The enemy is drawn up in line of battle on a ridge about two miles beyond Potomac [.] They are in full view [.] Their line is a perfect one about a mile and a half long. We
havecan have equally good position as they now occupy. Richardson is forming his line to attack. We are lacking in artillery Tidball’s being the only artillery available hurry up more guns we can get good position for two hundred guns. Longstreet is in command and has forty cannon that we know of. We can employ all the troops you can send us.
Library of Congress, George B. McClellan Papers (A80: Roll 32)
In the McClellan Papers, this dispatch is dated September 17, 1862. Yet, because of its content and the other dispatches which Custer sent McClellan that day (at least from those I saw in the McClellan Papers thus far), this must have been on the 15th, and whomever cataloged the papers simply mislabeled it. The mention of Tidball's Battery, Richardson's Division, and the defensive positions of Lee's army outside of Sharpsburg all suggest that this was a dispatch sent on the 15th, making it an early assessment of the Confederate position outside of Sharpsburg.
In the Sears collection of McClellan's Civil War correspondence, a reference is made to this dispatch in a footnote where Sears only included the following portion: "The enemy is drawn up in line of battle on a ridge about two miles beyond [Keedysville]. They are in full view. Their line is a perfect one about a mile and a half long.... Longstreet is in command and has forty cannon that we know of." Sears omitted the lines where Custer notes the lack of Federal artillery at the front, as well as the mention of Tidball’s battery and Richardson’s division. It should be noted that, while Custer's dispatch clearly says Lee is two miles beyond the Potomac, he was either mistaken or confused in his wording. As Sears indicated in his reference to this dispatch, Custer meant that Lee was two miles beyond Keedysville, not the Potomac River. On the 15th, Lee was indeed two miles beyond Keedysville, drawn up outside of Sharpsburg. If Custer did indeed mean the Potomac, then using beyond was a poor word choice, as it suggests that Lee's army was past the river, rather than a few miles away from it, still on Maryland soil. However, given the lack of punctuation and the hurried nature of the writing, I doubt Custer took a moment to proofread the message he was sending along. Either way, it is a fascinating dispatch from an officer who would go on to be one of the more famous generals of the war, and of the 19th century, offering one of the first Union assessments of Lee’s position outside of Sharpsburg.