[2] Andrew Ernst was himself the son of a recent immigrant, a burgomaster who had fled Germany during the Napoleonic Wars and afterward settled in the Ohio River valley.

[2] The younger Ernst was an excellent student, admitted to Harvard in 1858, and left that place of learning to accept an appointment from Ohio to the United States Military Academy at West Point, New York, in 1860.

[4] When the American Civil War broke out, plebe Ernst stayed at the academy with the Union-born cadets while most southerners left for the Confederacy.

[9] Ernst married Elizabeth Amory Lee in late 1866,[2] and spent the years immediately after the war working on constructing fortifications on the Pacific coast, and remained so occupied until 1868.

While teaching cadets and writing the Manual of Practical Military Engineering, Ernst found time to author articles for Johnson's Encyclopedia[9] and raise his two daughters Helen Amory and Elizabeth Lee.