Accomplished soldier that he was, he saw clearly that the "objective" of his campaign must be the crushing of Lee and the enforced retreat of the Confederates to the southern side of the Potomac. To that end McClellan desired to employ the utmost force within call. He had about 70,000 men against Lee's 45,000, but he urgently asked for the 11,000 additional men who were guarding Harper's Ferry and Martinsburg. He asked that those untenable positions should be abandoned and their defenders added to the already superior force with which he was to try conclusions again with the masterful adversary who had so conspicuously defeated him before Richmond. But General Halleck was now in chief command and he refused this request. His refusal to order the evacuation of the two untenable positions and to add their important garrisons to McClellan's force, seriously embarrassed Lee and contributed, in an indirect but effective way, to the defeat of those purposes with which the Confederate chieftain had undertaken his hazardous campaign. Lee had assumed, quite as a matter of course, that upon his passage of the Potomac, Martinsburg and Harper's Ferry would be evacuated, being obviously untenable. But in fact they were not abandoned. So Lee was compelled to pause and to send Jackson back to the south side of the river to secure control of positions that commanded his own only secure line of retreat in case of disaster. This caused a very serious delay in Lee's operations, and in such a campaign of aggression, promptitude and swiftness are all important to the accomplishment of desired results. Jackson went back across the river to assail Harper's Ferry from the South. In the meanwhile McLaws, Walker and D. H. Hill seized and held respectively Maryland Heights, Loudon Heights and Boonesboro Pass, while Lee with the remainder of his now dangerously divided army advanced to Hagerstown in search of food supplies. Jackson did his part of the work perfectly, as it was his custom to do. He drove his enemy out of Martinsburg and captured Harper's Ferry with 11,500 prisoners, seventy-three serviceable guns and important stores. But in the meanwhile Lee's army had been scattered in a very perilous way, and in his anxiety for its reconcentration, he wrote out an order, giving in detail his instructions to his several subordinates. A copy of this order somehow fell into McClellan's hands. It clearly revealed to him Lee's divided and scattered condition, and for once in his life McClellan hurried. If he, with 70,000 men, could manage to attack in detail the several widely separated fragments of Lee's army which had now been reduced by casualties to less than a total of 40,000, surely he must win. Accordingly he hurriedly pushed forward, hoping to carry Turner's and Crampton's Gaps in the South Mountain before Lee could concentrate for their defense.