HEADQUARTERS DEPARTMENT OF THE SOUTH,
Hilton Head, S. C., September 20, 1862.

Major-General HALLECK,

General-in-Chief, Washington, D. C.:

GENERAL: I have the honor to report that in obedience to your orders I have assumed command of the Department of the South.

I have already inspected the troops stationed at Beaufort, at Fort Pulaski, and on Hilton Head Island. I find their condition, as well as that of the forts and other works, highly satisfactory. Brigadier-General Terry has already been ordered to an inspection of the more southern posts of this department. He left Hilton Head on the 16th instant, and In anticipate his return in a few days. The health of the officers and soldiers I find to be generally good.

I regret to say that a small detachment of soldiers which arrived at this post on the Delaware from Key West has been found to be infected with yellow fever. Every precaution appears to have been taken by the commanding officer in subjecting the vessel to a vigorous and prolonged quarantine. After the troops were landed a few Cases of fever occurred, two or three of which have resulted in death. The medical director does not anticipate at present that the disease will spread. I inclose a copy of his report.

I need not say to you, general, how anxious I am to commence active operations against the enemy. I am entirely confident, from the slight examination I have been able to make, that the most important results may be reached at an early day, provided it be possible to send to this department a moderate additional force.

I most earnestly and respectfully beg that my old division, so long under my command, may again be placed under my orders by transferring them to the Department of the South.

I am happy to say that the most cordial feeling has already been established between Admiral DuPont and myself, and I look forward with great pleasure to the early commencement of active operations, in which the land and naval forces will act in conjunction. I deem it my duty to omit no opportunity to harass and annoy the enemy, and shall study with great care, not only the approaches to Charleston and Savannah, but to all the intermediate points on the line of the railway uniting these two cities.

In case my old division could be returned to my command and another division from the new levies I should then have a force sufficiently strong to strike the most decisive blows. The moral and military effect of the capture and occupation of Charleston and Savannah, in my opinion, cannot be overestimated. Every duty that passes adds to the strength of the defenses in process of construction by the enemy before these two important cities.

I do not intend to importune the Government to increase the number of troops under my command on my own personal account, but I should be wanting in the discharge of the duty which devolves upon me as commander of the Department of the South I did not represent to the Government in the strongest terms the vast importance of the early capture of Charleston.

Very respectfully, your obedient servant,

O. M. MITCHELL,

Major-General, Commanding.