Seventy-five years later, the world still marvels at the audacity and epic scope of D-Day. Some 160,000 Allied troops landed along a 50-mile stretch of heavily fortified French coastline, surprising and ultimately overrunning Nazi troops on the beaches of Normandy.

Epic, too, were the logistics, the carefully planned buildup and transport of materials and men necessary to carry out what Dwight Eisenhower called “a great crusade.” Military historian Christopher Johnson of the U.S. Army Command and General Staff College examines that overlooked phase of the June 6, 1944, invasion. Creative leaders used both wits and know-how to eventually pour a million troops, supported by more than half a million tons of supplies and 171,000 tanks, trucks, and other vehicles, into Normandy over a span of 30 days.