Horace Porter entered the United States Military Academy at West Point in 1855.  He maintained a high standing in the class during his 5 years and was especially proficient in English, mathematics, French, chemistry, engineering, ethics, philosophy, and the science of war.  Cadet Porter met Sophie McHarg in 1859 and it was "love at first sight,"  as she was beautiful and charming.  On July 1, 1860 Horace Porter graduated third amongst the "five honor men" of his West Point class.

In the fall of 1860 Lieutenant Porter received his orders to report at Watervliet Arsenal at Troy on the Hudson.  The summer at Watervliet was naturally a busy one and at one time Porter found himself in command of the arsenal.