A Boy at War by Harry Mazer
Boys who read this book go right on to the next two in the series, A Boy No More and Heros Don't Run. They love them. Being that they are about a young boy first at Pearl Harbor than in the war, they are filled with action. It doesn't hurt that they are short books too - makes them appear less intimidating. Give them a chance - I don't think you'll regret it.
Over the next few days, Adam searches for answers -- about his friends, the war, and especially, his father. But Adam soon learns sometimes there are no answers.