Breaking machines with a pencil

Dilly Knox, the renowned First World War codebreaker, was the first to investigate the workings of the Enigma machine after it came on the market in 1925, and he developed hand methods for breaking Enigma. What he called ‘serendipity’ was truly a mixture of careful observation and inspired guesswork. This chapter describes the importance of the pre-war introduction to Enigma that Turing received from Knox. Turing worked with Knox during the pre-war months, and when war was declared he joined Knox’s Enigma Research Section at Bletchley Park. Once a stately home, Bletchley Park had become the war station of the Secret Intelligence Service (SIS), of which the Government Code and Cypher School (GC&CS) was part. Its head, Admiral Sir Hugh Sinclair, was responsible for both espionage (Humint) and the new signals intelligence (Sigint), but the latter soon became his priority. Winston Churchill was the first minister to realize the intelligence potential of breaking the enemy’s codes, and in November 1914 he had set up ‘Room 40’ right beside his Admiralty premises. By Bletchley Park’s standards, Room 40 was a small-scale codebreaking unit focusing mainly on naval and diplomatic messages. When France and Germany also set up cryptographic bureaux they staffed them with servicemen, but Churchill insisted on recruiting scholars with minds of their own—the so-called ‘professor types’. It was an excellent decision. Under the influence of Sir Alfred Ewing, an expert in wireless telegraphy and professor of engineering at Cambridge University, Ewing’s own college, King’s, became a happy hunting ground for ‘professor types’ during both world wars—including Dillwyn (Dilly) Knox (Fig. 11.1) in the first and Alan Turing in the second. Until the time of Turing’s arrival, mostly classicists and linguists were recruited. Knox himself had an international reputation for unravelling charred fragments of Greek papyri. Shortly after Enigma first came on the market in 1925, offering security to banks and businesses for their telegrams and cables, the GC&CS obtained two of the new machines, and some time later Knox studied one of these closely.