After graduating from Baker High School, Johnston joined the Army from his birth city of Columbus, Georgia in 1968.

On that day, in Tay Ninh Province, Republic of Vietnam, during Operation Toan Thang III Johnston smothered the blasts of three enemy-thrown explosives with his body, sacrificing his life to protect those around him.

Specialist Johnston's official Medal of Honor citation reads: For conspicuous gallantry and intrepidity in action at the risk of his life above and beyond the call of duty.

Sensing the danger to his comrades, Sp4 Johnston, with complete disregard for his safety, hurled himself onto the explosive charges, smothering the detonations with his body and shielding his fellow soldiers from the blast.

Sp4 Johnston's concern for his fellow men at the cost of his life were in the highest traditions of the military service and reflect great credit upon himself, his unit, and the U.S. Army.