Herman worked part-time to pay his school tuition, then in 1831 was appointed to the United States Military Academy at the age of 14 by President Andrew Jackson.

In the 1870 census, Louis, Herman, Charles, Frank and Alex were living at home with their parents in Philadelphia's Ward 10, as were their sisters Mary and Ella.

[3] At 19, he was appointed Assistant Engineer in the state service and surveyed the line from Gettysburg to the Potomac across the South Mountain, a right-of-way that became part of the Western Maryland Railroad.

"[1] Haupt was promoted to brigadier general of volunteers on September 5, 1862, but he initially refused the appointment, explaining that he would be happy to serve without official rank or pay, but he did not want to limit his freedom to work in private business – and he privately bridled at the protocols and discipline of Army service.

Its range of operation was extended to Tennessee and it accompanied Sherman's thrust through Georgia under the direction of Colonel William Wierman Wright and division engineer Eben C.

[8] Haupt also experimented with bridge demolition using "torpedoes", as mines were called at the time, inserted in holes drilled in trusses.

[10] Offered promotion again in early autumn 1863, Haupt hinged his acceptance on three conditions: that a central Bureau of U.S. Military Railroads be established to inspect, direct, and receive reports concerning construction and operation of all military railroads; difficulties with commanding generals be avoided through consultation and cooperation within their departments; the chief of the bureau should be free to move wherever his personal presence was necessary or to attend to whatever public or private business required his attention.

After the Battle of Gettysburg, Haupt boarded one of his trains and arrived at the White House on July 6, 1863, becoming the first to inform President Lincoln that General Robert E. Lee's defeated Confederate army was not being pursued vigorously by Union Major General George G. Meade.

His two main principles were that the military should never interfere with the efficient running of the railroad and that rolling stock should be emptied and returned promptly to enable their re-use as transport.

Haupt became wealthy from investments in railroads, mining, and Pennsylvania real estate, but eventually lost most of his fortune, in part due to political complications involving the completion of the Hoosac Tunnel.

He invented a drilling machine that won the highest prize of the Royal Polytechnic Society of Great Britain and was the first to prove the practicability of transporting oil in pipes.