Corporal Tsuboi was a member of Headquarters and Service Company, 89th Medium Tank Battalion, 25th Infantry Division. He was Killed in Action while fighting the enemy in North Korea on 13 December 1951. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

For his leadership and valor, Corporal Tsuboi was awarded the Bronze Star Medal, the Purple Heart, 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.