These details may convey some idea of all that was involved in the utilisation of rail-power in the American Civil War under such development of railway construction as had then been brought about. Great, however, as was the outlay, the forethought, the energy, the patience and the watchfulness spoken of by McCallum, the results were no less valuable from the point of view of the Federals, who could hardly have hoped to achieve the aim they set before themselves—that of saving the Union—but for the material advantages they derived from the use of the railways for the purposes of the campaign.
Some of the achievements accomplished in the movement of troops from one part of the theatre of war to another would have been creditable even in the most favourable of circumstances; but they were especially so in view alike of the physical conditions of many of the lines, the inadequate supply of rolling stock, and the risks and difficulties to be met or overcome.
One of these achievements, carried out in September, 1863, is thus narrated in an article on "Recollections of Secretary Stanton," published in the Century Magazine for March, 1887:—
The defeat of Rosecrans, at Chickamauga, was believed at Washington to imperil East Tennessee, and the Secretary [of War] was urged to send a strong reinforcement there from the Army of the Potomac. General Halleck (General-in-Chief of the Army of the United States) contended that it was impossible to get an effective reinforcement there in time; and the President, after hearing both sides, accepted the judgment of Halleck. Mr. Stanton put off the decision till evening, when he and Halleck were to be ready with details to support their conclusions. The Secretary then sent for Colonel McCallum, who was neither a lawyer nor a strategist, but a master of railway science. He showed McCallum how many officers, men, horses, and pieces of artillery, and how much baggage, it was proposed to move from the Rapidan to the Tennessee, and asked him to name the shortest time he would undertake to do it in if his life depended on it. McCallum made some rapid calculations, jotted down some projects connected with the move, and named a time within that which Halleck had admitted would be soon enough if it were only possible; this time being conditioned on his being able to control everything that he could reach. The Secretary was delighted, told him that he would make him a Brigadier-General the day that the last train was safely unloaded; put him on his mettle by telling him of Halleck's assertion that the thing was beyond human power; told him to go and work out final calculations and projects and to begin preliminary measures, using his name and authority everywhere; and finally instructed him what to do and say when he should send for him by and by to come over to the department. When the conference was resumed and McCallum was introduced, his apparently spontaneous demonstration of how easily and surely the impossible thing could be done convinced the two sceptics, and the movement was ordered, and made, and figures now in military science as a grand piece of strategy.
The feat thus accomplished was that of conveying by rail 23,000 men, together with artillery, road vehicles, etc., a distance of about 1,200 miles in seven days. It was estimated that if the troops had had to march this distance, with all their impedimenta, along such roads as were then available, the journey would have taken them three months. By doing it in one week they saved the situation in East Tennessee, and they gave an especially convincing proof of the success with which "a grand piece of strategy" could be carried out through the employment of rail transport.
In December, 1864, General Schofield's corps of 15,000 men, after fighting at Nashville in the midst of ice and snow, was, on the conclusion of the campaign in the west, transferred from the valley of the Tennessee to the banks of the Potomac, moving by river and rail down the Tennessee, up the Ohio and across the snow-covered Alleghanies, a distance of 1,400 miles, accomplished in the short space of eleven days. In 1865 the moving of the Fourth Army Corps of the Federals from Carter's Station, East Tennessee, to Nashville, a distance of 373 miles, involved the employment of 1,498 cars.
What, in effect, the Civil War in America did in furthering the development of the rail-power principle in warfare was to show that, by the use of railways, (1) the fighting power of armies is increased; (2) strategical advantages unattainable but for the early arrival of reinforcements at threatened points may be assured; and (3) expeditions may be undertaken at distances from the base of supplies which would be prohibitive but for the control of lines of railway communication; though as against these advantages were to be put those considerations which also arose as to destruction and restoration, and as to the control of railways in their operation for military purposes.