Although it was officially formed in July 1940, the SOE (Special Operations Executive) had come to 1938 with the merger of 3 existing, top secret departments shortly after Germany annexed Austria.
Churchill's Secret Army was instructed to "Set Europe Ablaze".
SOE agents were sent to various Nazi occupied countries to both cause havoc behind German lines and also attempt to uncover local resistance groups they could work with when the time for invasion came.
Theatres of Operation included France, Belgium, Poland, Germany, Yugoslavia, Greece, Hungary, Albania, Czechoslovakia, Norway, Denmark, Romania, Abyssinia and the Far East.
As agents had to operate deep in occupied territory and they were recruited from a variety of social class and background.
The main requirement was that the prospective agent had detailed knowledge of the country they would operate in and able to pass as a native of that country.
Therefore, those with dual nationality were highly sought after.
The iconic plane used by the SOE in France was the Westland Lysander.
It was a small plane which made it a lot more difficult to see and was robust enough to land on makeshift landing strips.
It was used to ferry agents to and from the UK as well as picking up people who needed to be debriefed in London.
Airmen who had been shot down were also sometimes returned to the UK by Lysander.
Among the SOE numbers were also female agents and around 30% of the female agents sent into France from Section F, did not return.
The types of operations in each country varied.
For example, in Poland, there was little need to stir up the location population as there was already widespread hatred of the Nazis.
This was in contrast to areas such as Vichy France which collaborated with the occupying forces and the risk of SOE agents being doubled crossed was greatly increased.
Throughout World War II, the SOE had used around 13,000 people who directly supported or supplied somewhere in the region of 1 million operatives.