 Initially he had wanted to join the Artillery, but shortly after graduation, a classmate convinced him to choose the Engineers.He was commissioned as a brevet second lieutenant in the U.S. Army on July 1, 1854, second lieutenant on October 2, 1855 and first lieutenant on July 1, 1857.In 1855, Abbot was assigned to work with Lieutenant Robert Williamson's Pacific Railroad Survey in California and Oregon.