Zeilin was commissioned in the Marine Corps as a
second lieutenant on October 1, 1831.
Mexican–American War During the
Mexican–American War, Zeilin commanded the
Marine Detachment assigned to USS
Congress, which was attached to Commodore
Robert F. Stockton's force. He took part in the
Conquest of California and fought in the conquest and occupation of
Santa Barbara and
San Pedro, as well as the
Siege of Los Angeles and the
Battle of La Mesa.
Interwar period After the war with Mexico, Zeilin proceeded to Norfolk, Virginia, where he served for a time, then to New York. He remained at New York until June 1852. He was selected to accompany Commodore
Matthew C. Perry as Fleet Marine Officer in the Perry Expedition to Japan, serving with the Marine Detachment in . With elaborate ceremonies, the Marines under his command took a prominent part in the expedition. He was the second person to set foot on shore at the formal landing of the naval forces at
Kurihama, Yokosuka, Japan on 14 July 1853, and was one of those later accorded special honor for his part in the expedition that opened the doors of Japan to the outside world. Zeilin retired from the Marine Corps on November 1, 1876, after serving over forty-five years as a Marine Corps officer. When considering his time at West Point, he served over 49 years in uniform. ==Personal life==