Editing Cryptanalysis of the Enigma (section)

===American ''bombes''===
{{Further-text|[[Bombe#US Navy Bombe|US Navy Bombe]] and [[Bombe#US Army Bombe|US Army Bombe]]}}
Unlike the situation at Bletchley Park, the United States armed services did not share a combined cryptanalytical service. Before the US joined the war, there was collaboration with Britain, albeit with a considerable amount of caution on Britain's side because of the extreme importance of Germany and her allies not learning that its codes were being broken. Despite some worthwhile collaboration among the cryptanalysts, their superiors took some time to achieve a trusting relationship in which both British and American bombes were used to mutual benefit.

In February 1941, Captain [[Abraham Sinkov]] and Lieutenant [[Leo Rosen]] of the US Army, and Lieutenants Robert Weeks and [[Prescott Currier]] of the US Navy, arrived at Bletchley Park, bringing, among other things, a replica of the [[Type B Cipher Machine|"Purple" cipher machine]] for Bletchley Park's Japanese section in [[Hut 7]].<ref>{{Harvnb|Budiansky|2000|p=176}}</ref> The four returned to America after ten weeks, with a naval radio direction-finding unit and many documents,<ref>{{Harvnb|Budiansky|2000|p=179}}</ref> including a "paper Enigma".<ref>{{Harvnb|Jacobsen|2000}}</ref>

The main American response to the 4-rotor Enigma was the US Navy bombe, which was manufactured in much less constrained facilities than were available in wartime Britain. Colonel [[John Tiltman]], who later became Deputy Director at Bletchley Park, visited the US Navy cryptanalysis office (OP-20-G) in April 1942 and recognised America's vital interest in deciphering U-boat traffic. The urgent need, doubts about the British engineering workload, and slow progress prompted the US to start investigating designs for a Navy bombe, based on the full [[blueprint]]s and wiring diagrams received by US Navy Lieutenants Robert Ely and Joseph Eachus at Bletchley Park in July 1942.<ref>{{Harvnb|Budiansky|2000|p=238}}</ref><ref>{{Harvnb|Wilcox|2001|p=21}}</ref> Funding for a full, $2 million, Navy development effort was requested on 3 September 1942 and approved the following day.

[[File:US-bombe.jpg|thumb|US Navy bombe. It contained 16 four-rotor Enigma-equivalents and was much faster than the British bombe.]]
Commander Edward Travis, Deputy Director and [[Francis Birch (cryptographer)|Frank Birch]], Head of the German Naval Section travelled from Bletchley Park to Washington in September 1942. With [[Carl Frederick Holden]], US Director of Naval Communications they established, on 2 October 1942, a UK:US accord which may have "a stronger claim than [[1943 BRUSA Agreement|BRUSA]] to being the forerunner of the [[UK–USA Security Agreement|UKUSA Agreement]]", being the first agreement "to establish the special [[signals intelligence|Sigint]] relationship between the two countries", and "it set the pattern for UKUSA, in that the United States was very much the senior partner in the alliance".<ref>{{Harvnb|Erskine|1999|pp=187–197}}</ref> It established a relationship of "full collaboration" between Bletchley Park and OP-20-G.<ref>{{Harvnb|Budiansky|2000|p=239}}</ref>

An all electronic solution to the problem of a fast bombe was considered,<ref>{{Harvnb|Budiansky|2000|p=241}}</ref> but rejected for pragmatic reasons, and a contract was let with the [[NCR Corporation|National Cash Register Corporation]] (NCR) in [[Dayton, Ohio]]. This established the [[United States Naval Computing Machine Laboratory]]. Engineering development was led by NCR's [[Joseph Desch]], a brilliant inventor and engineer. He had already been working on electronic counting devices.<ref>{{citation |last=Desch |first=Joseph R. |author-link=Joseph Desch |title=1942 Research Report |date=21 January 1942 |url=https://www.daytoncodebreakers.org/wp-content/uploads/42rep.pdf |access-date=20 July 2013}}</ref>

Alan Turing, who had written a memorandum to OP-20-G (probably in 1941),<ref>{{Harvnb|Turing|c. 1941|pp=341–352}}</ref> was seconded to the British Joint Staff Mission in Washington in December 1942, because of his exceptionally wide knowledge about the bombes and the methods of their use. He was asked to look at the bombes that were being built by NCR and at the security of certain speech cipher equipment under development at Bell Labs.<ref>{{citation |title=Bletchley Park Text: November 1942: Departure of Alan Turing from BP |url=http://cipherweb.open.ac.uk/cgi-bin/cipher-demo/mobile/sms_categories_xml.py? |access-date=16 April 2010}}{{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes}}</ref> He visited OP-20-G, and went to NCR in Dayton on 21 December. He was able to show that it was not necessary to build 336 Bombes, one for each possible rotor order, by utilising techniques such as [[Banburismus]].<ref>{{Harvnb|Budiansky|2000|p=242}}</ref> The initial order was scaled down to 96 machines.

The US Navy bombes used drums for the Enigma rotors in much the same way as the British bombes, but were very much faster. The first machine was completed and tested on 3 May 1943. Soon these bombes were more available than the British bombes at Bletchley Park and its outstations, and as a consequence they were put to use for Hut 6 as well as Hut 8 work.<ref name="Welchman97p135" >{{Harvnb|Welchman|1997|p=135}}</ref> A total of 121 Navy bombes were produced.<ref name=WengerWilcoxP52/>

The US Army also produced a version of a bombe. It was physically very different from the British and US Navy bombes. A contract was signed with [[Bell Labs]] on 30 September 1942.<ref>{{Harvnb|Sebag-Montefiore|2004|p=254}}</ref> The machine was designed to analyse 3-rotor, not 4-rotor traffic. It did not use drums to represent the Enigma rotors, using instead telephone-type relays. It could, however, handle one problem that the bombes with drums could not.<ref name="Welchman97p135"/><ref name=WengerWilcoxP52/> The set of ten bombes consisted of a total of 144 Enigma-equivalents, each mounted on a rack approximately {{convert|7|ft|m}} long {{convert|8|ft|m}} high and {{convert|6|in|mm}} wide. There were 12 control stations which could allocate any of the Enigma-equivalents into the desired configuration by means of plugboards. Rotor order changes did not require the mechanical process of changing drums, but was achieved in about half a minute by means of push buttons.<ref name=WengerWilcoxP51 >{{Harvnb|Wenger|1945|p=51}}</ref> A 3-rotor run took about 10 minutes.<ref name=WengerWilcoxP52 >{{Harvnb|Wenger|1945|p=52}}</ref>