The Bridges At Toko-Ri: by James A. Michener.

War is hard enough for people to go through, without having to explain to one's partner why one is not attentive and loving, which is a hazard when one cannot say much about the mission or its dangers, for various reasons. Or when - as it happened with Korean war - the rest of the world is at peace and it is hard to explain to everyone you know that there is still a war somewhere that must be attended to. And then there is the difficulty of the mission itself, which one may or may not succeed and return alive from, since the bridges at Toko Ri must be taken and they are situated at an extremely difficult place.