The spring and summer of 1940 witnessed the resounding defeats of the French army and British Expeditionary Force at the hands of modernized German troops, designed to take advantage of the latest advances in technology. These included mobile vehicles and tanks used in formation to blast through enemy lines, as well as combined ground and air tactics. The evacuation of the British from Dunkirk and the final defeat of their French allies in June 1940 left only a thin line of English fighter planes between that island nation and total defeat. Meanwhile, leaders of the United States Army,...