very difficult problem,
while the capture of Sailly-Saillisel, at that time some 3,000 yards to
the north of the French left, was in some respects even more difficult.
The line of the French advance was narrowed almost to a defile by the
extensive and strongly fortified Wood of St. Pierre Vaast on the one
side, and on the other by the Combles Valley, which, with the branches
running out from it and the slopes each side, is completely commanded,
as has been pointed out, by the heights bounding the valley on the east
and west.

[Sidenote: Close cooperation necessary on right.]

On my right flank, therefore, the progress of the French and British
forces was still interdependent, and the closest cooperation continued
to be necessary in order to gain the further ground required to enable
my centre to advance on a sufficiently wide front. To cope with such a
situation unity of command is usually essential, but in this case the
cordial good feeling between the allied armies, and the earnest desire
of each to assist the other, proved equally effective, and removed all
difficulties.

[Sidenote: Enemy defense on main ridge over Thiepval.]

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 b