“I have the whole rebel force in front of me, but am confident, and no time shall be lost. I have a difficult task to perform, but with God’s blessing will accomplish it. I think Lee has made a gross mistake, and that he will be severely punished for it. The army is in motion as rapidly as possible. I hope for a great success if the plans of the rebels remain unchanged. We have possession of Catoctin. I have all the plans of the rebels, and will catch them in their own trap if my men are equal to the emergency. I now feel that I can count on them as of old. All forces of Pennsylvania should be placed to co-operate at Chambersburg. My respects to Mrs. Lincoln. Received most enthusiastically by the ladies. Will send you trophies. All well, and with God’s blessing will accomplish it.
“Geo. B. McClellan.”
“Frederick City, Md., September 13, 1862, 11 P.M.
(“Received 1 P.M., September 14.)
“Major-General H. W. Halleck,
“General-in-Chief:
“An order from General R. E. Lee, addressed to General D. H. Hill, which has accidentally come into my hands this evening,—the authenticity of which is unquestionable,—discloses some of the plans of the enemy, and shows most conclusively that the main rebel army is now before us, including Longstreet’s, Jackson’s, the two Hills’s, McLaws’s, Walker’s, R. H. Anderson’s, and Hood’s commands. That army was ordered to march on the 10th, and to attack and capture our forces at Harper’s Ferry and Martinsburg yesterday, by surrounding them with such a heavy force that they conceived it impossible they could escape. They were also ordered to take possession of the Baltimore and Ohio Railroad; afterwards to concentrate again at Boonsborough or Hagerstown. That this was the plan of campaign on the 9th is confirmed by the fact that heavy firing has been heard in the direction of Harper’s Ferry this afternoon, and the columns took the roads specified in the order. It may, therefore, in my judgment, be regarded as certain that this rebel army, which I have good reasons for believing amounts to 120,000 men or more, and know to be commanded by Lee in person, intended to attempt penetrating Pennsylvania. The officers told their friends here that they were going to Harrisburg and Philadelphia. My advance has pushed forward to-day and overtaken the enemy on the Middletown and Harper’s Ferry roads, and several slight engagements have taken place, in which our troops have driven the enemy from their position. A train of wagons, about three-quarters of a mile long, was destroyed to-day by the rebels in their flight. We took over fifty prisoners. This army marches forward early to-morrow morning, and will make forced marches, to endeavor to relieve Colonel Miles, but I fear, unless he makes a stout resistance, we may be too late.
“A report came in just this moment that Miles was attacked to-day, and repulsed the enemy, but I do not know what credit to attach to the statement. I shall do everything in my power to save Miles if he still holds out. Portions of Burnside’s and Franklin’s corps move forward this evening.
“I have received your despatch of ten A.M. You will perceive, from what I have stated, that there is but little probability of the enemy being in much force south of the Potomac. I do not, by any means, wish to be understood as undervaluing the importance of holding Washington. It is of great consequence, but upon the success of this army the fate of the nation depends. It was for this reason that I said everything else should be made subordinate to placing this army in proper condition to meet the large rebel force in our front. Unless General Lee has changed his plans, I expect a severe general engagement to-morrow. I feel confident that there is now no rebel force immediately threatening Washington or Baltimore, but that I have the mass of their troops to contend with, and they outnumber me when united.
“Geo. B. McClellan,
“Major-General.”[59]
With the knowledge afforded by securing Lee’s “lost order” the passes of the South Mountain became important points. If he could force them, McClellan might fall on the divided columns of the Confederates and reach Harper’s Ferry in time to save its garrison; but Lee received intelligence of his only moderate forward movement, and, without knowing then how it came to be made, recalled a force to make resistance, and, so supplementing or complementing by his rapid moves the Federal commander’s slowness, saved his campaign from the disastrous failure that threatened it.
General McClellan claimed to have been more vigorous in pursuit after he received the “lost despatch,” but events do not support the claim. He had time after the despatch was handed him to march his army to the foot of South Mountain before night, but gave no orders, except his letter to General Franklin calling for vigorous action, which was afterwards tempered by caution to wait for developments at Turner’s Pass. He gave no intimation of the despatch to his cavalry leader, who should have been the first to be advised of the points in his possession. General Pleasonton had pushed the Confederate cavalry back into the mountains long before night of the 13th under his instructions of the 12th. Had he been informed of the points known by his chief in the afternoon, he would have occupied South Mountain at Turner’s Pass before any of the Confederate infantry was there or apprised of his approach. General McClellan’s orders for the 14th were dated,—