Generaloberst Wilhelm Ritter von Leeb, German army group commander in both the Polish and Western campaigns, was one of the world’s foremost authorities on defensive warfare. In 1936 he wrote an article and later a book on the subject (Die Abwehr). ‘Operative defence’, he wrote, ‘must meet the threat of offensive by using the same weapons and the same means.’ It echoed what Colonel de Gaulle had already written in his book, but the French Army would not believe it.

— Blitzkrieg by Len Deighton (Page 210)