By a well-combined series of maneuvers Sherman then forced Johnston to fall back or be hopelessly outflanked. Johnston, with equal skill, crossed the Chattahoochee under cover of the strongly fortified bridgehead which he had built unknown to Sherman. But Sherman, with his double numbers, could always hold Johnston with one-half in front while turning his flank with the other. So even the Chattahoochee was safely crossed on the seventeenth of July and the final move against Atlanta was begun. That same night Johnston's magnificent skill was thrown to the winds by Davis, who had ordered the bold and skillful but far too headlong John B. Hood to take command and "fight." Five days later Hood fought the battle of Atlanta. Just as Sherman was closing in to entrench for a siege Hood attacked his extreme left flank with the utmost resolution, driving it in and completely enveloping it. But Sherman was not to be caught. Knowing that only a part of Hood's army could be sent to this attack while the rest held the lines of Atlanta, Sherman left McPherson's veteran Army of the Tennessee to do the actual fighting, supported, of course, by the movement of troops on their engaged right. McPherson was killed. Logan ably replaced him and won a hard-fought day. Hood's loss was well over eight thousand; Sherman's considerably less than half. On the twenty-eighth Hood attacked the extreme right, now commanded by General O. O. Howard in succession to McPherson, whose Army of the Tennessee again did most distinguished service, especially Logan's Fifteenth Corps near Ezra Church. The Confederates were again defeated with the heavier loss. After this the siege continued all through the month of August. While Hood was trying to keep Sherman off Atlanta Grant was trying to make a breach at Petersburg. Grant gave Meade "minute orders on the 24th [of July] how I wanted the assault conducted," and Meade elaborated the actual plan with admirable skill except in one particular--that of the generals concerned. Burnside was ordered to use his corps for the assault, and he chose Ledlie's division to lead. The mine was on an enormous scale, designed to hold eight tons of powder, though it was only charged with four, and was approached by a gallery five hundred feet long. On the twenty-ninth Grant brought every available man into proper support of Burnside, whose other three divisions were to form the immediate support of Ledlie's grand forlorn hope.