CHAPTER 11

Breaking machines

with a pencil

m av i s b at e y *

D

illy 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.

Introduction

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 focus-

ing mainly on naval and diplomatic messages. When France and Germany also set up cryp-

tographic 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 engi-

neering at Cambridge University, Ewing’s own college, King’s, became a happy hunting ground

*This chapter was revised by Jack Copeland and Ralph Erskine after Mavis Batey’s death in November 2013.