Not entirely sure how to phrase this question...
Would he be on the battlefield, and what would he be doing?
More importantly: what kind of stuff would he be saying on the battlefield? What sounds would he associate with it? And what phrases would he be likely to yell out at someone?
I don't need him to say (or hear) anything specific. I just need a whole bunch of noises and sentences that would be associated with the army in world war one, so that someone hearing them might be able to recognise where they're from.
Actually, stuff said in training, or in the barracks (are they barracks?) would be just as helpful.
...hopefully that makes some kind of sense.