Frederick Knefler served in the Union Army in the U.S. Civil War, joining as a first lieutenant in May 1861. He served as a staff officer and as colonel of the 79th Indiana Infantry Regiment and an acting brigade commander. In 1866, he was nominated and confirmed for appointment to the grade of brevet brigadier general of volunteers, to rank from March 13, 1865.

The Battle of Pickett's Mill was fought in Paulding County, Georgia, between Union forces under Major General William Tecumseh Sherman and Confederate forces led by General Joseph E. Johnston during the Atlanta Campaign in the American Civil War. Sherman sent Brigadier General Thomas J. Wood's division, supported by other formations, to turn Johnston's right flank, but the Federals were repulsed with heavy casualties when they ran into tenacious Confederate opposition. Author Ambrose Bierce, an eyewitness, later wrote an account of the battle titled The Crime at Pickett's Mill.