The U.S. Post Office Department began experimenting with airmail in 1911 and expanded trial flights over the next several years, but the lack of suitable aircraft delayed regular service until Congress funded experimental routes in 1918 and the Army Signal Corps lent planes and pilots. Early flying was difficult because airplanes lacked radios, instruments, and navigational aids, and pilots often had to rely on dead reckoning and make weather-forced landings. A 1919 transcontinental air race organized by General William "Billy" Mitchell helped demonstrate a practical cross-country route that the Post Office later adopted. The transcontinental airmail line was built in stages from New York to Cleveland in 1918, Cleveland to Chicago in 1919, Chicago to Omaha in 1920, and Omaha to San Francisco on September 8, 1920, with stops including North Platte, Cheyenne, Rock Springs, Salt Lake City, Elko, and Reno. Cheyenne was chosen as a major division point because of its central position between Chicago and San Francisco, its location near the lowest crossing of the Rocky Mountains, and its access to the Union Pacific Railroad, which also served as a daytime landmark for pilots. After the city and Laramie County secured the present airport site and built a hangar, the U.S. Air Mail Service began operations in Cheyenne on September 8, 1920, when Buck Heffron departed westward with 400 pounds of mail; James "Jimmy" Murray arrived from the east the next day and carried the first eastbound mail from Cheyenne on September 13, helping complete the inaugural circuit of the first transcontinental air service. At first, mail was flown by day and carried by train at night, cutting 22 hours from all-rail service. Radio stations began to be installed at flying fields in 1920, and by November 1921 mail was flown both day and night. Congress then funded further expansion, adding landing fields and equipping routes with towers, beacons, searchlights, boundary markers, and improved aircraft instruments and lights. The first commercial airline air mail flight took place in February 1926, and soon afterward the Post Office transferred its airmail facilities to the Department of Commerce.