In 1917, Iaccaci and his brotherAugust joined the Royal Flying Corps in Canada. In April of 1918, they were both assigned to 20 Squadron at Calais where they flew the Bristol Fighter. Each of them was credited with 17 victories while serving with this squadron.

Distinguished Flying Cross (DFC)

"A bold and successful fighter, who on four offensive patrols has accounted for six enemy aeroplanes; two he shot down himself, and four were destroyed with the assistance of his observer. In these several encounters the formation in which Lieutenant Iaccaci was serving was engaged against heavy odds." DFC citation, London Gazette, September 21, 1918