The President of the United States of America takes pride in presenting the Navy Cross (Posthumously) to Hospitalman Second Class William Ivan Mercer (NSN: B-980863), United States Navy, for extraordinary heroism on 15 June 1968 while serving as Senior Corpsman of Company M, Third Battalion, Fourth Marines, THIRD Marine Division (Reinforced), Fleet Marine Force, in connection with operations against enemy aggressor forces in the Republic of Vietnam. While conducting a sector of the battalion defense perimeter, Company M became heavily engaged with a large North Vietnamese Army force near Khe Sanh, and sustained numerous casualties. Reacting instantly, Petty Officer Mercer began assisting the injured Marines to a covered area for treatment, ensuring their further movement to the battalion landing zone for medical evacuation. On many occasions, he unhesitatingly moved to the points of heaviest contact and maneuvered about the fire-swept terrain to treat men who lay wounded in their fighting holes or the perimeter. When a platoon was assigned the mission of searching the area forward of friendly positions, Petty Officer Mercer voluntarily accompanied this unit and subsequently came under accurate enemy sniper fire. Upon observing a seriously wounded Marine, he fearlessly left his covered position and maneuvered across the hazardous area to the side of his injured comrade. Completely disregarding his own safety, Petty Officer Mercer shielded the man with his own body as he administered first aid, and then carried him to a position of relative safety. Alertly observing another casualty lying in an area dangerously exposed to the intense fire, Petty Officer Mercer rushed to his aid, and again selflessly used his own body to protect the Marine from the hostile fire impacting around them. While administering medical treatment to his comrade, Petty Officer Mercer was fatally wounded by the North Vietnamese fire. By his daring initiative, exceptional valor, and inspiring actions, he was directly responsible for saving the lives of several wounded men. His selfless devotion to duty was in keeping with the highest traditions of the United States Naval Service.