He reported for active duty with the United States Marine Corps on 29 April 1942 at New River, North Carolina.

On 14 September 1942 Private First Class Herndon was serving with the 1st Marine Division during action against Japanese forces on Guadalcanal in the Solomon Islands.

While engaged in a hazardous reconnaissance patrol on the southern slope of a hill, Herndon was mortally wounded.

With Japanese forces advancing rapidly on his position and realizing that he had no chance to survive, he asked that he be left with a weapon to cover the withdrawal of his patrol to the top of the hill.

During the assault phase of the Okinawa operation, she assisted in maintaining an outer antisubmarine screen that extended completely around the Hagushi Beach transport area and the seaplane and logistics anchorage at Kerama Retto.