In the early days the successful cracking of a code relied to a certain extent on insights and inspired guesses by the cryptologists as to the likely behaviour of the German operatives of the machines. Some frequently used insights were named after the person who first proposed them e.g. the Herivel tip, or Herivelismus, after John Herivel and Parkerismus after Reg Parker.
Outstanding work by the GC&CS cryptanalysts enabled some messages to be broken as early as 1940. Further clues as to the workings of the Enigma machines and of the naval codes used were obtained by the capture of German weather boats off Iceland in 1940–41; however, as code settings were changed each month they could be broken only for a limited period. Then, in May 1941, U-boat U-110 attacked a convoy though depth charges fired by the escorting vessels forced her to surface, whereupon her crew abandoned ship. Instead of ramming and sinking her, the captain of HMS Bulldog ordered one of his officers, Sub-Lieutenant David Balme RN, to be rowed over, board the submarine, and retrieve anything of interest. Among the prize items of equipment he took back to Bulldog were an Enigma machine and current code books, which were then rushed to Bletchley Park in great secrecy. (Balme was awarded the DSC.) Next, in October 1942, U-559 was sunk in the eastern Mediterranean. Before she went under, three crew members of the attacking ship, HMS Petard, were able to board her and recover the code books. Sadly, the submarine sank suddenly, taking two of the boarding party with her.
Lorenz and Tunny
In mid-1941 the Germans started using the more sophisticated Lorenz cypher machines; some 12 months later, the German High Command began to use the system for its high-level communications with its Army Commands. The Lorenz signal traffic was known as Tunny by the Bletchley Park cryptanalysts. As the result of an error by a German transmitter in late August 1941, by January 1942 John Tiltman and Bill Tutte had worked out the complete logical structure of the cypher machine, thereby enabling Tunny to be decoded. This remarkable piece of reverse engineering was later described as ‘one of the greatest intellectual feats of World War 2’.
Tiltman, John Hessell Brigadier CMG CBE MC (1894–1982)
A British Army officer, he moved to intelligence work after being wounded during the First World War, initially working with the Indian Army and then at the Government Code and Cypher School (GC&CS). His intelligence work was largely connected with cryptography, and he showed exceptional skill at cryptanalysis. He was considered one of Bletchley Park’s finest cryptanalysts on non-machine systems and worked with Bill Tutte on the cryptanalysis of the Lorenz cypher. In 1944, he was appointed deputy director of GC&CS and continued there until 1949 when he moved to the US Army Security Agency as a liaison officer. He eventually became a consultant and researcher at the US National Security Agency. In September 2004, he was inducted into the ‘NSA Hall of Honor’, the first non-US citizen to be recognised in that way. The NSA commented:‘His efforts at training and his attention to all the many facets that make up cryptology inspired the best in all who encountered him.’
Tutte, William (Bill) Thomas OC FRS FRSC (1917–2002)
The son of a gardener, he became a British, and later a Canadian, mathematicianand code-breaker. Having graduated with a degree in chemistry from Trinity College, Cambridge, he worked at Bletchley Park, initially on Italian Navy codes but from mid-1941 on Tunny, the signal traffic generated by the Lorenz coding machine. His brilliant and fundamental deciphering work led to the code being broken and, eventually, to the creation of the Colossus computing machine. Post-war he emigrated to Canada where he held senior positions at the universities of Toronto and Waterloo. He had a number of significant mathematical accomplishments, including foundational work in the fields of graph and matroid theories.
Turing, Alan (1912–54)
A mathematician and computer scientist, Turing was appointed a fellow of King’s College, Cambridge, in 1935 at the early age of 23. At the outbreak of war he was recruited to the Government’s code-breaking staff at Bletchley Park where he was instrumental in breaking the German naval codes. With Gordon Welchman he designed the Bombe decoding machine and then with Tommy Flowers he designed and developed 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)
