COLONEL: I have the honor to submit the following report of the battle of the 21st of July, near Manassas, Va. It has been delayed till this time from the inability of the subordinate commanders to get earlier a true account of the state of their commands.

In my communication to you of the 20th ultimo, I stated it as my intention to move that afternoon and drive the enemy from the east side of Bull Run, so as to enable the engineers to make a sufficiently accurate reconnaissance to justify our future movements. Later in the day they had obtained enough information of the passages across the stream to dispense with this reconnaissance, and it was decided to move without further delay.

It had been my intention to move the several columns out on the road a few miles on the evening of the 20th, so that they would have a shorter march in the morning; but I deferred to those who had the greatest distance to go, and who preferred starting early in the morning and making but one move.

On the evening of the 20th ultimo my command was mostly at or near Centreville. The enemy was at or near Manassas, distant from Centreville about seven miles to the southwest. Centreville is a village of a few houses, mostly on the west side of a ridge running nearly north and south. The road from Centreville to Manassas Junction runs along this ridge, and crosses Bull Run about three miles from the former place. The Warrenton turnpike, which runs nearly east and west, goes over this ridge through the village, and crosses Bull Run about four miles from it, Bull Run having a course between the crossings from northwest to southeast.

The First Division (Tyler's) was stationed as follows: One brigade on the north side of the Warrenton turnpike and on the eastern slope of the Centreville ridge; two brigades on the same road and a mile and a half in advance to the west of the ridge; and one brigade on the road from Centreville to Manassas where it crosses Bull Run at Blackburn's Ford, where General Tyler had the engagement of the 18th ultimo.

The Second Division (Hunter's) was on the Warrenton turnpike, one mile east of Centreville.

The Third Division (Heintzelman's) was on a road known as the old Braddock road, which comes into Centreville from the southeast about a mile and a half from the village.

The Fifth Division (Miles') was on the same road with the Third Division, and between it and Centreville.

A map, which is herewith, marked A, will show these positions better than I describe them.

Friday night a train of subsistence arrived, and on Saturday its contents were ordered to be issued to the command, and the men required to have three days' rations in their haversacks. (See appendix herewith, marked B.)

Saturday orders (copy herewith, marked c) were issued for the available force to march.

As reported to you in my letter of the 19th ultimo, my personal reconnaissance of the roads to the south had shown that it was not practicable to carry out the original plan of turning the enemy's position on their right. The affair of the 18th at Blackburn's Ford showed he was too strong at that point for us to force a passage there without great loss, and if we did, that it would bring us in front of his strong position at Manassas, which was not desired.

Our information was that the stone bridge over which the Warrenton road crossed Bull Run to the west of Centreville was mined, defended by a battery in position, and the road on his side of the stream impeded by a heavy abatis. The alternative was, therefore, to turn the extreme left of his position.

Reliable information was obtained of an undefended ford about three miles above the bridge, there being another ford between it and the bridge, which was defended. It was therefore determined to take the road to the upper ford, and, after crossing, to get behind the forces guarding the lower ford and the bridge, and after occupying the Warrenton road east of the bridge to send out a force to destroy the railroad at or near Gainesville, and thus break up the communication between the enemy's forces at Manassas and those in the Valley of Virginia before Winchester, which had been held in check by Major-General Patterson.

Brigadier-General Tyler was directed to move with three of his brigades on the Warrenton road, and commence cannonading the enemy's batteries, while Hunter's division, moving after him, should, after passing a little stream called Cub Run, turn to the right and north, and move by a wood road around to the upper ford, and then turn south and get behind the enemy; Colonel Heintzelman's division to follow Hunter's as far as the turning-off place to the lower ford, where he was to cross after the enemy should have been driven out by Hunter's division; the Fifth Division (Miles') to be in reserve on the Centreville ridge.

I had felt anxious about the road from Manassas by Blackburn's Ford to Centreville along this ridge, fearing that, whilst we should be in force to the front and endeavoring to turn the enemy's position, we ourselves should be turned by him by this road. For if he should once obtain possession of this ridge, which overlooks all the country to the west to the foot of the spurs of the Blue Ridge, we should have been irretrievably cut off and destroyed. I had, therefore, directed this point to be held in force, and sent an engineer to extemporize some field works to strengthen the position.

The Fourth Division (Runyon's) had not been brought to the front farther than to guard our communications by way of Vienna and the Orange and Alexandria Railroad. His advanced regiment was about seven miles in rear of Centreville.

The divisions were ordered to march at 2.30 o'clock a.m., so as to arrive on the ground early in the day, and thus avoid the heat which is to be expected at this season. There was delay in the First Division getting out of its camp on the road, and the other divisions were, in consequence, between two and three hours behind the time appointed--a great misfortune, as events turned out. The wood road leading from the Warrenton turnpike to the upper ford was much longer than we counted upon, the general direction of the stream being oblique to the road and we having the obtuse angle on our side.

General Tyler commenced with his artillery at 6.30 a.m., but the enemy did not reply, and after some time it became a question whether he was in any force in our front, and if he did not intend himself to make an attack, and make it by Blackburn's Ford. After firing several times, and obtaining no response, I held one of Heintzelman's brigades in reserve, in case we should have to send any troops back to re-enforce Miles' division. The other brigades moved forward as directed in the general order.