In January 1960, the Mooney company convinced Ralph Harmon to leave McDonnell Aircraft in St. Louis, Missouri, and take over management of the engineering efforts. He insisted on replacing the wood in the M20 with aluminium, and the all-metal M20B was completed by the end of 1960, less than a year after his arrival. In 1961, the company sold 222 M20B airplanes. The following year, the M20C was introduced and 336 were sold that year. Also known as the Mark 21 and later the Ranger, the M20C had several improvements over the M20B, including greater deflection on control surfaces, reduced cowl flap openings for better engine cooling, improved exhaust scavenging with a Hanlon and Wilson exhaust system, new battery access door, more powerful landing light, lightweight floor, an increased gross weight of , lighter empty weight, new instrument panel layout, and a higher maximum flap angle of 33 degrees.