Galvanized Yankees was a term from the American Civil War denoting former Confederate prisoners of war who swore allegiance to the United States and joined the Union Army. Approximately 5,600 former Confederate soldiers enlisted in the "United States Volunteers", organized into six regiments of infantry between January 1864 and November 1866. Of those, more than 250 had begun their service as Union soldiers, were captured in battle, then enlisted in prison to join a regiment of the Confederate States Army. They surrendered to Union forces in December 1864 and were held by the United States as deserters, but were saved from prosecution by being enlisted in the 5th and 6th U.S. Volunteers. An additional 800 former Confederates served in volunteer regiments raised by the states, forming ten companies. Four of those companies saw combat in the Western Theater against the Confederate Army, two served on the western frontier, and one became an independent company of U.S. Volunteers, serving in Minnesota.
The term "galvanized" has also been applied to former Union soldiers enlisting in the Confederate Army, including the use of "galvanized Yankees" to designate them. At least 1,600 former Union prisoners of war enlisted in Confederate service in late 1864 and early 1865, most of them recent German or Irish immigrants who had been drafted into Union regiments. The practice of recruiting from prisoners of war began in 1862 at Camp Douglas at Chicago, Illinois, with attempts to enlist Confederate prisoners who expressed reluctance to exchange following their capture at Fort Donelson. Some 228 prisoners of mostly Irish extraction were enlisted by Col. James A. Mulligan before the War Department banned further recruitment March 15. The ban continued until 1863, except for a few enlistments of foreign-born Confederates into largely ethnic regiments.
Three factors led to a resurrection of the concept: an outbreak of the American Indian Wars by tribes in Minnesota and on the Great Plains; the disinclination of paroled but not exchanged Federal troops to be used to fight them; and protests of the Confederate government that any use of paroled troops in Indian warfare was a violation of the Dix-Hill prisoner of war cartel. Gen. Gilman Marston, commandant of the huge prisoner of war camp at Point Lookout, Maryland, recommended that Confederate prisoners be enlisted in the U.S. Navy, which Secretary of War Edwin Stanton approved December 21. General Benjamin Butler's jurisdiction included Point Lookout, and he advised Stanton that more prisoners could be recruited for the Army than the Navy. The matter was then referred to President Lincoln, who gave verbal authorization on January 2, 1864, and formal authorization on March 5 to raise the 1st United States Volunteer Infantry for three years' service without restrictions as to use.