As the opening attack of the British Operation Crossbow, the Operation Hydra air-raid attacked the HVP's "Sleeping & Living Quarters" (to specifically target scientists), then the "Factory Workshops", and finally the "Experimental Station" on the night of August 17/18, 1943. The Polish janitors were given advance warning of the attack, but the workers could not leave due to SS security and the facility had no air raid shelters for the prisoners. Fifteen British and Canadian airmen who were killed on the raid were buried by the Germans in unmarked graves within the secure perimeter. Their recovery at the end of the war was prevented by the Russians authorities and the bodies remain there to this day.