The usefulness of railways in war is limited by the following considerations, among others:—
Railways are "inferior to ships in power of simultaneously transporting heavy loads" (Von der Goltz). For this reason an overland route to India could never compete, in respect to military transport, with the sea route via the Suez Canal. Such overland route, also, passing through foreign countries, would be especially liable to attack and interruption. Where, however, the overland route goes entirely through national territory (as in the case of the Trans-Siberian Railway), and when the questions of time and safety, in regard to an alternative sea route, suggest possible disadvantages, railways will be preferred to ships in spite of the said inferiority.
Railways are inferior to roads in so far as, like rivers and canals, they are on fixed spots. Troops depending on them are thus able to move only in the direction in which lines have been or can quickly be laid, whereas if they went by road they might have a greater choice of alternative routes.
For these reasons the choice of the zone of concentration or of the "decisive points" may depend less to-day on political, military or geographical reasons (as in the Napoleonic wars) than on the direction, extent and capacity of the available railways.
Great masses of troops can be entrained only at stations where facilities for their so doing have been prepared in advance. The provision of these facilities is even more necessary in the case of Cavalry or Artillery than in that of Infantry. Hence the movement of considerable bodies of troops may be restricted to certain lines, and their entrainment or detrainment even to certain large stations. In the case of road marching these restrictions would not apply.
Vehicles specially constructed for the purpose can alone be used on railways. Any deficiency in their supply must needs cause delay.
During the time the troops are travelling by railway their power of resisting attack is much more restricted than it would be if they were marching by road, they can do little or nothing to protect the railway lines, while if the enemy can only get to the railway he may be in a position to prevent the train from continuing its journey, and take the troops in it at a disadvantage.
For these reasons, among others, troop movements by rail at the theatre of war, and especially in the enemy's country, are attended by a degree of risk which may render it desirable to abandon the use of the railway for the time being.
Railways are especially liable to destruction by the enemy, and, although the arrangements made in advance may permit of speedy repairs or reconstruction, the interruption of traffic for even a day or half a day may be a matter of grave importance during the concentration of the army or at some critical moment.
Destructions of line carried out by a retreating force, in order to delay pursuit by the enemy, will be to the disadvantage of that force when, after having driven back the enemy, it would itself make use of the line it had rendered unserviceable.