Following the cessation of hostilities, Mitchell remained in the Army. From 1900 to 1904, Mitchell was posted in the District of Alaska as a lieutenant in the Signal Corps. On May 26, 1900, the United States Congress appropriated $450,000 to establish a communications system connecting the many isolated and widely separated U.S. Army outposts and civilian Gold Rush camps in Alaska by telegraph. Along with Captain George C. Brunnell, Lieutenant Mitchell oversaw the construction of what became known as the Washington-Alaska Military Cable and Telegraph System (WAMCATS). He predicted as early as 1906, while an instructor at the Army's Signal School in Fort Leavenworth, Kansas, that future conflicts would take place in the air, not on the ground.