Editing Cryptanalysis of the Enigma (section)

===''PC Bruno''===
{{Main|PC Bruno}}
On 5 September 1939 the Cipher Bureau began preparations to evacuate key personnel and equipment from Warsaw. Soon a special evacuation train, the Echelon F, transported them eastward, then south. By the time the Cipher Bureau was ordered to cross the border into allied Romania on 17 September, they had destroyed all sensitive documents and equipment and were down to a single very crowded truck. The vehicle was confiscated at the border by a Romanian officer, who separated the military from the civilian personnel. Taking advantage of the confusion, the three mathematicians ignored the Romanian's instructions. They anticipated that in an internment camp they might be identified by the Romanian security police, in which the German [[Abwehr]] and [[Sicherheitsdienst|SD]] had informers.<ref name="Kozaczuk 1984 70–73, 79">{{harvnb|Kozaczuk|1984|pp=70–73, 79}}</ref>

The mathematicians went to the nearest railroad station, exchanged money, bought tickets, and boarded the first train headed south. After a dozen or so hours, they reached Bucharest, at the other end of Romania. There they went to the British embassy. Told by the British to "come back in a few days", they next tried the French embassy, introducing themselves as "friends of Bolek" (Bertrand's Polish code name) and asking to speak with a French military officer. A French Army colonel telephoned Paris and then issued instructions for the three Poles to be assisted in evacuating to Paris.<ref name="Kozaczuk 1984 70–73, 79"/>

On 20 October 1939, at ''[[PC Bruno]]'' outside Paris, the Polish cryptologists resumed work on German Enigma ciphers, in collaboration with Bletchley Park.<ref>{{Harvnb|Kozaczuk|1984|pp=69–94, 104–11}}</ref>

''PC Bruno'' and Bletchley Park worked together closely, communicating via a [[telegraph]] line secured by the use of Enigma doubles. In January 1940 Alan Turing spent several days at ''PC Bruno'' conferring with his Polish colleagues. He had brought the Poles a full set of Zygalski sheets that had been punched at Bletchley Park by [[John R. F. Jeffreys|John Jeffreys]] using Polish-supplied information, and on 17 January 1940, the Poles made the first break into wartime Enigma traffic—that from 28 October 1939.<ref>{{Harvnb|Kozaczuk|1984|pp=84, 94}} note 8</ref> From that time, until the [[Battle of France|Fall of France]] in June 1940, 17 per cent of the Enigma keys that were found by the allies were solved at ''PC Bruno''.<ref>{{Harvnb|Rejewski|1982|pp=81–82}}</ref>

Just before opening their 10 May 1940 offensive against the Low Countries and France, the Germans made the feared change in the indicator procedure, discontinuing the duplication of the enciphered message key. This meant that the Zygalski sheet method no longer worked.<ref name="Rejewski84P243">{{Harvnb|Rejewski|1984c|p=243}}</ref><ref>{{Harvnb|Rejewski|1984d|pp=269–70}}</ref> Instead, the cryptanalysts had to rely on exploiting the [[#Operating shortcomings|operator weaknesses]] described below, particularly the cillies and the [[Herivel tip]].

After the June Franco-German armistice, the Polish cryptological team resumed work in France's southern ''Free Zone'',<ref>{{cite journal |title=Forgotten heroes of the Enigma story |last=Baker |first=Joanne |date=September 2018 |journal=Nature |volume=561 |issue=7723 |pages=307–308 |bibcode=2018Natur.561..307B |doi=10.1038/d41586-018-06149-y |pmid=30214032 |s2cid=52272490 |url=https://www.nature.com/articles/d41586-018-06149-y}}</ref> although probably not on Enigma.<ref>It is not clear whether, after the June 1940 fall of France, the Cipher Bureau broke Enigma. Rejewski, the principal Polish source, wrote in a posthumously published 1980 paper that at [[Cadix]] "We worked on other ciphers, no longer on Enigma". ({{Harvnb|Kozaczuk|1984|p=270}}). Colonel [[Stefan Mayer]] of Polish Intelligence, however, mentioned the Poles breaking "interesting [machine-enciphered messages] from [Germany's 1941] Balkan campaign coming [in over] the 'Luftwaffe' network..." ({{Harvnb|Kozaczuk|1984|p=116}}). And French intelligence Gen. Gustave Bertrand wrote of Enigma having been read at Cadix. ({{Harvnb|Kozaczuk|1984|p=117}}). Tadeusz Lisicki, Rejewski's and Zygalski's immediate chief later in wartime England but sometimes a dubious source, wrote in 1982 that "Rejewski in [a letter] conceded that Bertrand was doubtless right that at Cadix they had read Enigma, and that the number given by Bertrand, of 673 [Wehrmacht] telegrams, was correct.... The British did not send keys to Cadix; these were found using various tricks such as the sillies [and] Herivel tip described by Welchman, Knox's method, as well as others that Rejewski no longer remembered". ({{Harvnb|Kozaczuk|1984|p=117}}).</ref> Marian Rejewski and Henryk Zygalski, after many travails, perilous journeys, and Spanish imprisonment, finally made it to Britain,<ref>The third mathematician, Jerzy Różycki, had perished together with three Polish and one French colleague in the 1942 sinking of the passenger ship ''Lamoricière'' as they were returning to France from a tour of duty in [[Algeria]].</ref> where they were inducted into the Polish Army and put to work breaking German ''[[SS]]'' and ''[[Sicherheitsdienst|SD]]'' hand ciphers at a Polish signals facility in [[Boxmoor]]. Due to their having been in occupied France, it was thought too risky to invite them to work at Bletchley Park.<ref>{{Harvnb|Kozaczuk|1984|pp=148–55, 205–9}}</ref>

After the German occupation of [[Vichy France]], several of those who had worked at ''PC Bruno'' were captured by the Germans. Despite the dire circumstances in which some of them were held, none betrayed the secret of Enigma's decryption.<ref>{{Harvnb|Kozaczuk|1984|p=220}}</ref>