Private First Class Knowlton was a member of Company L, 3rd Battalion, 38th Infantry Regiment, 2nd Infantry Division. He was listed as Missing in Action while fighting the enemy near Kunu-ri, North Korea, on 28 November 1950. He was presumed dead on 31 December 1953. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Knowlton was awarded the Purple Heart, the Combat Infantryman's 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.