It is evident also from the dispatch that Sir Douglas was quite aware, not only of the military, but of the political risk.

"The political effects of an unsuccessful attack upon a position so well known as the Hindenburg line would be large, and would go far to revive the declining _morale_, not only of the German Army, but of the German people." This aspect of the matter must, of course, have been terribly present to the mind of the British War Cabinet.
Moreover, the British Armies had been fighting continuously for nearly two months, and their losses, though small in proportion to what had been gained and to the prisoners taken, were still considerable.
Nevertheless, with all these considerations in mind, "_I decided_," says General Haig, "_to proceed with the attack_."[6] [6] The italics are mine.
There lie before me a Memorandum, by an officer of the General Staff, on the Hindenburg line, drawn up about a month after the capture of the main section of it, and also a German report, made by a German officer in the spring of 1917.

The great fortified system, as it subsequently became, was then incomplete.

It was begun late in 1916, when, after the battle of the Somme, the German High Command had determined on the retreat which was carried out in February and March of the following year.

It was dug by Russian prisoners, and the forced labour of French and Belgian peasants.