Operation Crossbow - Heavy Sites - Watten

The 'Heavy Sites' were the large bomb proof installations in northern France associated with the German V Weapon programme.
 
Watten was the first of the sites to be spotted on photographic reconnaissance in May 1943 and showed that some kind of excavations had begun in Foret d'Eperlecques. Ten days after the RAF attack on Peenemunde, in August 1943, 185 Flying Fortresses of the US Eighth Air Force attacked the Watten site. This had been timed on the advice of Sir Malcolm McAlpine, the civil engineer, to occur at the most critical stage of construction - when the concrete had been poured but not hardened - and resulted in the Germans abandoning that part of the site.
 
By the end of the year they began construction work had begun on new and stronger buildings to the south of the site. When the site had almost been completed it was targetted by the RAF who used 'Tallboy' bombs, designed by Barnes Wallis.
 
The site was eventually abandoned by the Germans in July 1944, following the Allied invasion of northern France in early June.