Sergeant Gillis was a member of the 27th Infantry Regiment, 25th Infantry Division. He was seriously wounded by the enemy in South Korea on 4 August 1950 and died of those wounds the following day.

Gillis was awarded the Purple Heart, the Combat Infantryman Badge, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.