“A solider in command must be told not to kill people; if he is order to do so, he should not carry it out. Nor should he take the oath. If he will not agree, he should be rejected. Anyone who has the power of the sword, or who is a civil magistrate wearing the purple, should desist, or he should be rejected. If a catechumen or a believer wishes to become a soldier they should be rejected, for they have despised God.”
Hippolytus, “On the Apostolic Tradition.” (SVS Press, 100). Mid 3rd century.