Only 13, which is less than a third of what Lincoln hanged at one time. They were also Hanged for Treason. But you didn't mention that. For some reason you characterized them as "P.O.W."s instead of traitors.
But the prisoners taken by Pickett’s men at New Berne had an additional twist to their story, for they were accused of switching sides — serving in the Confederate Army, then deserting and fighting for the Northern cause.
By that sort of logic the Union could have, and by rebel standards should have, hanged every Confederate soldier they captured for treason.