GEO. B. MCCLELLAN."
"FREDERICK CITY, MD., September 13, 1862, 11 P.M.
("Received 1 P.M., September 14.)
"MAJOR-GENERAL H. W. HALLECK,
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 dispatch 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,
McClellan's supposed to have had Lee's plans according to this letter, yet he doesn't decisively win at Antietam (Sharpsburg). He won the battle strategically, but tactically it's been said to be a draw. I'm not certain he could have forced Lee to surrender if he couldn't decisively win the battle even with Lee's battle plans in hand.