[2] During the U.S. Civil War, he served as captain of the Pocahontas and rescued Major Robert Anderson and Union troops after the bombardment of Fort Sumter.

[1] Gillis was a charter member of the Historical Society of Delaware in 1864 and donated many of his personal items collected over years of Navy service.

[2] After the death of Admiral Samuel Francis DuPont in 1865, Gillis became the highest-ranking military officer from Delaware.

[1] He completed his career serving at the New York and Philadelphia Navy Yards and was promoted to commodore before his retirement in 1866.

[2] He was a member of the Pennsylvania Commandery of the Military Order of the Loyal Legion of the United States and was assigned insignia number 267.