Second Lieutenant Jarnagin was a member of the 3rd Battalion, 1st Marines, 1st Marine Division. He was Killed in Action while fighting the enemy near Youngdong-po on the outskirts of Seoul, South Korea on 21 September 1950.

Jarnagin 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.