Private First Class Milligan was a member of Company B, 1st Battalion, 5th Marines, 1st Provisional Marine Brigade. He was Killed in Action defending his position at the Pusan Perimeter in South Korea on 18 August 1950.

Milligan was awarded the Purple Heart, the Combat Action Ribbon, 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.