Sergeant First Class Mehmen was a member of Battery D, 82nd Anti-Aircraft Artillery (Automatic Weapons) Battalion, 2nd Infantry Division. He was taken Prisoner of War while fighting the enemy in South Korea on 13 February 1951 and died while a prisoner on 19 May 1951. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

Mehmen was awarded the Purple Heart, the Prisoner of War Medal, 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.