I don't want to sound sarcastic here, really I don't, but do you Schwere Luft know how that claim sounds?!!
The Germans in early 1945 manage to manufacture a double sonic aircraft using a rocket motor to get it aloft, and then running this aircraft on powdered coal dust (possibly with parrafin added) using a ramjet engine. They build the aircraft in Austia / Southern Germany and then ship the finished plane to Norway were it is launched from a mountian-top site in Norway and flown across neutral Sweden back to Germany and, more than once!
Post war however, this whole project "disappears" with nothing more heard of it. Cover up? No. Didn't happen; Yes.