Haupt graduated from the U.S. Military Academy, West Point, N.Y., in 1835 but resigned his army commission to enter the rapidly expanding field of railroad engineering, in which he soon won a leading place. In 1855 he was called on to assist in the ambitious project of constructing a railroad tunnel through the Hoosac Range at North Adams, Mass. Despite many obstacles, both technical and financial, he pushed the work a considerable distance before being called to Washington, D.C., in 1862 to take charge of military rail transportation in the American Civil War. The tunnel was completed in 1873. Later he returned to railroad engineering as general manager of the Northern Pacific Railway Company during the line's completion to the West Coast. He also played a major role in introducing compressed air machinery into mining and tunneling. Among his many books, the most important were General Theory of Bridge Construction (1851), Military Bridges (1864), and Tunneling by Machinery (1876).