WAR DEPARTMENT, Washington, December 16, 1862.

Major-General BURNSIDE, Falmouth, Va.:

The President desires that you report the reasons of your withdrawal as soon as possible.

H. W. HALLECK,

General-in-Chief.

HEADQUARTERS ARMY OF THE POTOMAC, December 16, 1862-5.30 p.m. [Received 6 p.m.]

Your dispatch is received. The army was withdrawn to this side of the river because I felt the positions in front could not be carried, and it was a military necessity either to attack or retire. A repulse would have been disastrous to us.

I hope this explanation will be satisfactory to the President. The army was withdrawn at night, without the knowledge of the enemy, and without loss either of property or men.

I have sent Colonel Aspinwall to you this afternoon, who can give you full accounts of the affairs at the present moment. I will send you a more full dispatch to-morrow.

A. E. BURNSIDE,
Major-General, Commanding.

Major-General HALLECK.

HEADQUARTERS ARMY OF THE POTOMAC, December 17, 1862.

I have the honor to offer the following reasons for moving the Army of the Potomac across the Rappahannock sooner than was anticipated by the President, Secretary, or yourself, and for crossing at a point different from the one indicated to you at our last meeting at the President's:

During my preparations for crossing at the place I had at first selected, I discovered that the enemy had thrown a large portion of his force down the river and elsewhere, thus waking his defenses in front; and I also thought I discovered that he did not anticipate the crossing of our whole force at Fredericksburg; and I hoped, by rapidly throwing the whole command over at that place, to separate, by a vigorous attack, the forces of the enemy on the river below from the forces behind and on the crests in the rear of the town, in which case we should fight him with great advantages in our favor. To do this we had to gain a height on the extreme right of the crest, which height commanded a new road, lately built by the enemy for purposes of more rapid communication along his lines; which point gained, his positions along the crest would have been scarcely tenable, and he could have been driven from them easily by an attack on his front, in connection with a movement in rear of the crest.

How near we came to accomplishing our object future reports will show. But for the fog and unexpected and unavoidable delay in building the bridges, which gave the enemy twenty-four hours more to concentrate his forces in his strong positions, we would almost certainly have succeeded; in which case the battle would have been, in my opinion, far more decisive than if we had crossed at the places first selected. As it was, we came very near success. Failing in accomplishing the main object, we remained in order of battle two days-long enough to