Tens of thousands of people have worked in Sigint over the years – many of them people with unique skills and extraordinary ingenuity who have made a huge difference to the defence of this nation and its interests. A very few of them are described here.
A lecturer at the Naval College at Osborne in 1914, A G Denniston was a member of Room 40 from its beginning during World War 1. He became the first head of GC&CS in 1919 and led the organisation during the inter-War years. It was his foresight which led to the recruitment of new blood – including Alan Turing - for the organisation in 1938. He oversaw the move from London to Bletchley Park in 1939 and led the establishment of closer liaison with US SIGINT experts. He was unceremoniously moved sideways in 1942 and retired in 1945.
Alfred Dillwyn 'Dilly' Knox
A Greek scholar, Dilly Knox was another of the original members of Room 40. He perhaps best exemplifies the mindset of the great cryptanalysts. In 1937, he became the first British cryptanalyst to decrypt operational Enigma traffic being used in Spain and it was he who mentored Alan Turing when the latter came to Bletchley Park.
Nigel de Grey
In 1917, Nigel de Grey, also Room 40 cryptanalyst, played the key role in decrypting the Zimmermann Telegram and recognising it as potentially the key to bringing the USA into the war on the Allied side. He left Room 40 at the end of the war, but came back into Sigint in 1939, being mainly responsible for intelligence production, and remained until he retired in 1947 (although he spent a year between 1950-51 working in the Historical Section).
Brigadier John Tiltman MC
John Tiltman was first attached to GC&CS in 1920. He founded the Military Section and remained its Head throughout WWII. Between the wars, he is best remembered for MASK, the work he led against the Comintern. He was responsible for the first British success against the main Japanese naval code, JN25, shortly after it was introduced in June 1939. And in 1941 he deciphered the message which led eventually to the solution of the German High Command's teleprinter system 'Tunny'. He played a crucial part in developing relationships with US Sigint authorities and after eventually retiring from GCHQ, he went to work at NSA where he remained until he was 80.
Posthumously, the most famous alumnus of Bletchley Park, Alan Turing was recruited in 1938 and after taking part in some specially devised courses, joined Bletchley Park in September 1939. He worked with Dilly Knox on Enigma and met Polish counterparts in Paris early in 1940. He designed the Bombe, the first special-purpose cryptanalytic machine, and made major contributions to the exploitation of German Naval Enigma, before moving on to work on secure speech systems. After the war, working at Manchester University, he and Max Newman, another BP mathematician, led a team that produced Britain's first general purpose stored programme computer (the Ferranti Mk 1).
Tommy Flowers, an employee of the GPO's Research Section conceived COLOSSUS, the first large-scale electronic machine and the forerunner of the modern computer, and led the team which built it. COLOSSUS was used against the German enciphered teleprinter system. Eventually ten COLOSSUS machines were built, and their output provided vital intelligence for the Military, particularly before D Day
James Ellis, a mathematician and computer scientist, joined GCHQ in 1952, having previously worked for the Admiralty. He worked on a number of important cryptographic developments but his identification of the concept of Public Key Cryptography (PKC) was the most significant and far-reaching. This discovery remained classified for a long time and was, at first, only made available for official governmental communications. However, PKC was later thought of independently and developed commercially, and is now the basis for all secure transactions on the Internet.