Answer:
Excitement, Purpose, Proud and maybe even (platonic) Love,
Step-by-step explanation:
Excitement: The troops would feel excitement before going out from the trenches to the battlefield, as, although it would be scary, the adrenaline would make them feel ready and extremely brave- which is always a good thing to feel.
Purpose: They would feel as though they have completed their purpose in the world, as they are protecting their friends, family, town, country and everyone else they are fighting for. This links onto the next emotion, which is feeling proud.
Proud: They would feel proud, because, of course, they are fighting in a big, important war, which they knew would make big history. They are most likely being the bravest they have ever been. They had to leave their homes and loved ones in order to protect them from the opposing countries, and this would make them feel a rush of disbelief, that they are brave enough to fight in such a deadly way, putting their life at risk for others.
Platonic Love: By this, I mean that they will have made good friends during the War, and they would feel a need to protect them, maybe. So, this can cause a positive emotion inside, much like when you see a friend who has helped and supported you through a lot, or just someone who you have had some good times with- in the soldier's case, to distract them form the deadly war happening. It gives them a feel that they should keep going, so that they can return the help and kindness back, or it can help distract the soldiers from the feeling of wanting to stop.
Hope this made sense!