Private First Class Gayhart was a member of Company H, 3rd Battalion, 5th Marines, 1st Marine Division. He was listed as Missing in Action while fighting the enemy at "Outpost Vegas" in South Korea on 26 March 1953. He was presumed dead on 26 March 1954. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Gayhart 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.