On my left flank the front of General Gough's army bent back from the main ridge near Mouquet Farm down a spur descending southwestward, and then crossed a broad valley to the Wonderwork, a strong point situated in the enemy's front-line system near the southern end of the spur on the higher slopes of which Thiepval stands. Opposite this part of our line we had still to carry the enemy's original defenses on the main ridge above Thiepval, and in the village itself, defenses which may fairly be described as being as nearly impregnable as nature, art, and the unstinted labor of nearly two years could make them. [Sidenote: British advance on Thiepval defenses.] [Sidenote: Positions might be rushed.] Our advance on Thiepval and on the defenses above it had been carried out up to this date, in accordance with my instructions given on July 3, 1916, by a slow and methodical progression, in which great skill and much patience and endurance had been displayed with entirely satisfactory results. General Gough's army had, in fact, acted most successfully in the required manner as a pivot to the remainder of the attack. The Thiepval defenses were known to be exceptionally strong, and as immediate possession of them was not necessary to the development of my plans after July 1, 1916, there had been no need to incur the heavy casualties to be expected in an attempt to rush them. The time was now approaching, although it had not yet arrived, when their capture would become necessary; but from the positions we had now reached and those which we expected shortly to obtain, I had no doubt that they could be rushed when required without undue loss. An important part of the remaining positions required for my assault on them was now won by a highly successful enterprise carried out on the evening of September 14, 1916, by which the Wonderwork was stormed. [Sidenote: Plan of combined attack.] [Sidenote: Main effort against Rancourt and Fregicourt.] The general plan of the combined allied attack which was opened on September 15 was to pivot on the high ground south of the Ancre and north of the Albert-Bapaume road, while the Fourth Army devoted its whole effort to the rearmost of the enemy's original systems of defense between Morval and Le Sars. Should our success in this direction warrant it I made arrangements to enable me to extend the left of the attack to embrace the villages of Martinpuich and Courcelette. As soon as our advance on this front had reached the Morval line, the time would have arrived to bring forward my left across the Thiepval Ridge. Meanwhile on my right our allies arranged to continue the line of advance in close co-operation with me from the Somme to the slopes above Combles, but directing their main effort northward against the villages of Rancourt and Fregicourt, so as to complete the isolation of Combles and open the way for their attack upon Sailly-Saillisel.