"Blackout," a 2010 time-travel novel by Connie Willis, may be classified as science fiction, but because most of the story takes place during World War II, it is primarily a historical novel, and a very good one at that.
In the 2060s, historians study the past by going back in time and actually witnessing history firsthand. Three young historians are sent on separate missions to England during the early stages of the war. Mike goes back in time to learn more about the British rescue at Dunkirk and, without meaning to, becomes an active participant. Eileen must study the evacuation of children from London and gets stuck tending two impossible kids. Polly takes a job as a shopgirl in a department story to observe how Londoners react to the Blitz and somehow becomes cast in a play. Coming from the future, Polly knows where all the German bombs are going to strike, so she should be able to stay out of danger. That is, if she returns to her own time on schedule.
Each historian's assignment is intended to be short-term. If they don't return as scheduled, someone is supposed to come looking for them. Once they get to 1940, however, time travel doesn't quite work the way it is supposed to, and their routes back to the future are blocked. Mike, in particular because of his actions at Dunkirk, fears the Germans could actually win the war, and that it will be his fault.
By the end of the novel, all three historians have found one another, compared notes and realized the seriousness of their situation. To find out what happens next, one must read the sequel, "All Clear."
Connie Willis writes as if she had traveled back to wartime England herself. She gives her readers a feel for the time and place more vivid than almost any history book could provide, even one written by time-travelers.