Instead of attempting to turn the Enemy's right, and cut off his communications with Richmond and the South, McDowell has now determined to attack the Enemy's left, cut his communication, via the Manassas Gap railroad, with Johnston's Army,—still supposed by him to be in the Valley of the Shenandoah—and, taking him in the left flank and rear, roll him upon Manassas, in disorder and defeat—with whatever might follow.
That is the plan—in its general features. In executing it, Blenker's Brigade of Miles's Division is to remain at Centreville as a reserve, throwing up intrenchments about its Heights, upon which to fall back, in case of necessity; Davies's Brigade of the same Division, with Richardson's Brigade of Tyler's Division—as the Left Wing—are to demonstrate at Blackburn's Ford, toward the Enemy's right; Tyler's other three brigades, under Keyes, Schenck, and Sherman, are to feign an attack on the Enemy's left, posted behind the strongly-defended Stone Bridge over which the Warrenton turnpike, running Westward, on its way from Centreville to Warrenton, crosses Bull Run stream; while the strong divisions under Hunter and Heintzelman—forming McDowell's Right Wing—are to follow Tyler's Division Westward down the turnpike to a point within one mile and a half of the Stone Bridge, thence, by cross-road, diverge several miles to the North, then sweep around gradually to the West, and then Southwardly over Bull Run at Sudley Springs Ford, swooping down the Sudley road upon the Enemy's left flank and rear, near Stone Bridge, rolling it back toward his center, while Tyler's remaining three brigades cross the bridge and join in the assault. That is the whole plan in a nutshell.
It has been McDowell's intention to push forward, from Centreville along the Warrenton Pike a few miles, on the evening of this Military conference; but he makes his first mistake, in allowing himself to be dissuaded from that, by those, who, in his own words, "have the greatest distance to go," and who prefer "starting early in the morning and making but one move."
The attacking divisions now have orders to march at 2:30 A. M., in order "to avoid the heat," which is excessive. Tyler's three immediate brigades—or some of them—are slow in starting Westward, along the Warrenton Pike, to the Stone Bridge; and this leads to a two or three hours delay of the divisions of Hunter and Heintzelman, before they can follow that Pike beyond Centreville, and commence the secret detour to their right, along the cross-road leading to Sudley Springs.
At 6:30 A.M., Tyler's Artillery gets into position, to cannonade the Enemy's batteries, on the West Bank of Bull Run, commanding the Stone Bridge, and opens fire. Half an hour before this, (at 6 A.M.), the Rebel artillerists, posted on a hill South of the Pike, and 600 yards West of the bridge, have caught sight of Tyler's Union blue-jackets. Those of the Rebel gunners whose eyes are directed to the North-East, soon see, nearly a mile away, up the gradual slope, a puff of blue smoke. Immediately the bang of a solitary rifle cannon is heard, and the scream of a rifled shot as it passes over their heads. At intervals, until past 9 A.M., that piece and others in the same position, keep hammering away at the Rebel left, under Evans, at Stone Bridge.
The Rebel response to this cannonade, is very feeble. McDowell observes this. He suspects there has been a weakening of the Enemy's force at the bridge, in order to strengthen his right for some purpose. And what can that purpose be, but to throw his augmented right upon our left, at Blackburn's Ford, and so, along the ridge-road, upon Centreville? Thus McDowell guesses, and guesses well. To be in readiness to protect his own left and rear, by reenforcing Miles's Division, at Centreville and along the ridge to Blackburn's Ford, he temporarily holds back Howard's Brigade of Heintzelman's Division at the point where the cross-road to Sudley Springs Ford—along which Hunter's Division, followed by the Brigades of Franklin and Wilcox, of Heintzelman's Division, have already gone—intersects the Warrenton Pike.
It is 9 o'clock. Beauregard, as yet unaware of McDowell's new plan, sends an order to Ewell, on his right, to hold himself ready "to take the offensive, at a moment's notice,"—and directing that Ewell be supported in his advance, toward Sangster's cross-roads and the rear of Centreville, by Holmes's Brigade. In accordance with that order, Ewell, who is "at Union Mills and its neighborhood," gets his brigade ready, and Holmes moves up to his support. After waiting two hours, Ewell receives another order, for both Ewell and Holmes "to resume their places." Something must have occurred since 9 o'clock, to defeat Beauregard's plan of attack on Centreville—with all its glorious consequences! What can it be? We shall see.
While Tyler's Artillery has been cannonading the Rebel left, under Evans, at Stone Bridge,—fully impressed with the prevailing Union belief that the bridge is not only protected by strong masked batteries, heavy supports of Infantry, and by abatis as well as other defenses, but is also mined and ready to be blown up at the approach of our troops, when in reality the bridge is not mined, and the Rebel force in men and guns at that point has been greatly weakened in anticipation of Beauregard's projected advance upon Centreville,—the Union column, under Hunter and Heintzelman, is advancing from Centreville, in the scorching heat and suffocating dust of this tropical July morning, slowly, but surely, along the Warrenton Pike and the cross-road to Sudley Springs Ford—a distance of some eight miles of weary and toilsome marching for raw troops in such a temperature—in this order: Burnside's Brigade, followed by Andrew Porter's Brigade,—both of Hunter's Division; then Franklin's Brigade, followed by Willcox's Brigade,—both of Heintzelman's Division.
It is half past 9 o'clock; before Burnside's Brigade has crossed the Bull Run stream, at Sudley's Ford, and the head of Andrew Porter's Brigade commences to ford it. The troops are somewhat slow in crossing. They are warm, tired, thirsty, and as to dust,—their hair and eyes and nostrils and mouths are full of it, while most of the uniforms, once blue, have become a dirty gray. The sky is clear. The sun already is fiercely hot. The men stop to drink and fill their canteens. It is well they do.
McDowell, who has been waiting two or three hours at the turn, impatient at the delay, has ridden over to the front of the Flanking column, and now reaches Sudley's Ford. He feels that much valuable time is already lost. His plan has, in a measure, been frustrated by delay. He had calculated on crossing Bull Run, at Sudley's Ford, and getting to the rear of the Enemy's position, at Stone Bridge, before a sufficient Rebel force could be assembled to contest the Union advance. He sends back an aide with orders to the regimental commanders in the rear, to "break from column, and hurry forward separately, as fast as possible." Another aide he sends, with orders to Howard to bring his brigade across-fields. To Tyler he also sends orders to "press forward his attack, as large bodies of the Enemy are passing in front of him to attack the division (Hunter's) which has passed over."