Longacre (Custer: The Making of a Young General) examines the career of the Union army general David McMurtrie Gregg (1833–1916), who served under better-known military leaders and never achieved extensive public notoriety and recognition. While the book’s title mentions Gregg’s important role during the third day of fighting at Gettysburg, most of the volume details his achievements before and after that key encounter. Gregg’s early career took him from his home in Pennsylvania, first to the military academy at West Point, then to the American West where he took part in the United States’ campaign to colonize the Washington Territory. There he learned the command of cavalry that, Longacre argues, served him well when he was called east after the outbreak of the Civil War. Promoted to the rank of brigadier and eventually major general, Gregg encountered both successes and controversies that this book says were typical of mid-level officers. Longacre speculates on but fails to conclusively determine the reason for Gregg’s mysterious retirement in the final months of the Civil War. This book sheds light on the career of an accomplished but largely unappreciated officer. VERDICT Longacre’s skill at military history makes for fascinating reading for those desiring to broaden their knowledge of the Union army’s officer corps.