Among the many key moments in World War II, few inspired more Allied cheers than Britain’s gallant resistance to the German bombings of its homeland that began in the autumn of 1940. With their backs to the wall, as the story goes, the British people staved off a Nazi invasion and thereby perhaps saved Western civilization. Here the distinguished historian William L. O’Neill challenges the commonly held view of the Battle of Britain as a victory against overwhelming odds. While the British defense of its island was certainly significant in the course of the war, Mr. O’Neill argues that it should not have been unexpected. The British, he writes, were well positioned to repel their foes. Here is his astute evaluation of these crucial events.