On 7 August 1918 the President of the French Republic raised General Ferdinand Foch to the dignity of Marshal of France. Foch had reached the pinnacle of his military career. Less than five months earlier, on 26 March 1918, he had been chosen by unanimous consent of the British and French military and political leaders to be Generalissimo of the Allied armies on the Western Front. To undertake the terrible responsibility thrust on him Foch would be required to draw on all he had learned as a soldier in the prewar period and to reflect on his performance as a commander since August 1914. This book is a study of Foch’s command in the positions that he occupied during the war; its aim is to examine how Foch’s ideas evolved as he moved along the path that led to the supreme command. As Foch himself wrote: one does what one can to apply what one knows.