of Peenemünde's Camp Trassenheide in early 1943 provided maps, sketches and reports to Polish Home Army Intelligence, and in June 1943 British intelligence had received two such reports which identified the "rocket assembly hall", "experimental pit", and "launching tower". The Allies also received information about the V-1 and V-2 rockets and the production sites from the Austrian resistance group around the priest Heinrich Maier. The group later discovered by the Gestapo was in contact with Allen Dulles, the head of the US secret service OSS in Switzerland, and informed him about the research in Peenemünde. As the opening attack of the British Crossbow operations against German rocket weapons, the Operation Hydra bombing 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. A year later on July 18, August 4, and August 25, the U.S. Eighth Air Force conducted three additional Peenemünde raids to counter suspected hydrogen peroxide production. Evacuation As with the move of the V-2 Production Works to the Mittelwerk, the complete withdrawal of the development of guided missiles was approved by the Army and SS in October 1943. On August 26, 1943, at a meeting in Albert Speer's office, Hans Kammler suggested moving the A-4 Development Works to a proposed underground site in Austria. After a site survey in September by Papa Riedel and Schubert, Kammler chose the code name Zement (cement) for it in December, and work to blast a cavern into a cliff in Ebensee near Lake Traunsee commenced in January 1944. To build the tunnels, a concentration camp (a sub unit of Mauthausen-Gusen) was erected in the vicinity of the planned production sites. In early 1944, construction work started for the test stands and launching pads in the Austrian Alps (code name Salamander), with target areas planned for the Tatra Mountains, the Arlberg range, and the area of the Ortler