Engineering Hitler's Downfall. Gwilym Roberts

Colossus, the world’s first computer. Post-war he was appointed to a chair at the University of Manchester, where he continued his computer developments. Turing was prosecuted for homosexual acts in 1952, when such behaviour was still a crime in the UK. He accepted treatment with oestrogen injections (chemical castration) as an alternative to prison. He committed suicide in 1954 and was granted a posthumous pardon in 2013.

      As laborious manual methods necessarily had to be used, the decrypting process was extremely slow. Turing and Welchman therefore set about developing machines which could undertake the work speedily and accurately. The first was the Turing-Welchman Bombe, of which a number were manufactured in 1941; in case Bletchley Park should be bombed, many were installed at outstations.

      Then came the electronic Colossus computing machine, in whose development and manufacture Thomas Flowers, a Post Office engineer, was very largely responsible. It used some 1,800 thermionic valves – a substantial increase on the previous most complicated electronic device which had only used about 150. Some of the senior Bletchley Park management were unconvinced that Flowers’ idea would work, saying he was ‘squandering good valves’, and his funding was cut off, forcing him to pay for the subsequent work himself. However, the project did work, and the first machine became operational in December 1943, thereby enabling Lorenz messages to be read. By the end of the war there were ten in service; they were the precursors of today’s computers.

      Welchman, Gordon OBE (1906–85)

      A mathematician, code-breaker, and computer scientist; although a graduate of Trinity College, Cambridge, he was appointed a fellow and dean of Sidney Sussex College in 1929. On the outbreak of war he joined the Government’s code-breaking school at Bletchley Park and recruited a number of fellow Cambridge mathematicians to work with him. He first headed the Hut 6 team which was charged with deciphering German Army and Air Force codes. With Turing he went on to develop the Turing-Welchman Bombe that enabled German codes to be broken and from which modern computers developed.

      He emigrated to the USA in 1948, and at MIT taught the first computer course in the United States. He then worked for Remington Rand, Ferranti, and the MITRE Corporation on tactical communications systems for the US military. He became a naturalised American citizen in 1962 and retired in 1971, but was retained as a consultant. His book, The Hut Six Story, was published in 1982. The National Security Agency disapproved of this and he lost his security clearance and, in consequence, his consultancy with MITRE. He was also forbidden from discussing either the book or his wartime work with the media. Welchman died in 1985 and his final conclusions and corrections to the story of wartime code-breaking were published posthumously in 1986 in a paper entitled ‘From Polish Bomba to British Bombe: the birth of Ultra’.

      Wrens operating a Colossus machine. PD National Archives FO850/234

      Flowers, Thomas MBE (1905–98)

      The son of a bricklayer, Flowers served an apprenticeship at the Royal Arsenal, Woolwich. While there he obtained an electrical engineering degree from the University of London. He then joined the Post Office as an electrical engineer at their Dollis Hill research station, where he explored the use of electronics for telephone exchanges. In 1942 he was appointed to work with Alan Turing to build a decoder for the relay-based Bombe machine that Turing had developed to help decrypt Enigma codes. Although the decoder project was abandoned, Turing was impressed with Flowers' work, and in February 1943 they began working on developing an automated decoding system for Lorenz cyphers. After initial work with a machine called Heath Robinson, Flowers proposed an electronic system (called Colossus), which was successful and had a major influence on the war’s proceedings. Post-war he became the Post Office’s chief engineer and also worked with the National Physical Laboratory in computer development. His vital work at Bletchley Park was not fully appreciated until many years after the end of the war.

      The organisational arrangements at Bletchley Park reflected the British approach in successfully harnessing brilliant minds to support the war effort. Turing, Welchman, and their colleagues had the ideas, but they needed sympathetic minders such as Commanders Dennison and Travis, both RN, to make their work effective and to provide the organisational framework. It is doubtful whether anything similar occurred anywhere in Germany during the war.

      Y-Service

      Operating out of some 30 separate stations, personnel from the Royal Signals and other agencies listened into German wireless traffic; later from stations in India and elsewhere in the Far East, they listened into Japanese signals. Many amateur (‘ham’) radio operators supported the work of the ‘Y’ stations, being enrolled as ‘Voluntary Interceptors’. Much of the traffic intercepted by these stations was recorded by hand and sent to Bletchley Park on paper by motorcycle couriers or, subsequently, by teleprinter over Post Office landlines. A large house called Arkley View on the outskirts of Barnet acted as a data collection centre at which traffic was collated and passed to Bletchley Park. It also acted as a ‘Y’ station.

      In addition to wireless interception, specially constructed ‘Y’ stations also undertook High Frequency Direction Finding (HF/DF, known colloquially as ‘Huff Duff’) on enemy wireless transmissions. This became particularly important in the Battle of the Atlantic (1939–1945), where locating the positions of U-boats became a critical issue. Admiral Dönitz told his commanders that they could not be located if they limited their wireless transmissions to under 30 seconds, but skilled HF/DF operators were able to locate the origin of their signals in as little as six seconds.

      The land-based DF stations preferred by the Allies operated on the Adcock antennae system, which consisted of a small central operators’ hut surrounded by four 10-metre-tall aerial poles, usually placed at the four compass points. Aerial feeders ran underground and came up in the centre of the hut; these were connected to a direction-finding goniometer and a wireless receiver that allowed the bearing of the signal source to be measured. In the UK some operators were in underground metal tanks. These stations were usually located in remote places, often in the middle of fields. Traces of Second World War D/F stations can be seen as circles in the fields surrounding the village of Goonhavern in Cornwall.

      Far Eastern Codes

      The Japanese had different coding systems for diplomatic, naval, and army messages. Also, after a message had been decoded, it had to be translated before it could be read by most English-speaking officials. Some signals intercepted by British listening stations were sent to the UK for GC&CS cryptologists to attempt to decipher, and in 1939 John Tiltman managed to decode the then-current Japanese naval code.

      Before Pearl Harbour, American, British, Australian, and Dutch cryptanalysts were listening to and trying to decode Japanese naval and other signals. The British office was originally in Hong Kong but then moved to Singapore; Colombo (in Ceylon, now Sri Lanka); and Mombasa, Kenya. Wireless reception there was particularly poor, and in 1943 it returned to Colombo. Following the Japanese invasion of Malaya, Army and RAF decoders were based in Delhi, India.

      The principal Japanese encoding system for diplomatic messages was called Purple by American cryptanalysts, while their decoding work was known as Magic. American and British officials had managed to decode some signals before Pearl Harbour. Later they were able to decipher most Japanese messages. The Russians also succeeded in breaking into the Purple system in late 1941; the messages revealing that Japan was only going to attack the US and UK territories allowed Joseph Stalin to move considerable forces from the Far East just in time to help stop the final German push to Moscow.

      Covert Communication Centres

      Military establishments and training centres of all kinds were established