There was a special word for Confederates who joined the US Army
Being a POW was not a great way to spend your enlistment in the Civil War, no matter which side you fought on. Depending on which POW camp you ended up locked into, your chances of survival were only slightly better. And if you did die, you probably died of some terrible disease.
So it makes a little sense why some Confederate troops had no problem turning around and joining the U.S. Army. They were called "Galvanized Yankees."
By 1863, Union lines were becoming stricken by desertions. Coupled with the death rate and the number of wounded and missing men, the U.S. Army in 1863 needed a solution for this coming manpower shortage in a hurry. But with draft riots already happening and enlistments drying up, where could the Union Army find a source of able-bodied men who could fight but were just sitting around, waiting? In the POW camps. And it wasn't just the Army fighting the Civil War who needed the help. Troops fighting Indian bands in the West needed augmentees as well.
So the Union formed the 1st Volunteer Infantry Regiment; former Confederate soldiers who had been captured, taken the oath of loyalty to the United States, and enlisted in the U.S. Army. It sure beat dying of dysentery or exposure at Camp Douglas.
Starting in 1863, the former Confederates stared down the Sioux tribe in Missouri while the war back home raged on. But they weren't the only ones who were needed. Ultimately four regiments of Confederate volunteers were formed for the Union. When the Confederates heard of this, they dubbed the POWs who took the deal "Galvanized Yankees," covering themselves and their deeds in the blue of the Union, the way a metal object is galvanized with a coating of zinc.
For most Southern troops, the choice wasn't all that hard – and it wasn't just about the conditions in POW camps. Many average Southern men weren't too keen on the strict Confederate class distinctions in the South, where poor whites were little more regarded than slaves. Add on the desire for the war to end, and the terrible conditions for Confederate troops, and the choice becomes more and more clear.
The Galvanized Yankees were sent to the American Plains, the Dakotas, Minnesota, and Missouri. The winters were not kind to the Southerners, who suffered from frostbite, scurvy, and other forms of malnutrition. To make matters worse, on top of enduring temperatures as cold a minus 29 degrees, the Lakota suddenly attacked on Nov. 27, 1863. The natives killed and wounded the new Army members throughout the winter and into the Spring of 1864. They would be able to hold out until the war's end, however.
In 1865, the men had held their soldiers' discipline, followed orders, and remained true to their oaths. Even after constant Indian attacks, brutal winters, and poor food, the Galvanized Yankees stayed at their posts. After two years, however, they were at their wits' end. The war was over, and so was their enlistment. They demanded to be mustered out. Two years after arriving in the Missouri region, they finally were.