The British cryptological centre whose head, Alastair Denniston, took part in the meeting at Pyry in July 1939.
According to GCHQ, the knowledge gained in Poland changed GC&CS's approach to the cryptanalysis of Enigma.1
According to GCHQ, the school was set up around 1919 as a single institution responsible for communications intelligence, by merging military units from the First World War. In 1939, after moving to Bletchley Park, it was given the cover name GCHQ, under which its successor – today's GCHQ agency – operates.2
Gill Bennett, a historian at the British Foreign Office, points out that GC&CS's achievements were particularly valuable because on the eve of the war MI5 and MI6 had modest resources. In her view, the Polish results, handed over at Pyry on 26 July 1939, shortened the British attack on Enigma by at least a year.3
More in the operation card: Breaking Enigma.
Sources
- GCHQ, The Pyry Forest meeting
- GCHQ, 100 years of GCHQ (2019)
- Gill Bennett, blog of the UK Foreign Office historians (history.blog.gov.uk), What’s the context? Polish cryptologists reveal they have cracked the Enigma code, 26 July 1939 (26.07.2019)
Checked: 4 November 2026