Eglin joined the Indiana National Guard in 1911 while a student at Wabash College, and first began federal service in June 1916, serving on the U.S. border with Mexico.

After earning his rating as a pilot and a commission in the Aviation Section, U.S. Signal Corps, Eglin remained at the school as a flying instructor.

After a four-year tour at the ACTS as an instructor and department director, Eglin was promoted to lieutenant colonel and assigned to the headquarters of the GHQ Air Force, where he was serving as a staff officer at the time of his death.

Lucille Eglin perished in a house fire in Washington D.C. two years to the day after her husband's death and was buried next to him at Arlington National Cemetery.

When the United States entered World War I in April 1917, Eglin earned a Reserve commission in the U.S. Army as a Second Lieutenant and was sent off to pilot training.

However, like many American military fliers during the war years, he was unable to get a combat assignment to Europe prior to the November 1918 Armistice and remained stateside as an instructor pilot.