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.
One of the earliest and most obvious criticisms advanced against the use of railways in war was based on the vulnerability of the iron road. The destruction of a bridge, the tearing up of a few rails or the blocking of a tunnel would, it was argued, suffice to cause an interruption in the transport of troops or supplies which might be of serious consequence to the combatants prejudiced thereby, though of corresponding advantage to the other side. By means of such interruption the concentration of troops on the frontier might be delayed; an army might be divided into two or more parts, and exposed to the risk of defeat in detail; the arrival of reinforcements urgently wanted to meet a critical situation might be prevented until it was too late for them to afford the desired relief; a force advancing into an enemy's country might have its rail connection severed and be left to starve or to surrender at discretion; invaders would find that the force they were driving before them had taken the precaution to destroy their own railways as they retreated; or, alternatively, lines of railway constructed to the frontier, and depended upon to facilitate invasion of neighbouring territory, might--unless destroyed--be of material service to the enemy, should the latter become the invaders instead of the invaded.