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March 19 marks the fifth anniversary of the U.S. invasion of Iraq. The American death toll—nearly 4,000 soldiers in Iraq and almost 500 in Afghanistan—is well known. Much less attention has been paid to the enormous number of troops who have survived and returned home with serious injuries. Here, the numbers are truly staggering. More than 70,000 have been wounded in combat, injured in accidents, or airlifted out of the region for emergency medical care. More than a third of the 750,000 troops discharged from the military so far have required treatment at medical facilities, including at least 100,000 with mental health conditions and 52,000 with post-traumatic stress disorder. According to a recent U.S. Army estimate, as many as 20 percent of returning soldiers have suffered mild brain injuries, such as concussions. More than 20,000 troops have survived amputations, severe burns, or head, spinal, and other serious injuries.

These numbers are largely due to the extraordinary advances in battlefield medicine in recent years. Far more soldiers are surviving even grievous injuries than in previous conflicts. The ratio of wounded in combat to killed in Iraq is 7 to 1; in Vietnam, it was 2.6 to 1, and in World War II, 2 to 1. If all injuries are included, such as those from road accidents or debilitating illnesses, Iraq has produced 15 wounded for every single fatality. This higher survival rate is, of course, welcome news, but it leaves the United States with a legacy of providing medical care and paying disability benefits to an enormous number of veterans and their dependents for many decades to...