Sigint Liaison with Finland

 

The UK now has a Defence Agreement with Finland and Sweden, and will soon be formally allied to both countries in NATO. It is not well known that for a short period in the Second World War the UK and Finland found themselves on the same side: our enemy's enemy was our friend and in spite of the alliance between Nazi Germany and the USSR, German occupation of Poland, Denmark and Norway, the Soviet occupation of the Baltic States and the part of Poland the Germans had agreed to let them have, and Swedish neutrality, the UK and Finland enjoyed a Sigint partnership for just over a year.

British Sigint had had relationships with the French, Italians and Americans during the First World War. These had all disappeared by the time GC&CS was formed on 1 November 1919. RAF Sigint did its own deal with the Estonian military Sigint authorities, and for most of the 1930s equipped and trained the Estonians in return for Estonian intercept logs of traffic of the Soviet Air Force, though this ended in 1939. In the 1930s, under the auspices of SIS a relationship was developed with the French to discuss Enigma, and from this grew the 'Enigma Relay', the exchange of information that led to Enigma becoming an exploitable cipher system.

This meant that GC&CS had become receptive to the idea that foreign Sigint services could be met as partners and early in 1940, this led to the idea that somebody should visit Finland to see whether the Finns were doing anything against the Soviet Union, the ally of Nazi Germany, that might benefit UK Sigint. At this point there was no dedicated UK effort against the Soviet military: an interservice cryptanalytical section would not be set up (in Wavendon, near Bletchley) until the summer of 1940.

Tiltman, the Head of the Military Section, went to Finland to meet the Finnish Sigint organisation, a meeting brokered by the SIS representative in Helsinki and the UK Military Attache. He arrived in Finland on March 1st 1940 and stayed for ten days most of which he spent with Major Hallamaa, the head of Finnish Army Sigint, at Kerava. Hallamaa showed Tiltman the whole of his organisation and expressed the willingness of the Finnish General Staff to cooperate fully in Sigint matters with the British.

The Finns were willing to exchange their knowledge of Russian codes and ciphers in return for the radios they were very short of. They needed 50 receivers, 6 DF sets and 6 high-powered transmitters to link their units in the field. The War Office in London confirmed that some of the equipment was available and the Finns handed over a forty page handbook on Russian Army and Naval communications.

The equipment was released on 15 April 1940, and the Finns were further informed that the UK would fund the Finnish purchase of further radio equipment in Sweden up to the value of £500. Some equipment arrived in Helsinki but when another GC&CS officer arrived in Finland to develop liaison on the Russian target he found that the Finns had only obtained 4 receivers, though a search while he was there produced three of the DF sets as well, and the Finns appeared satisfied that the British were acting in good faith. They agreed to provide Soviet intercept provided the British reciprocated: in the Finnish system the clerical effort involved would have to be justified to higher authority by a quid pro quo. They gave the UK the current encryption system being used by the Soviet Baltic Fleet as well as military systems which had become mainly readable. In return GC&CS offered its work on encryption systems used by the Soviet Navy Black Sea Fleet which was being taken in Palestine.

The exchange of intercepts was not straightforward. The air route between the UK and Finland was only open during the summer months, and the Finns were unwilling to open a new two-way radio link to the UK so the only way was to send the traffic by air to Stockholm from Helsinki in a diplomatic bag and to forward the traffic from there on commercial wireless circuits and vice versa. This would have worked if a Typex machine could have been sent to Stockholm and if sufficient Typex capacity had been installed at Sarafand to deal with the Black Sea traffic. However, there were significant problems in the supply of Typex, and by March 1941 Denniston argued that if only GC&CS could be allocated 10 lbs weight in the Stockholm daily bag the need for Typex would disappear, but neither Typex nor the 10 lbs of freight became available.

In spite of all the assurances it had given, the War Office did not actually send the rest of the radio equipment originally promised. It took until summer 1941 before this was sorted out and by then the situation had changed completely. The Germans declared war on Russia and a German mission was sent to Finland just as the final decision to send the missing sets was taken.

The last signal from Finland contained an assurance that they would not reveal to the Germans their Sigint cooperation with the UK and asked for an assurance that the British would not tell the Russians of Finnish cryptanalytical success against Russian systems. This assurance was given, and the Finns and the British each kept their promise (something perhaps easier for the British side than for the Finnish).

GC&CS developed its links with the US, and maintained its links with France and the exiled Poles until December 1942, but this marked the high water of non-Five Eyes cooperation. The Finnish experience had shown GCHQ that a buccaneering attitude to foreign relationships might bring results, but always at a potential cost of the partnership being prey to other considerations, and the dispersal of French and Polish cryptologists after the Nazi occupation of Vichy led to a new and cautious approach which would last for many years.