A megahertz is one million (or 106) hertz.
See hertz, kilohertz (one thousand hertz), gigahertz[?] (109 hertz), terahertz[?] (1012 hertz), and petahertz[?] (1015 hertz).
... road cars and its success in early Grand Prix racing, winning the first ever Monaco Grand Prix and with driver Jean-Pierre Wimille[?] they won the 1937 and 1939 24 hours ...