Difficulties arose, also, on the side of the Germans in operating the 2,500 miles of French railway lines of which they took possession. There was, in the first place, a deficiency both of locomotives and of rolling stock. So far as circumstances would permit, the French, as they retreated, either took their railway rolling stock with them or destroyed it, in order that it should not be used by the enemy. Attempts were made to meet the difficulty by obtaining constant reinforcements of engines and wagons from Germany; but even then the organisation for controlling the use of rolling stock, among other transport details, was still so defective that commanders who wanted to ensure the movement of their own troops by rail did not hesitate to take possession of engines and carriages set aside for the regular services of the line. There were, in fact, occasions when, for this reason, the regular services had to be stopped altogether. In the next place troubles with the _personnel_ were no less acute than those with the _matériel_. In proportion as the Germans advanced towards Paris the bulk of the French population retired, while threats and offers of liberal pay alike failed to secure from those who remained assistance either in repairing or in operating the lines of which the invaders had taken possession. In these circumstances not only engines, carriages and wagons, but no fewer than 3,500 railwaymen--in addition to the German Railway Troops already in France--had to be brought from Germany. Yet even the resort to this expedient started a fresh lot of troubles. The railwaymen so imported had been in the service of different German railway companies whose equipment and methods of operation varied considerably; so that when the men were required to work together--and that, also, on the lines of a foreign country, with the accompaniment of much laxity in discipline as well as of much mutual misunderstanding--a vast amount of friction arose. All these experiences emphasised and strengthened the conclusion arrived at even before the campaign of 1870-71--that the real efficiency of Railway Troops can only be obtained by organising them in time of peace in readiness for times of war. Such conclusion being now beyond all possible dispute, action was taken by Prussia with characteristic promptness.