Major Hernan was the pilot of an F4U-5N Corsair night fighter with the Marine Night Fighter Squadron 513, Marine Air Group 12, 1st Marine Air Wing. On 19 July 1951, while on a combat mission northwest of Masan-ni, Korea, his aircraft crashed and burned.

Hernan 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.