Megiddo's Ridge — S. Fowler Wright

In 1938 the Nazis launch a sudden attack on Czechoslovakia, which they quickly subdue, and also on England, which proves to be a much harder morsel to digest. As the allies from the West gather their forces in Palestine for a final climactic battle at Megiddo's Ridge, British spy Richard Steele, who has infiltrated the highest levels of the German command, uncovers a great secret. But revealing it could cost him his position--and his life! The third book in an Alternate History of World War II.