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Operation Crossbow - V1 Bois Carre Sites

At the beginning of November 1943 a message was received in London, from a secret agent, that a French construction firm had been employed by the Germans to work on eight construction sites. These were located in the Pas de Calais region of northern France, and were promptly covered by a photographic reconnaissance mission, which recognised that all the construction work was to a standard design and deliberately concealed in woods. Since the first of these places to be fully studied by the ACIU photographic interpreters at RAF Medmenham was at Bois Carré, all similar sites were given that name.
These first Bois Carré installations all had noticeable features in common. In particular three buildings that had the appearance of a ski-board lying on its side - which prompted the interpreters to nickname them the ski sites - and a platform lined up in the direction of London. In the weeks that followed, the Crossbow team probed sortie after sortie, eventually locating ninety-six sites. By comparing these with aerial photography of Peenemunde, they were able to prove a connection.
With so many under construction, and the assessment that a site could become operational within 120 to 140 days of construction starting, the Crossbow team produced a points system to determine when a site should be attacked. Once a site had been 70% built it was included in the list of bombing targets and attacked. By March 1944 all the known Bois Carré sites had been heavily bombed and those nearing completion destroyed.