Take, for instance, Sir Arthur Conan Doyle’s fifth volume.[99] It opens on a very _piano_ note. ‘The late winter and the early spring of 1918 saw the balance tilted against the British and their comrades in the West, through causes over which they had no control.... From November [1917] to March [1918] an endless succession of troop trains were bearing the divisions which had extended from the Baltic to the southern frontiers of Russia, in order to thicken the formidable array already marshalled across France.’ Or take the expert evidence of Major-General Sir Frederick Maurice[100]: ‘In Europe 1917 was a year of disappointment for the arms of the Allies.... From the beginning of November onward they [the Germans] were moving troops from the Russian to the French front as fast as their trains could carry them. It was calculated that the Germans would be able to increase their strength on the Western front between the beginning of November and the end of April by not less than a million and a half of men’: a very nasty calculation for the Allied Command, and for the two Governments behind it at home. Moreover, there was not much time. This was the key to the situation. Troops moving as fast as they could travel would reach their destination earlier than troops which were moving through a longer distance at a slower rate. ‘While it would be possible,’ wrote Sir Douglas Haig,[101] ‘for Germany to complete her new dispositions early in the new year, the forces which America could send to France before the season would permit active operations to be recommenced would not be large’: again, a very simple calculation, but it entailed serious consequences. The first was, that ‘it became necessary to change the policy governing the operations of the British Armies in France’[102]; or, rather, this was less the first consequence than the sum-total of the consequences, which involved in their train all kinds of major and minor changes. The policy governing the operations of the British Armies in France had to be changed. 1918 had to be adjusted to 1917; and, while the process of adjustment unmade, or, at least, disturbed, the whole basis of British dispositions, and robbed the seed-time of the harvest, it was by no means clear that the new course would be either satisfactory or complete. For the change from an offensive to a defensive policy, under the urgent threat of a German advance, was accompanied by (1) a reduction in the British fighting strength, (2) a deficiency in defensive training, and (3) an extension of the British front by over twenty-eight miles. Such, briefly, was the problem at the opening of December, 1917, while General Braithwaite’s gallant troops were still winning laurels in front of Cambrai, and public opinion in England was still uncertain whether the ‘break-through’ had come or not. As a fact, it was coming from the other side. It was coming with a weight of men and guns unequalled in the history of warfare. It