Four thousand infantry and one battery leave Washington at once for Manassas. Some 3,000 more will move in one or two days, and soon after some 3,000 additional. I will order Blenker to march on Strasburg and to report to you for temporary duty, so that, should you find a large force in your front, you can avail yourself of his aid as soon as possible. Please direct him to Winchester, thence to report to the Adjutant-General of the Army for orders; but keep him until you are sure what you have in front.

In regard to your own movements, the most important thing at present is to throw Jackson well back, and then to assume such a position as to enable you to prevent his return. As soon as the railway communications are re-established it will be probably important and advisable to move on Staunton, but this would require secure communications and a force of from 25,000 to 30,000 for active operations. It should also be nearly coincident with my own move on Richmond; at all events, not so long before it as to enable the rebels to concentrate on you and then return on me. I fear that you cannot be ready in time, although it may come in very well with a force less than that I have mentioned, after the main battle near Richmond. When General Sumner leaves Warrenton Junction, General Abercrombie will be placed in immediate command of Manassas and Warrenton Junction under your general orders. Please inform me frequently by telegraph and otherwise as to the state of things in your front.

I am, very truly, yours,

GEO. B. MCCLELLAN,

Major-General, Commanding.

P. S. - From what I have just learned it would seem that the regiments of cavalry intended for Warrenton Junction have gone to Harper's Ferry. Of the four additional regiments placed under your orders, two should as promptly as possible move by the shortest route on Warrenton Junction.

I am, sir, very respectfully, your obedient servant,

GEO. B. MCCLELLAN,

Major-General, Commanding.

Major General N. P. BANKS, Commanding Fifth Corps.

This letter needs no further explanation than to say that it was my intention, had the operations in that quarter remained under my charge, either to have resumed the defensive positions marked out in the letter of March 16, or to have advanced General Banks upon Staunton, as might in the progress of events seem advisable.

It is to be remembered that when I wrote the preceding and following letters of April 1 I had no expectation of being relieved from the charge of the operations in the Shenandoah Valley, the President's War Order, Numbers 3, giving no intimation of such an intention, and that so far as reference was made to final operations after driving Jackson back and taking such a position as to prevent his return, no positive orders were given in the letter, the matter being left for future consideration when the proper time arrived for a decision.

From the following letter to the Adjutant-General, dated April 1, 1862, it will be seen that I left for the defenses of the national capital and its approaches, when I sailed for the Peninsula, 73,456 men, with 109 pieces of light artillery, including the 32 pieces of light artillery, including the 32 pieces in Washington alluded to but not enumerated in my letter to the Adjutant-General. It will also be seen that I recommended other available troops in New York (more than 4,000) to be at once ordered forward to re-enforce them:.

HEADQUARTERS ARMY OF THE POTOMAC,
Steamer Commodore, April 1, 1862.

GENERAL: I have to request that you will lay the following communication before the honorable Secretary of War:

The approximate numbers and positions of the troops left near and in rear of the Potomac are as follows:

General Dix has, after guarding the railroads under his charge, sufficient to give him 5,000 for the defense of Baltimore and 1,988 available for the Eastern Shore, Annapolis, & c. Fort Delaware is very well garrisoned by about 400 men.

The garrisons of the forts around Washington amount to 10,600 men; other disposable troops now with General Wadsworth about 11,400 men.