What is Ultra?
[[File:EnigmaMachine Warzawa.jpg|thumb|250px | [[Enigma machine]] out of its wooden box ]] [[File:Lorenz-SZ42-2.jpg|thumb|250px| [[Lorenz cipher|Lorenz SZ42 machine]] with covers removed ]] [[File:Purple code machine 2.jpg|thumb|250px| Part of Japanese [[Purple (cipher machine)|PURPLE machine]] with covers removed]] '''Ultra''' was the name given by [[United Kingdom|British]] [[military intelligence]] for the attack on [[Third Reich|German]] military [[codes]] in [[World War II]]. It included the [[Enigma machine]] and, later, the Japanese [[Purple machine]]. The work on Enigma started before the war, when [[Poles|Polish]] [[cryptography|cryptographers]] smuggled out an Enigma machine to England. The codename 'Ultra', however, was only given to the work in 1941. Work on understanding the Enigma, and on breaking German military signals, was of vital importance in the [[Battle of the Atlantic]], the greatest [[threat]] to Britain during the war.<ref>Hough R. 1986. ''The longest battle: the war at sea 1939-45''. London: Weidenfeld & Nicolson.</ref> The key event occurred in 1941, when not just a machine, but also a codebook, was got from a German [[submarine]].<ref>Kahn D. ''Seizing the Enigma: the race to break the German U-Boat codes, 1939{{ndash}}1943''. London: Souvenir Press 1992.</ref> Wartime [[signals intelligence]] (SIGINT) were got as follows. First of all, [[encryption|encrypted]] German radio messages in [[Morse code]] were recorded in Britain. Their place of origin was got by recording the messages at two different receiving places. The attack on the codes was done at the [[Government Communications Headquarters#Government Code and Cypher School (GC&CS)|Government Code and Cypher School (GC&CS)]] at [[Bletchley Park]].<ref>Hinsley F.H. & Stripp, Alan (eds) 1992. ''Codebreakers: The inside story of Bletchley Park''. Oxford: Oxford University Press. {{ISBN|978-0-19-280132-6}}</ref><ref>Smith M. 1998. ''Station X: the codebreakers of Bletchley Park''. London: Channel 4 books.</ref><ref>Welchman G. 19