About 391,000 US Marines served in the Vietnam War; almost 15,000 of them died. The jungle conditions made disease a problem. During Vietnam, almost 11,000 soldiers died of disease as opposed to 47,000 combat deaths. Advances in field medicine, antibiotics, and the use of helicopters to evacuate the wounded significantly cut down on deaths by illness as compared with earlier American wars. For example, in the US Civil War, the Union lost 140,000 men to bullets, but 224,000 to disease.