For World War I, Americans mobilized a medical and public health effort unprecedented in its scale and scope. With only a small medical corps in the standing armed forces, the American Red Cross played a critical role in providing medical care to wounded and sick service members. Thousands of Americans, women and men, volunteered for the Red Cross, many of them staffing dozens of hospitals in Europe. In addition to treating those wounded by war, the medical services struggled to fight the worldwide influenza epidemic that broke out in 1918. The flu killed more than 30 million people around the world, including 675,000 Americans, more than were killed in the fighting of the Great War.