The term for them (at least in the US) is AWOL - Absented Without Leave. A general term for those who've done such is deserter. Those of us who've known others who've done that while we went over and put ourselves in harm's way have a series of much more colourful names for them, but not a single one wouldn't violate this site's rules if I were to post it.
Chat with our AI personalities
Sometimes, people call the soldiers who keep watch for enemies Sentries or lookouts.
Discribe any one famous soldier/officer?
Soldier hired by the army of another country or by a private army, or a Soldier that will fight for you for pay enough.
A Spanish Soldier
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