Private First Class Lanahan was a member of the 2nd Platoon, Company H, 3rd Battalion, 1st Marines, 1st Marine Division. He was Killed in Action while fighting the enemy at Hill 902 in Korea on 24 April 1951.

Lanahan 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.