Was watching a documentary. An allied infantry survivor in WW1 recalled that when he saw his German enemy, he recalled the commandment that "thou shalt not kill," and instead of killing the German he shot him in the legs.
Did this occur often?
Don't have a direct answer but there were conscientious objectors. Mormons, Amish, etc. I think some didn't have to fight as religion was taken a lot more serious back then. And at that time most of the soldiers would have had religion of one faith or the other. The old movie Sargent York partly deals with this. Don't know how true.