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tragic irony that the British security services should have been mobilized to exclude Turing—
whose contribution to the work of GCHQ was of such inestimable value during the war—yet
failed so conspicuously to detect the activities of the mole Geoffrey Prime, later convicted of
spying for the Soviet Union while he was working at GCHQ. I. J. Good, a wartime colleague
and friend, has so aptly remarked about Turing’s tremendous contributions to the Nazi defeat:^2
Fortunately, the authorities did not know Turing was a homosexual. Otherwise we might have
lost the war.
Great orginality
If I were to attempt to characterize the nature of Turing’s genius, I would say that it lay in his
capacity for thought of great originality, so often going back to first principles for his inspira-
tion. Even the most superficial examination of his œuvre shows how often he took up a new
topic. His publications range very widely indeed; but to certain topics, in which he made fun-
damental advances, he made only one or two published contributions.
His very characteristic way of thinking can be illustrated by relating certain more light-
hearted episodes in Turing’s life, which also point up his quirky and infectious sense of humour.
Let me describe first his approach to the game of tennis. Turing was a superb athlete—indeed, a
marathon runner of great distinction. At Bletchley Park, he developed a real delight in playing
tennis, and especially enjoyed playing doubles. He was very good up at the net, where his speed
and good eye enabled him to make many effective interceptions. However, he was dissatisfied
with his success rate—too often he intercepted a return from an opponent, but sent the ball
into the net. Applying his remarkable thinking processes to a mundane problem, he reasoned
as follows:
The problem is that, when intercepting, one has very little time to plan one’s stroke. The time
available is a function of the tautness of the strings of my racquet. Therefore I must loosen the
strings.
Being Alan Turing, he then carried out the necessary alterations to his racquet himself. At
this point, my recollection may be coloured by the great distance in time, but I seem to recall
Turing turning up for his next game with a racquet somewhat resembling a fishing net. He was
absolutely devastating, catching the ball in his racquet and delivering it wherever he chose—but
plainly in two distinct operations and, therefore, illegally. He was soon persuaded to revert to a
more orthodox racquet.
When the danger of an invasion of the UK by German paratroops seemed a really serious
one, Turing volunteered for the Local Defence Volunteers, popularly known as the Home
Guard, in order to become an expert at firing a rifle and hitting his target. In order to be
enrolled it was, of course, necessary to complete a massive form full of irrelevant questions.
As all those experienced in government bureaucracy know, when completing such forms the
only essentials are to give one’s name, to sign and date the form, and to answer every question.
The answers themselves don’t matter, because they are never likely to be read. One of the
questions was:
Do you understand that, by enrolling in His Majesty’s Local Defence Volunteers, you render
yourself liable for military discipline?