One of the greatest disadvantages of the American railways at the time of the Civil War lay in their differences of gauge. The various companies had built their lines with gauges chosen either to suit local conditions or according to the views of their own engineers, with little or no consideration for the running of through traffic on or from other lines. There were, in fact, at that time gauges of 6 ft., 5 ft. 6 in., 5 ft., 4 ft. 10 in., 4 ft. 9 in., 4 ft. 8½ in. (the standard English gauge), and various narrower gauges besides. These conditions prevailed until 1866, when the companies adopted a uniform gauge of 4 ft. 8½ in. During the Civil War the lack of uniformity was in full force, and military transport by rail was greatly complicated in consequence. More than one-half of the lines taken over and operated had a gauge of 5 ft., and the remainder had a gauge of 4 ft. 8½ in., except in the case of one short line, which was 5 ft. 6 in. As locomotives and rolling stock adapted to one gauge were unsuited to any other, the obligations falling upon the Director and General Manager of the Federal Military Railways included that of taking up the lines of certain companies which had adopted the 5 ft. gauge, and relaying them with the 4 ft. 8½ in. gauge, so that the same rolling stock could be used as on lines connecting with them. Incidentally, therefore, the Civil War in America taught the lesson that the actual value of rail-power as influencing warfare in one and the same country, or on one and the same continent, may vary materially according to whether there is uniformity or diversity of railway gauge. In certain instances the lines taken possession of were in so defective a condition that it was imperatively necessary to relay them, apart altogether from any question of gauge. When McCallum was appointed General Manager of Military Railways for the Division of the Mississippi, the main army was at Chattanooga, Tennessee, and its supplies were being received from Nashville, 151 miles distant, over the Nashville and Chattanooga Railroad. This was necessarily the main line of supply during the subsequent campaigns from Chattanooga towards Atlanta, and from Knoxville towards South-western Virginia; yet McCallum says of it, in the Final Report he presented to the Secretary of War in 1866:-- The track was laid originally in a very imperfect manner, with a light U-rail on wooden stringers which were badly decayed and caused almost daily accidents by spreading apart and letting the engines and cars drop through them. In still other instances, lines which, though begun, were not finished, had to be completed; in others new lines had to be constructed throughout, or extensive sidings provided; so that once more we see that it was not then simply a question of the Federal Government taking possession of and operating an existing complete and efficient system of railways.