The best engineering and tactical brains of the German Army went to its planning; and both officers and men believed it to be impregnable.

The whole vast system was from four miles to seven miles deep, one interlocked and inter-communicating system of trenches, gun emplacements, machine-gun positions, fortified villages, and the rest, running from north-west to south-east across France, behind the German lines.

In front of the British forces, writes an officer of the First Army, before the capture of the Drocourt-Queant portion of the line, ran "line upon line, mile upon mile, of defences such as had never before been imagined; system after complicated system of trenches, protected with machine-gun positions, with trench mortars, manned by a highly-trained infantry, and by machine-gunners unsurpassed for skill and courage.
The whole was supported by artillery of all calibres.

The defences were the result of long-trained thought and of huge work.

They had been there unbroken for years; and they had been constantly improved and further organised." And the great canals--the Canal du Nord and the Scheldt Canal, but especially the latter, were worked into the system with great skill, and strongly fortified.