Denniston's support for a culture of individualism and ingenuity
By late 1939, GC&CS was using Government Communications Headquarters, GCHQ, as a covername (and which would become its official title in 1946). The organisation was in a state of continuous expansion for the next few years, and by the time of the Battle of Britain was beginning to make serious breakthroughs into the crypt systems being used by enemy forces. The intelligence these breakthroughs produced bought 'C' access to the Prime Minister in a way that intelligence never had previously, and the pressure to maintain production became intense.
These breakthroughs had come about because Denniston had persuaded the Treasury to let him recruit new staff even though at first he had little relevant intelligence to show from this expansion. He fostered what would now be called a culture of innovation, allowing new and existing members of staff to contribute in ways not previously considered: Turing, leading work on electromechanical support to decryption, is probably best known, but Gordon Welchman's contribution, not least in understanding and planning for the industrialisation of Sigint, was equally important.
In the 2014 film The Imitation Game, Denniston is portrayed as a coarse jingoistic martinet, bullying and threatening Turing for the failure of his machine to produce results. While the filmmakers no doubt wanted to contrast the tragic solitary genius stereotype they had created for Turing, with an ignorant red-faced military stereotype, Denniston's role couldn't have been more inaccurately written. It was Denniston who interviewed and selected Turing in the autumn of 1938; Denniston who oversaw the two training courses Turing and others attended in January and March 1939; Denniston who approved allowing Turing to take details of Naval Enigma back to Cambridge to work on in the spring and summer of 1939; and Denniston who allowed Turing to visit Paris in January 1940 to discuss Enigma with Marian Rejewski and the other Polish mathematicians-turned-cryptanalysts who had escaped to France.
While the filmmakers were simply trying to tell a good story, they also misrepresented one of the cultural innovations Denniston cherished. He had realised by 1938 that he needed a new sort of person in the organisation: someone who would be as comfortable with technology as their targets in the German military were. He did not just want or need engineers, he needed geniuses who could conceptualise and implement new methods of producing intelligence. Denniston valued who his staff were, how they thought, and how together they developed ideas and concepts. Throughout his time at the head of GC&CS he sought to create an environment in which the disparate talents of individuals, no matter how idiosyncratic, could be harnessed to a common end.