Introduction

Abstract

The story of the Enigma cipher machine and its defeat by the Bletchley Park codebreakers astounded the world. This book describes Bletchley’s success against a later and more advanced German cipher machine that the British codenamed Tunny (see photograph 28). How Bletchley Park broke Tunny has been a closely guarded secret since the end of the war. Unlike Enigma, which dated from 1923 and was marketed openly throughout Europe, the ultra-secret Tunny was created by scientists of Hitler’s Third Reich for use by the German Wehrmacht. Tunny was technologically more sophisticated than Enigma and—theoretically—more secure. From 1942 Hitler and the German High Command in Berlin relied increasingly on Tunny to protect their communications with Army Group commanders across Europe. The Tunny network carried the highest grade of intelligence. Tunny messages sent by radio were first intercepted by the British in June 1941. After a year-long struggle with the new cipher, Bletchley Park had its first successes against Tunny in 1942. Broken Tunny messages contained intelligence that changed the course of the war, saving an incalculable number of lives. Central to the Bletchley attack on Tunny was Colossus, the world’s first large-scale electronic digital computer. The first Colossus was built during 1943 by Thomas H. Flowers and his team of engineers and wiremen, a tight-knit group who worked in utmost secrecy and at terrific speed. The construction of the machine took them ten months, working day and night, pushing themselves until (as Flowers said) their ‘eyes dropped out’. The racks of complex electronic equipment were transferred from Flowers’ laboratory at Dollis Hill in London to Bletchley Park, where Colossus was reassembled. Despite the fact that no such machine had previously been attempted, the computer was in working order almost straight away and ready to begin its fast-paced attack on the German messages. The name ‘Colossus’ was certainly apt. Colossus was the size of a room and weighed approximately a ton. By the end of the war in Europe there were ten Colossi. The computers were housed in two vast steel-framed buildings—a factory dedicated to breaking Tunny. There are photographs of some of the Colossi in the centre of the book.