Conceptual work began in 1941, and final specifications were defined on November 2, 1942. The first models were being tested in March 1943, but a major setback occurred in August 1943 when Dr. Walter Thiel was killed during the Operation Hydra bombings, the start of the Operation Crossbow bombing campaign against V-2 production. After the first successful firing (the third prototype) on March 8, 1944, three Wasserfall trial launches were completed by the end of June 1944. A launch on January 8, 1945 was a failure, with the engine "fizzling" and launching the missile to only 7 km of altitude at subsonic speeds. The following February saw a successful launch which reached a supersonic speed of 770 m/s (2,800 km/h) in vertical flight. Thirty-five Wasserfall trial firings had been completed by the time Peenemünde was evacuated on February 17, 1945.