There are a number of unmanned vehicles that flew at supersonic speeds during this period. In 1933, Soviet designers working on ramjet concepts fired phosphorus-powered engines out of artillery guns to get them to operational speeds. It is possible that this produced supersonic performance as high as Mach 2, but this was not due solely to the engine itself. In contrast, the German V-2 ballistic missile routinely broke the sound barrier in flight, for the first time on 3 October 1942. By September 1944, V-2s routinely achieved Mach 4 (1,200 m/s, or 3044 mph) during terminal descent.