The Boers, who had captured at Dundee some intelligence papers which disclosed the original plan of campaign, were now more than ever convinced that the British Army must advance by way of Norval's Pont and Bethulie, and did not discover their error until it was too late to rectify it.[34] When Lord Roberts had made all his preparations, which involved the entire reorganization of the transport, and the raising of a considerable force of mounted troops, for his march of 100 miles across the veld eastward from the railway, the secret was disclosed to Kelly-Kenny and French on February 1. This plan of a flank march had also suggested itself to Buller, who proposed it in a memorandum which Lord Roberts found on his arrival in Capetown; but as Buller's scheme included the construction of a railway across the veld, and limited the advance of the Army to the rate at which the line could be pushed forward, it did not fall in with Lord Roberts' ideas.
Meanwhile Cronje was not perturbed by the reports of troops coming up the Western line, and was confident that they only indicated a renewed but isolated attack on Magersfontein. He had no doubt that if necessary he could always fall back upon Kimberley and retreat towards the Transvaal; and the demonstrations made by Methuen westwards in the direction of Koedoesberg Drift served the double purpose of warning a disaffected region and of diverting Cronje's attention from the flank on which he was to be attacked and which he believed to be secure.
The two months following the arrival of Lord Roberts in South Africa were the only brilliant period of a dreary war which lasted nearly three years, and will perhaps save it from being quoted in military history as the most sluggish campaign of recent times. In each of the two objects of strategy, namely to avoid fighting the enemy on ground of his own choosing, and to compel him to fight under unfavourable conditions, Lord Roberts was extraordinarily successful. There was a light touch, an ingenuity, in his swift and silent strategy which contrasted strongly with the heavy and dull methods which had hitherto controlled the action. While Buller was talking about his tedious railway across the veld, and Milner at Capetown was dismalling the situation and discouraging the advance, Lord Roberts had in effect entered the capital of the Free State and seemed to have completed half his task. The Boers were hypnotized and deceived not only by signs from which they drew wrong inferences, but also by bogus orders which it was arranged should come under their notice and which were simultaneously cancelled in cipher: and when too late they awoke from the bewilderment, they began to scuttle to and fro like rabbits in a warren. There is good reason to believe that if the strategic ability of Lord Roberts could have been united in one mind to the determination of Lord Kitchener the war would have been over in a year.
On February 8 Lord Roberts arrived at Modder River, where he found bad news awaiting him. Buller had failed at Vaalkrantz, and the diamond men of Kimberley were threatening to capitulate. By February 13 30,000 combatants, some of whom in order to preserve the illusion had been kept in the centre until the last moment, were in readiness at various points between the Orange and the Modder. The immediate problem before Lord Roberts was the relief of Kimberley in combination with the cornering of Cronje. In the background was the Natal trouble. Buller was again helplessly wringing his hands and reaching round to find excuses for his misadventures. Lord Roberts wisely left him alone and went on with his own work. He saw what Buller refused to see, that the Tugela could be crossed at Magersfontein and Ladysmith relieved at a drift of the Modder River.
On February 11 Lord Roberts set his army in motion; and the operations of the next few days may be summarised with sufficient accuracy as a cavalry raid northwards, but avoiding Cronje's left flank at Brown's Drift, to relieve Kimberley; combined with an infantry advance to cut him off. It was not possible to make the initial movements in the direction of the eventual advance, as the Magersfontein-Brown's Drift quadrant N.E. of Modder River was strongly held by the enemy, and disallowed a cavalry advance from below the junction of the Riet and the Modder in the direction of Kimberley except by a westerly detour which could not be accommodated to the general scheme. In order to strike the practicable drifts on the two rivers above their confluence, it was necessary for the advance to be made along the curve of a parabola which issued from Modder River Station in a S.E. direction, and in a sixty-mile circuit crossed the rivers and finally approached Kimberley, only twenty miles distant from the starting point, almost in the opposite direction.
At midday on February 11 the Cavalry Division under French reached Ramdam, a farm east of Graspan and fronting the drifts of the Riet, where the Army was being concentrated for the advance. Some hours elapsed before Cronje became aware that French had trekked away to the S.E., and to his slow and sullen spirit the movement did not appear to have much significance. He was persuaded that the British never trusted themselves much more than a day's march away from a railway. It was only a demonstration, a reconnaissance. He did, however, take certain precautions which, if they had been devised with a true appreciation of the situation and intelligently carried out, might have seriously checked French.
He assumed that the initial direction of French's march would be continued indefinitely towards Koffyfontein, possibly even that it was a retirement from the Modder River position caused by bad news from the centre, and he sent a commando of observation, under C. de Wet, up the right bank of the Riet. The most adroit and skilful movement of the war had now begun without Cronje's comprehending its object.