Free The Bletchley Park Codebreakers by Michael Smith

war ‘was won, in a very large measure, as a result of the availability of American communication receivers’.
    Breaking Enigma is sometimes thought to have been a task carried out by a few cryptanalysts, working on their own in back rooms. In fact, most of the work was done by relatively unskilled staff, and the cryptanalysts were very much in a minority - and seldom eccentric. There was so much traffic that Hut 6 had to adopt production-line methods to deal with it. Running Hut 6 as a well-organized and flexible unit, while maintaining staff morale at a high level, required considerable leadership and management skills, especially since many staff were doing boring and monotonous work under difficult conditions. Fortunately, Gordon Welchman, the first head of Hut 6, and his successor, Stuart Milner-Barry, rose to the challenge well. Not every unit at Bletchley was so well managed.
    It is sometimes claimed that Hut 6 was completely on top of Enigma by the end of 1944, and that it was often quickly and easily broken then. Chapter 4 shows that nothing could be further from the truth. In November 1944, when Hut 6 was attacking about sixty-five
Heer
and
Luftwaffe
Enigma ciphers, Hut 6’s demands for bombe time became prodigious, and it required considerable help from US Navy bombes in Washington. The US Navy had generously agreed in November 1943 to handle Hut 6 ciphers on its bombes on exactly the same basis as
Kriegsmarine
(German Navy) ciphers, except for the main naval cipher. Shark: it kept to that decision for the rest of the war, despite being worried about impinging on the functions of the US Army codebreakers, which was always a highly sensitive issue.
    Chapter 4 describes the methods used by Hut 6 to penetrate
Heer
and
Luftwaffe
Enigma, and shows the many difficulties that they faced, especially with
Heer
ciphers. It was a close-run thing, especially in late 1944 and 1945, when Milner-Barry thought that Hut 6 was on the verge of losing its hold on Enigma.
    RE
    The Polish Cipher Bureau,
Bureau Szyfrow
(BS), had attacked German codes successfully in the 1920s until 1926, when the German Navy adopted two simple versions of Enigma. In 1928, the Bureau became blind against much of the German Army traffic, which had also started to use Enigma. The Cipher Bureau realized that a machine cipher required special talents to solve it, and in 1929 gave selected mathematics students a course in cryptology. The only three to complete the course, Jerzy Różycki, Henryk Zygalski and Marian Rejewski, were recruited by the Bureau, although initially they worked only on a part-time basis.
    The German Army added a plugboard to Enigma in 1930, but it was not until September 1932 that Rejewski, who was the star among the young cryptanalysts, was given the plugboard Enigma to attack on his own – the older cryptanalysts in the Bureau had been trying to solve it since its introduction, but had completely failed. By the end of that year, Rejewski had reconstructed the wiring of Enigma’s rotors mathematically, using permutation theory, in an outstanding feat of cryptanalysis. The fatal flaw in Enigma had been its indicating system, which used doubly enciphered message keys (see Appendix II). Rejewski described the system as ‘the third secret’ of military Enigma, although he also received invaluable help from Enigma key-lists which had been received from Gustave Bertrand, in French military intelligence: Bertrand had bought them from Hans-Thilo Schmidt, who was working in the German Defence Ministry’s
Chiffrierstelle
(Cipher Centre). The indicating system was also exploited by the Poles to solve Enigma traffic in 1938 and 1939 using electro-mechanical machinery known as
bombas
(bombes), and a system of perforated sheets invented by Zygalski. Rejewski also reconstructed the wiring of rotors IV and V when they were introduced in December 1938.
    Plugboard Enigma, which was the only type used by the
Wehrmacht
during the war, measured