A 1933 graduate of B.M.C. Durfee High School, Zais attended the University of New Hampshire and graduated with a Bachelor of Arts in Political Science. During his freshman year, he studied at the Louisiana State University as a journalism major before transferring to UNH. In 1937 he was commissioned a second lieutenant in the United States Army Reserve. In 1940 he was a member of the original Parachute battalion later the 501st Parachute Infantry Regiment. During World War II, Zais was the commander of the 3rd Battalion and, later, executive officer of the 517th Parachute Infantry Regiment, fighting in Italy, in southern France, and in the Battle of the Bulge.