The outbreak of the Civil War caught the U.S. Army unprepared. President Lincoln called up seventy-five thousand volunteers for military service, a call answered by boys and young men throughout the North. Many were farmers and small-town dwellers for whom military life represented an escape from a dull routine. The volunteers gathered in companies of one hundred, elected their leaders from among themselves, and drilled on courthouse lawns and open fields from Minnesota to Maine.

At first, army service meant no more than endless drilling and marching. As the Union generals dithered, bored volunteers sought what diversions they could in the huge encampments around Washington. Gambling, target shooting, carousing, and writing letters home held more interest for the volunteers than the movements of the Confederates. The war, they thought, would go quickly and easily, and might pass most men by completely...