The idea of a flying disc in modern history dates back at least to 1898 when, on June 14, F.A. Jone was granted US patent 605579 for a disc shaped flying machine. From the relative size of different parts of the aircraft the design is estimated to be at least 60 feet high. There's no record that Jone ever got his design off the drawing board and into production, but humanity did not have to wait very many years to witness the first disc shaped aircraft get off the ground.
According to the Smithsonian Institution and Fédération Aéronautique Internationale (FAI), the Wright brothers made the first sustained, controlled, powered heavier-than-air manned flight at Kill Devil Hills, North Carolina, on December 17, 1903.
Apparently encouraged by his earlier "success" of the XM-2 and XM-3 Dr Moller began construction of the XM-4 in 1970. The XM-4 featured eight Fichtel-Sachs rotary engines which surrounded the passengers in a circular pattern and debuted in 1974. At this point Moller had been making unsuccessful flying saucers for 8 years and one wonders where his financial backing was sourced and who might want the public to believe that people are not capable of making high performance disc shaped aircraft.
The TV propaganda machine rolled on and on. After 10 years of planning, SHADO officially got into operation on 16 September 1970 and encountered its first UFO.