The carrying out of strategical combinations on a scale or of a character which would formerly have been impracticable.
Employment of railways for tactical purposes during the progress of a war, including therein (a) movement of troops from one part of the theatre of war to another, whether with a view to effecting big changes of front or otherwise; (b) employment of the same Army Corps on different fronts in succession, their transfer being effected in the briefest possible interval of time; (c) the rapid bringing up of reinforcements at a critical moment to some position exposed to overpowering attack which might otherwise be lost; (d) surprise attacks on the enemy; (e) the throwing of great masses of troops on distant points; (f) strengthening weak places in the fighting line; (g) strengthening threatened forts by means of troops, guns, munitions or supplies; (h) relief of invested fortresses, and (i) retirement by rail—when circumstances permit—of troops after defeat.
Control of a line of rail communication between the base and the strategic centre of operations, facilitating the enormous amount of transport in both directions which must be kept up in the rear of the army, and for which the elements of speed, safety and regularity may be of vital importance.
The possibility, thanks to railways, of regarding the whole interior of the national territory as a base for the supply of requirements at the front, dependence having no longer to be placed on a base established in one particular district with its restricted range of possible supplies and its collection of magazines, stores, workshops, transport parks, etc., protected by fortresses, entrenched camps, or other means of defence.
The establishment of supplementary, sectional or advanced bases along the line of communication, with railway services so arranged that supplies can be dispatched daily in such regulated quantities, and to such points, as will serve the immediate needs of the army in the field, without risk either of shortage or of excess.
Avoidance, under these conditions, of congestion of the railway lines in the immediate rear of the army by trains or loaded wagons containing a redundancy of supplies which (a) cannot be unloaded, (b) restrict the use of the lines for other purposes, and (c) might have to be abandoned to the enemy in the event of a sudden retreat.
Material benefits from the substitution of rail for road transport of food, etc., by reason of (a) greater speed and regularity; (b) less risk of deterioration from exposure to weather, and other causes; (c) decreased cost of transport as compared with earlier conditions involving the employment of a greater number of drivers, escort, guards, horses and road vehicles; and (d) the arrival at destination of the full quantities dispatched, the need for the consumption of an appreciable proportion en route by men and animals in a convoying wagon train, carrying supplies for long distances by road, being non-existent.
Reduction in the need for field ovens and other paraphernalia of the army cook, since much of the food required—bread, for example—can be prepared in cities or elsewhere at a distant base and forwarded regularly by rail.
Freedom, more or less complete, from the once prevalent obligation on the part of an advancing army that it should "live upon the country"—a condition which the enormous increase in the size of armies to-day would render impossible of fulfilment, even assuming that the people of the country invaded had not withdrawn live stock, vehicles and food supplies on their retirement before the invader.