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Poland’s Decisive Role in Cracking Enigma and Transforming the UK’s SIGINT Operations

Tony Comer
Commentary, 27 January 2021
UK, History, Intelligence
Enigma was broken at Bletchley Park because of the Polish decision in 1939 to share all they knew. That led to a radical transformation of British signals intelligence.

In July 2014, Iain Lobban, the director of GCHQ, the UK's signals intelligence (SIGINT) agency, joined his Polish and French counterparts in Warsaw to commemorate the 75th anniversary of a historic meeting between British, Polish and French SIGINT specialists. In July 1939, the Polish intelligence service invited British and French cryptanalysts to Warsaw and, with the imminence of war becoming apparent, shared everything they knew about Enigma, the cipher machine relied on by the German armed forces.

Polish Help as the Foundation of Success

The consequences of this decision were far-reaching, but before looking at them, I want to highlight something which usually gets crowded out of the popular British narrative about Bletchley Park, in which Alan Turing and a small number of mathematical geniuses break Enigma and win the war. British cryptanalysts had completely failed to discover one of the variables of the military variant of Enigma without which a solution was impossible, and there is no reason to suppose that they would ever have got there, as the one person who guessed at the right answer was laughed out of court without the suggestion even being tested. The information supplied by the Poles was the foundation on which Bletchley Park’s success against Enigma was built.

The Consequences

The centralisation of SIGINT. The expectation of the three armed services in 1939 was that they would each have their own separate SIGINT organisations. When the British Expeditionary Force (BEF) deployed to France, for example, its SIGINT organisation was given formal permission to use its collection and processing capabilities to serve the BEF without any reference back to London. In this framework the Government Code and Cypher School (GC&CS), as GCHQ was called then, at Bletchley Park would only be responsible for solving new encryption systems and passing the information needed to decrypt them to SIGINT stations at home and overseas. But this would not produce results on Enigma. It was not just that the technical solution to Enigma key recovery was too expensive to permit a multiplication of capability for each service: it was because Enigma needed a target-specific response and had to be attacked as a single cryptanalytic problem.

An intelligence centre, not just a cryptanalytic bureau. This led to Bletchley Park tasking service SIGINT units directly and those units forwarding the intercepted messages to Bletchley where they would be decrypted. Decrypts with intelligence value were then passed, not back to the intercept units, but to the intelligence divisions of the single service ministries. Traffic analysis, which alongside cryptanalysis was the principal SIGINT-specific form of intelligence analysis, was centralised in Bletchley Park to complement the cryptanalytic effort against Enigma. By the end of the war, SIGINT was an activity completely controlled by GCHQ.

The industrialisation of SIGINT. Some mechanical arithmetical systems had been used since the First World War, but the Bombe was the first electromechanical device used in the UK. It was designed by Alan Turing to recover Enigma settings. Its name came from the 'Bomba', the first electromechanical cryptanalytic machine which was designed by Poland, details of which were handed to the British and French in July 1939 – Turing's design was original, but it was inspired by the Polish device. It is clear that it was the Polish use of electromechanical technology that moved cryptanalysis into the industrial age. 'C', the chief of the Secret Intelligence Service, put £100,000 (about £25.5 million today) into the development of Turing's Bombe, and eventually over 200 were built. This fundamentally changed the way SIGINT worked: machine-based cryptanalysis became the heart of the mission. Although the Bombes only worked against Enigma, and therefore had no intelligence value after VE Day, the technological mindset that produced the Bombe evolved and led to the development of Colossus, a proto-computer to decrypt enciphered German teleprinter traffic, which in turn presaged GCHQ's post-war emergence as a fundamentally technological organisation.

The need for partnerships. There had been cooperation between UK cryptanalysts and their French and, eventually, American counterparts during the First World War, but all contacts ended with the signature of the peace treaty in 1919. There were a couple of attempts at international cooperation in the 1930s but it took the threat of war, the seeming impossibility of breaking the primary encryption system used by the German military and an invitation from the French to persuade the UK to collaborate internationally, first with France, and after with Poland.

A partnership between two countries in SIGINT can never be as distant or as transactional as relationships in other areas of intelligence can be, because they are much more revelatory about each side's capabilities, sources and methods. By definition, a SIGINT partnership has to be a close one. Today, GCHQ's predominant overseas relationship is with the US as part of the Five Eyes community. It is a relationship that was codified 75 years ago in March 1946, but that began in February 1941. Its roots are in the realisation in 1939 that UK SIGINT needed the insights offered by Poland: that they were stronger in cooperation than in isolation.

Communications security. On its foundation in 1919, GC&CS was given the role of providing advice (if requested) about communications security to the UK government. Between the world wars, the GC&CS predominantly targeted the diplomatic codebooks of foreign countries, so when called upon to advise on communications security they simply recommended the use of systems that they had been unable to penetrate. This is an under-researched area but poor practices by the services, allied to poor advice from GC&CS, was calamitous. By June 1940, the Germans could read all British military encryption systems with the single exception of Typex, an electromechanical cipher machine designed by Britain’s Air Ministry and based on Enigma.

The new cryptanalysts, mathematicians like Alan Turing who were recruited from universities, were much better qualified to give advice than their predecessors and this advice made Typex sufficiently secure that no technology could break its encryption. Their advice also improved the medium- and low-grade systems used by the services when deployed.

The Relay Race Which Started in Poland

We can think of Poland’s information exchange in 1939 as a relay race: the Poles ran the first lap brilliantly and passed the baton to the British, who were able to build on Polish success to run the next lap. Even in 2014 it was still difficult for some British commentators to accept that Bletchley Park's Enigma success was built on Polish foundations. Since then, Dermot Turing has written X, Y & Z, which tells this remarkable story in detail.

There is still scope, however, to reflect further. GC&CS transformed completely during the Second World War from being a cryptanalytical bureau specialising in diplomatic reporting to a fully-fledged SIGINT agency, working across all areas of interception and producing wanted intelligence against the widest range of enemy activity. After the war, the organisation retained both the technological focus it had developed and the ability to adapt to new circumstances and exploit new opportunities.

I do not think it is fanciful to say that this would not have happened without the Polish contribution.

Tony Comer joined GCHQ in 1983 and retired in 2020 having been the in-house historian for the last 11 years.



The views expressed in this Commentary are the author's, and do not represent those of RUSI or any other institution.

BANNER IMAGE: Polish cryptologists. Left to right: Henryk Zygalski, Jerzy Różycki and Marian Rejewski. Courtesy of the archive of Janina Sylwestrzak, daughter of Marian Rejewski. With gratitude to the Polish Embassy, London, for facilitating access to this record. 

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