Although born in Frederick County, Maryland, where his family had lived for five generations, Detrick lived a portion of his childhood in Orange, Virginia, where his grandfather owned Montpelier, President James Madison’s former home. He graduated from the Rockefeller Institute and completed his medical internship at Bellevue Hospital, both in New York City. He was appointed a lieutenant in the Medical Reserve Corps, U.S. Army in April 1918. His first brief assignment was to the installation hospital at Camp Wadsworth, South Carolina, followed by a tour of duty with the 28th Aero Squadron, 3rd Pursuit Group in France. He supported the major American offensives at the battles of Saint-Mihiel and of &lt;a href="Meuse-Argonne%20Offensive"&gt;Meuse/Argonne&lt;/a&gt;. He was discharged at Camp Dix, New Jersey, in July 1919.