When the United States entered World War I, the medical profession was far better prepared than the military, and the first assistance of any sort that the United States was able to send was medical. During the first year of the war, 1917, we were unable to give much in the way of effective military aid, yet we were able to send thousands of physicians, nurses, and orderlies to render services in the hospitals at the front. It was not until the spring of 1918 that American combat forces began to appear in France in any substantial numbers.
Thus, two physicians had the dubious honor of becoming the first American officers killed or wounded in the war. The incident occurred when the Harvard Base Hospital No. 5 was bombed. The first American officer to be killed was William Fitzsimons, MD, after whom the Fitzsimons General Hospital in Denver is named.
Smith R. The First American Officer Wounded in World War I. JAMA. 1982;247(12):1743. doi:10.1001/jama.1982.03320370057034