Editing Cryptanalysis of the Enigma (section)

===Polish disclosures===
As the likelihood of war increased in 1939, Britain and France pledged support for Poland in the event of action that threatened its independence.<ref>{{citation |last=Chamberlain |first=Neville |author-link=Neville Chamberlain |date=31 March 1939 |title=European Situation (2.52 p.m.) |periodical=Hansard |publisher=UK Parliament |volume=345 |url=https://api.parliament.uk/historic-hansard/commons/1939/mar/31/european-situation-1 |access-date=3 January 2009}}</ref> In April, Germany withdrew from the [[German–Polish Non-Aggression Pact]] of January 1934. The Polish General Staff, realising what was likely to happen, decided to share their work on Enigma decryption with their western allies. Marian Rejewski later wrote:

{{blockquote|[I]t was not [as Harry Hinsley suggested, cryptological] difficulties of ours that prompted us to work with the British and French, but only the deteriorating political situation. If we had had no difficulties at all we would still, or even the more so, have shared our achievements with our allies as our contribution to the struggle against Germany.<ref name=RejewskiHinsleyP80/><ref>{{Harvnb|Kozaczuk|1984|p=64}}</ref>}}

At a conference near Warsaw on 26 and 27 July 1939, the Poles revealed to the French and British that they had broken Enigma and pledged to give each a [[Polish Enigma double|Polish-reconstructed Enigma]], along with details of their Enigma-solving techniques and equipment, including Zygalski's perforated sheets and Rejewski's [[bomba (cryptography)|cryptologic bomb]].<ref>{{Harvnb|Erskine|2006|p=59}}</ref> In return, the British pledged to prepare two full sets of [[Zygalski sheets]] for all 60 possible wheel orders.<ref>{{Harvnb|Herivel|2008|p=55}}</ref> Dilly Knox was a member of the British delegation. He commented on the fragility of the Polish system's reliance on the repetition in the indicator, because it might "at any moment be cancelled".<ref>{{Harvnb|Copeland|2004|p=246}}</ref> In August, two Polish Enigma doubles were sent to Paris, whence [[Gustave Bertrand]] took one to London, handing it to [[Stewart Menzies]] of Britain's [[Secret Intelligence Service]] at [[London Victoria station|Victoria Station]].<ref>{{Harvnb|Bertrand|1973|pp=60–61}}</ref>

Gordon Welchman, who became head of [[Hut 6]] at Bletchley Park, wrote:

{{blockquote|Hut 6 Ultra would never have gotten off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military version of the commercial Enigma machine, and of the operating procedures that were in use.<ref>{{Harvnb|Welchman|1984|p=289}}</ref>}}

[[Peter Calvocoressi]], who became head of the Luftwaffe section in Hut 3, wrote of the Polish contribution:

{{blockquote|The one moot point is—how valuable? According to the best qualified judges it accelerated the breaking of Enigma by perhaps a year. The British did not adopt Polish techniques but they were enlightened by them.<ref>{{citation |last=Calvocoressi |first=Peter |author-link=Peter Calvocoressi |title=Credit to the Poles |newspaper=The Times |location=London |page=13 |date=23 March 1984}}</ref>}}