But Ludendorff's major plan, having failed in the first month of his offensive, could not be repeated in the second. Since April 30 there has been no French, British, Belgian, Portuguese, or American front in Flanders or Picardy--only the front of the Allies, with the troops of their several nations used wherever needed by the supreme commander, Foch. During the first month of the offensive two angles had been developed by Ludendorff: The first, the great one, in the south, from a base of sixty miles with a forty-mile perpendicular and its vertex near the Somme; the second in the north, from a base of twenty miles with a fifteen-mile perpendicular and its vertex on the edge of the Forest of Nieppe. Between these two angles the original front of Lens, from Bailleul north to Givenchy, still held, fifteen miles in length. There had been voluntary or forced changes made by the Allies east of Ypres and east of Arras. [Illustration: DIAGRAM OF CRITICAL SITUATION, MARCH 24, 1918, WHERE GENERAL FAYOLLE SAVED THE DAY BY THROWING HIS DIVISIONS INTO THE THIRTY-MILE GAP LEFT BY RETIREMENT OF BRITISH 5TH ARMY] The corollary in Flanders, unless it could be demonstrated, would be as great a failure as the main proposition in Picardy. And the still possible successful issue of the latter depended absolutely, as we shall see, on a complete demonstration of the former. Both have been so far handicapped by the augmenting mobility of the Allies, their growing numbers, their centralized command, and their successful insistence to control the air. Such was the situation in Flanders and Picardy which confronted Ludendorff at the dawn of the second month of the German offensive. The whole problem to be solved was just as apparent to the Allies as it was to him--to gain the barriers which threatened his angles of penetration, in order again to utilize his preponderant forces of men and guns on a broad front. To attempt to extend the vertices without broadening the sides would mean to court danger, even destruction, at their weakest points. His frontal attacks upon Ypres and Arras, respectively from the Passchendaele Ridge and against the Vimy Ridge, having failed, it became necessary to attempt to flank the Allies by the occupation of their defensive ridges. This explains his successful assaults upon Mont Kemmel, 325 feet high, and his desire to envelop Mont Rouge, 423 feet high, and his persistent attacks along the La Bassée Canal against the heights of Béthune, 141 feet, all preceded by diversions between the Somme and Avre, with concentrations at Villers-Bretonneux, Hangard, and elsewhere. [Illustration: PERSPECTIVE MAP SHOWING LOCATION OF OPPOSING FORCES IN PICARDY AND FLANDERS. THE BLACK ARROW LINE ON THE RIGHT SHOULD NOT BE MISTAKEN FOR THE OLD BATTLELINE, WHICH IS NOT INDICATED AT ALL. GENERAL SIXT VON ARNIM'S FORCE, EAST OF YPRES, WAS INADVERTENTLY OMITTED]