Jacob Zeilin was appointed a second lieutenant in the Marine Corps in 1831. On June 10, 1864 he was appointed Colonel Commandant of the Marine Corps, the Corps’ 7th Commandant, and served in that position untile his retirement on October 31, 1976. For his faithful and efficient performance of duty in that billet during the Civil War, he was promoted to the rank of brigadier general on March 2, 1867, become the Marine Corps’ FIRST General Officer. He retired as a United States Marine Corps Brigadier General in 1867.