thc electronic computers of the early 1950s. The first Colossus had 1,500 valves, which was probably far more than for any electronic machine previously used for any purpose. This was one reason why many people did not expect Colossus to work. But it was installed in December 1943 and began producing results almost immediately. Most of the failures of valves were caused by switching the machine on and off.