What's the situation here? What are they talking about? Remember, the prompt is just a jumping off point. Although there's only one soldier who is talking in the photo, the dialogue doesn't need to begin with him. All the men hold interest. Are you drawn to the smoker, the man with the goggles? The one taking notes? Or any of the others.
Again, think point of view. Each of the men holds different points of view. Who's will you choose?
Perhaps you want to start with a free-for-all where you don't follow one point of view. This is an interesting exercise. Just begin the conversation and see which man's point of view emerges as the strongest and most interesting. Then rewrite the dialogue using only his point of view.
Don't worry if you think you can't write dialogue! I've never worked with anyone who can't write dialogue, only with people who think they can't. It is amazing what you learn once you free the character to say everything he or she wants to say!