What do you call a soldier who runs away?

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.