|If I understand your question correctly, I think it is next to impossible to answer without clarification. If you mean how many soldiers joined in 1861 and fought to 1865, does that discounts any soldiers that joined in 1862, 63, etc? You would have to drop soldiers who served their enlistments and were mustered out before the end of the war, but would you add back in soldiers who joined another unit. How would you count soldiers who were wounded or taken ill seriously enough to require several months or even years of convalescence before returning to their units? But, on the whole, I think you could get a very rough guess by looking at of the casualty returns of a few units who served though the entire war, though this is problematic because both Federal and Confederate units were replenished by new recruits throughout the war. Also, you would get a large discrepancy between line infantry, artillery and cavalry units and the rear echelon units. I'm afraid this may be a rather long winded way of saying that I think the question is impossible to answer with any degree of accuracy.