The Ford Trimotor Airmail Plane
In 1925, automobile giant Henry Ford won a contract to fly mail between Chicago and Detroit and Cleveland. At first, Ford used airplanes his company had been using to transport automobile parts between assembly plants. In 1927, his company produced the Ford Trimotor aircraft. Made of a new material, duralumin, the Trimotor was one of the first all metal airplanes.
Designed to carry passengers as well as mail, the Trimotor could carry 12 passengers along with a cargo of mail. As with other contract carriers in the 1920s and 1930s, Ford's airmail contract paid enabled the company to grow and expand. Passenger service took a few more years to catch on.
While Western eventually added two M-4s to its fleet of six M-2s, the M-4 saw more extensive service with National Air Transport (later United Air Lines) from 1927 to 1930 on the Chicago-New York route. National Air Transport modified all of its M-3s into the M-4 configuration and eventually had 24 Douglas mailplanes on its roster, to become the largest operator of this type in commercial service.