YEONGWOL COUNTY, South Korea — As the United States wages war on Iran , it is burning through stockpiles of advanced weapons and ammunition, including Tomahawk, Patriot and Precision Strike missiles. Replacing them will require a powerful metal, tungsten, whose production and refining is dominated by China — leading the U.S. to desperately search for it elsewhere. Tungsten is used in fighter jets, bunker buster bombs, armor-piercing rounds and missile systems, making it indispensable for