John Perkins Reynolds, a member of the "Salem Zouaves" (Company I, Eighth Massachusetts Infantry), left behind a unique record of one company's service during the early months of the Civil War. His diary documents his company's hourly activities each day, forming a rare chronicle of a Union "three-month" unit. Reynolds was a talented and perceptive writer, and he meticulously recorded details about many events.

The early mobilization of Union volunteers, Northern and border state support for the war effort, the movement of troops to defend Washington, D.C., from an expected Confederate attack, the "rescue" of the U.S.S. Constitution, raids on secessionist farms in Maryland, and life in the troubled city of Baltimore are just a few of the topics highlighted in his diary.

Reynolds included many insightful details about soldier life and material culture during the period. Army discipline, religious practices, soldier-civilian encounters, training, rations, humor and numerous other aspects of the soldier's existence were deemed noteworthy.