In answering this question the political considerations must be first weighed. In short, the purpose—the great purpose—of the invasion must be penetrated. That being done, the military problem would easily solve itself.
It was not to be supposed that Lee had invaded Pennsylvania solely for the purpose of taking a few small towns, or even a large one, like Harrisburg, or of filling up his depleted magazines. He was evidently after larger game. His ultimate aim, clearly, was to capture Washington, as a signal defeat of the Union army would easily enable him to do. It would crown the campaign brilliantly, would fulfil the hopes, and beyond doubt or cavil ensure the triumph, of the Confederacy. It is true that Meade's orders held him down to a defence of the national capital first and foremost; in no sense, then, was he the master of his own acts: yet he showed none the less sagacity, we think, in concluding that Lee would presently be found on the east side of the mountains, and in preparing to meet him there, not astride the mountains as Hooker had proposed doing, but with his whole army more within his reach. Meade was prudent. He would err, if at all, on that side; yet the result vindicated his judgment sooner than was thought for.
This being settled, there still remained the question of relieving Pennsylvania. The enemy's presence there was an indignity keenly enough felt on all sides, but to none was it such a home-thrust as to the Pennsylvanians in the Union army, at the head of whom was Meade himself.[25]
Meade's Plans.
Though Hooker's plan promised excellent results here, Meade was fearful lest Lee should cross the Susquehanna, and take Harrisburg before he could be stopped. To prevent this the army must be pushed forward. Meade, therefore, at once drew back the left wing toward Frederick, thus giving up that plan in favor of one which he himself had formed; namely, of throwing the army out more to the northeast, the better to cover Baltimore from attack, should that be Lee's purpose, as Meade more than suspected. Selecting Westminster, therefore, as his base from this time forth, and the line of Big Pipe Creek, a little to the north of that place, as his battle-ground, Meade now set most of the army in motion in that direction, leaving Frederick to the protection of a rear-guard.
Left Flank Forward.
Right Flank refused.
The army now marched with its left wing thrown forward toward South Mountain, Buford's cavalry toward Fairfield, to clear that flank, the First and Eleventh Corps toward Emmettsburg, the Third and Twelfth toward Middleburg, the Fifth to Taneytown, the Second to Uniontown, and the Sixth, on the extreme right, to New Windsor.
Two other divisions of Union cavalry, Kilpatrick's and Gregg's, marched one on the right flank, the other in front, with orders to keep the front and flanks of the army well scouted and protected.