Spies in the Sky: The Secret Battle for Aerial Intelligence during World War II

At the centre of Allied Intelligence operations during the Second World War was the work carried out at two country houses just outside London. Both were near to railway lines with easy access to the capital. Moreover, both operations soon outgrew the country houses themselves, and brick and concrete huts sprawled out across the grounds and gardens. The work carried out at one of these country houses, Bletchley Park, is now well known. There have been novels, movies and dozens of books about Bletchley Park. However, the story of the top-secret intelligence work carried out at RAF Medmenham and of the equally remarkable group of boffins and mavericks who were gathered there is still relatively unknown. Following on from work done in the First World War, the RAF assembled an unusual group of eccentrics, boffins, academics and inventors who developed a completely new science of decoding and reading aerial photographs. The work carried out at Medmenham was arguably even more important than that at Bletchley Park, and it was said that 80% of all intelligence in the war came from aerial photography.

Hundreds of brave reconnaissance pilots flew for hours across occupied Europe every day to bring back aerial photographs for the Photo Interpreters (PIs) at Medmenham. The PIs could analyse the movement of ships and trains and see what cargoes were being freighted around Europe. They could look down into factories and see the war weapons, aircraft and machines that were being produced. They could see from the enemy's shipyards what submarines and other vessels were under construction and so predict the strength of the German Navy up to a year ahead. Moreover, by studying every new building, they could find the location of secret factories and missile launch sites and then direct Allied bombers to them. After every raid, they could assess the damage and report whether the factory or military installation had been put out of action or whether it needed to be bombed again. There was almost nothing of military significance taking place in Nazi-occupied Europe that escaped the spies in the sky.

This is the history of how a secret science was developed to read and measure aerial imagery, how the use of 3D photographs was developed and how a mass of data was built up about the German war economy. An extraordinary group of men worked at Medmenham, and an even more remarkable group of women worked there.