GALVANIZED YANKEES were Confederate soldiers imprisoned during the Civil War but granted their freedom in exchange for an oath of allegiance to the United States and enlistment in the Union army. About six thousand former Confederates enrolled in six regiments of U.S. volunteers during 1864 and 1865, and a few hundred others joined state volunteer units. Samuel Bowles coined the term in the Springfield (Mass.) Republican on 24 May 1865.
At General Ulysses S. Grant's insistence, the six regiments of Galvanized Yankees served in the West, manning frontier forts, guarding stagecoach routes, escorting supply trains, and rebuilding hundreds of miles of telegraph lines destroyed by Indians, thus avoiding service against former comrades-in-arms.
Brown, Dee. The Galvanized Yankees. Urbana: University of Illinois Press, 1963.