HEADQUARTERS FOURTH ARMY CORPS, Yorktown, Va., April 14, 1863.

Major General H. W. HALLECK,
Commanding U. S. Army:

SIR: Major-General Dix arrived this morning and resumed command of the Department of Virginia.

During the nine days I was in temporary command of the department the approach of the enemy in great force down the Peninsula and upon Suffolk gave a serious aspect to affairs, and this paper is respectfully submitted as the result of my examinations and consequent conclusions while I was in command.

Of Peck's position and the surrounding country beyond Norfolk I had no ocular knowledge until the 6th instant, when I made a hasty visit to Suffolk by rail. Since that date I have made as careful examination of his defenses and passed over the other railroad from Norfolk and down the Nansemond River to Hampton Roads.

As I stated before in telegrams I consider our troops at Suffolk in a very critical situation, and it may be the rebels' boats that they have another Harper's Ferry affair on hand will be made good.

I have reflected on the following points:

1st. Is Peck secure against an attack, or is he able to resist an attack in his position?

2nd. Can the enemy cut his communication and invest him?

3rd. If the enemy should invest him have we the means to relieve him before he would be starved out?

4th. Can he retreat and take away his material?

On the above points I conclude as follows:

1st. He is secure against an attack on any front now accessible to the enemy, and he will not be seriously attacked (feints will be made) until he is invested. After he is invested he is not secure from an attack.

2nd. The enemy can cut his communications and invest him in spite of anything we can do to prevent him with the means north of Albemarle Sound and south of Hampton Roads and James River.

3rd. If the enemy does invest him we could not break the investment after it had existed three days and relieve Peck with any available means within the command of the Government.

4th. I cannot give a positive opinion on this point. I have had no time to examine the line of the retreat. The railroads are through the Dismal Swamp and are perfectly straight and the roadway narrow, and, on either side, an impracticable morass.

I assume that the Government knows Peck's strength and the amount of his supplies of provisions and ammunition. It is certain he has but a few days' supply of forage.

I have assumed all those facts of the last paragraph, and I have kept Napoleon's maxims in view (you called my attention to those maxims) in coming to my conclusions.

In regard to the Peninsula: If the line of Fort Magruder below Williamsburg is given up the enemy can go to Fort Monroe at once and possess everything outside the sand-spit on which the fort stands.

Yorktown, owing to the ravines around it, would be nearly as uncomfortable as Fort Magruder now is, and of no great value to the Government. If the upper line is abandoned I trust this most sickly place (Yorktown) may be also abandoned. I recommended its abandonment in August last when called on for my views.

With one gunboat on James River, stationed opposite Williamsburg,

39 R R-VOL XVIII