Before he left England Lord Roberts had determined on the line for the advance of the army which he had to command in person. Though in detail his scheme was somewhat modified afterwards, he began to prepare for the execution of it as soon as he had landed. For reasons which will be more fully recorded in his own words, he had decided to choose the route along the western line of railway, on which side alone a bridge over the Orange river was in his possession. In order to possess the freedom of movement essential to the execution of any sound schemes of war, he determined to make such arrangements as would enable him to cast himself loose from the railway and to march across the Free State eastward. His first idea was to strike the central railway as close as possible to Springfontein junction. He believed that the Boers would thus be compelled to evacuate their positions at Stormberg and Colesberg, and to abandon to him the Norval's Pont and Bethulie bridges over the river. The Commander-in-Chief was convinced, moreover, that this course, by menacing Bloemfontein, would oblige the enemy to relax his hold on the Modder river and Natal.[287] But, on the 27th January, increasing anxiety as to Kimberley led him to decide that the prompt relief of that town had become necessary. This involved, not a change of plan, but merely a modification of details. The initial march eastward was still to be carried out, but as soon as Cronje's flank had thus been effectively passed, a wheel northward would bring the British troops athwart the Boer line of communication, and, when the passage of the Modder was made, the way to Kimberley would be opened.[288] After relieving Kimberley the Field-Marshal's movements would depend on the situation, as it might then present itself, but should such a march appear possible, he determined to make straight for Bloemfontein.[289] The occupation of that capital would, he thought, make it easy to re-establish direct railway communication with Cape Colony through Norval's Pont and Bethulie. The considerations which guided Lord Roberts to the adoption of this plan, as finally formulated, were explained by him in detail nearly three years later to the War Commission in the following terms:[290]
"Before leaving England I had practically determined that the advance must be through the Orange Free State, but by one, not by three lines through Cape Colony, as was originally intended;[291] and the western line commended itself to me for the following reasons:
"1. It was on that line only that we had possession of a railway bridge over the Orange river:
"2. It was by that line only that Kimberley could be relieved in time, and had Kimberley fallen, Mafeking must have fallen also:
"3. It was by that line only I could deal with the Boer forces in detail, and defeat Cronje before he could be reinforced.
"Both the Norval's Pont and Bethulie bridges were in the hands of the enemy, and by the time I had forced them back into the Orange Free State, and had been able to repair either of these bridges (which I was certain would be destroyed, and which actually happened), and I had occupied Bloemfontein, I should have between me and Kimberley, not only Cronje, but the whole of the Boer force which was not engaged in Natal. I should have then been obliged either to march across the veld against this increased force, or to have transported the greater portion of my troops by rail to the Modder River camp (if the railway could have been kept intact, which was hardly likely, seeing how weakly it was necessarily guarded and the number of Boers who would have been available to destroy it), and then to turn the Magersfontein position. To carry out either of these operations, and for the onward advance on an extended front to Pretoria, at least the same amount of transport would have been required as was needed for the march from Modder River camp to Bloemfontein. But this would not have been forthcoming had I adopted the railway line to Bloemfontein and not organised the system of transport directly I arrived at the Cape.
"I felt convinced that an advance on Bloemfontein must draw the Free Staters back from Kimberley and Natal, and that the occupation of their capital would render the Boer positions to the south of the Orange river untenable. To carry out this scheme, as large a force as could be collected was necessary, as the enemy had through railway communication (about two days' journey) between Natal and Bloemfontein, and could transfer a considerable portion of their forces from one of the theatres of the war to the other in infinitely less time than we could. Moreover, rapidity was essential in concentrating this force and making an advance towards Bloemfontein, as Ladysmith and Kimberley were, so far as I know, only provisioned for a very limited time."
His reason for deciding against the railway through Jacobsdal.
It will be seen that Lord Roberts rejected Sir R. Buller's suggestion that a railway should be made through Jacobsdal to Bloemfontein. Colonel Girouard had estimated that this line could be constructed at the rate of a mile a day without interfering with the traffic for the supply of the troops, and, in an offer made to the Home Government by a private firm, hope had been held out that the work might be carried through at the rate of five or six miles a day, or in other words, that, assuming fighting conditions to be favourable, the whole would be finished in about a month. The latter estimate seemed altogether too sanguine. Moreover, the practical difficulty of guarding those employed on the required task from the raids of a mobile enemy would have been very great. Finally, the chance of surprise would have been lost, and, hard to secure as secrecy in, military projects had been found in South Africa, Lord Roberts was certain that to obtain decisive results the complete concealment of his plan of operations was essential.