landing and the fuselage having been on fire, it proved to official circles that an aircraft could be flown satisfactorily with a back-thrust system through the rear. At the same time, Hellmuth Walter's experiments into hydrogen peroxide based rockets were leading towards light and simple rockets that appeared well-suited for aircraft installation. Also the firm of Hellmuth Walter at Kiel had been commissioned by the RLM to build a rocket engine for the He-112, so there were two different new rocket motor designs at Neuhardenberg: whereas von Braun's engines were powered by alcohol and liquid oxygen, Walter engines had hydrogen peroxide and calcium permanganate as a catalyst. Von Braun's engines used direct combustion and created fire, the Walter devices used hot vapors from a chemical reaction, but both created thrust and provided high speed. The subsequent flights with the He-112 used the Walter-rocket instead of von Braun's; it was more reliable, simpler to operate, and safer for the test pilot, Warsitz. Slave labor SS General Hans Kammler, who as an engineer had constructed several concentration camps, including Auschwitz, had a reputation for brutality and had originated the idea of using concentration camp prisoners as slave laborers in the rocket program. Arthur Rudolph, chief engineer of the V-2 rocket factory at Peenemünde, endorsed this idea in April 1943 when a labor shortage developed. More people died building the V-2 rockets than were killed by it as a weapon. Von Braun admitted visiting the plant at Mittelwerk on many occasions, and called conditions at the plant "repulsive", but claimed never to have personally witnessed any deaths or beatings, although it had become clear to him by 1944 that deaths had occurred. He denied ever having visited the Mittelbau-Dora concentration camp itself, where 20,000 died from illness, beatings, hangings, and intolerable working conditions. Some prisoners claim von Braun engaged in brutal treatment or approved of it. Guy Morand, a French resistance fighter who was a prisoner in Dora, testified in 1995 that, after an apparent sabotage attempt, von Braun ordered a prisoner to be flogged, while Robert Cazabonne, another French prisoner, claimed von Braun stood by as prisoners were hanged by chains suspended by cranes. However, these accounts may have been a case of mistaken identity. Former Buchenwald inmate Adam Cabala claims that von Braun went to the concentration camp to pick slave laborers: ... also the German scientists led by Prof. Wernher