It does not necessarily follow from the failure of a tactical scheme that it was unsuited to the occasion; but the failure of February 18 was due to one of three causes: to the defects of the scheme, to the mode of its execution, or to the Boer external attacks. It was not a scheme which either Kelly-Kenny or Colvile would have devised if left to himself, and it is very doubtful whether Kitchener had Lord Roberts' direct authority for it. But assuming that it offered a better chance of crippling the enemy at large than the alternative of an investment, it was so hastily devised and so clumsily pursued that it became hourly more difficult to carry through, until it was finally subverted by De Wet. Many of the commanding officers had as little knowledge of Kitchener's purpose as the pawns which are moved by the hands of the chess player. The conclusion seems to be that but for De Wet's intrusion the brute force of the investors might possibly have prevailed. But the final cause of the failure was Lord Roberts' error of judgment in putting Kitchener into virtual command of the Vendutie Drift force, thereby superseding senior officers of greater tactical ability. The complications arising out of brevet rank and local rank, grades peculiar to the British Army,[37] were already sufficiently disturbing, and yet Kitchener was irregularly advanced by a few words in a private letter from Lord Roberts to Kelly-Kenny. In his report on the day's work to Lord Roberts at Jacobsdaal, Kitchener could only say that he hoped to do something more definite on the morrow. Lord Roberts at once ordered him to be reinforced, and being now convalescent set out for Paardeberg, where he arrived during the forenoon of February 19. It is significant that Lord Roberts did not renew the assault on the laager, and confined himself to operations against Kitchener's Kopje, thus reverting to the scheme of investment proposed by Kelly-Kenny on the previous day. The burghers evacuated the big donga during the night.