Mount Pleasant, entering in light-draught steamers by one of three inlets south of Bull's Bay. This will take Sullivan's Island in reverse, and also command the city. I am ready to attempt this at any time that you may think best. I shall want four or five of such light-draught steamers as those built by Mr. Wiard and sent to Fort Monroe; two more are ready to launch in New York. As far as I know thus far, this operation promises greatly in favor of success. To make it sure would, of course, require a considerable increase of my force. But I am ready to undertake it now if the emergency of military affairs in Virginia requires a powerful demonstration here. I think I may be able to effect a partial surprise, and then, if the navy co-operates strongly, we will have the garrison of Sullivan's Island at our mercy. I am thus particular in stating all these points, because I understand you to direct me to act upon the defensive strictly, and therefore do not feel at liberty to take a step of the above character until I have received authority to that effect. General Gordon's movements in Florida, resulting in the destruction of Camps Finegan and Milton, were well executed. He effected a perfect surprise.

I have the honor to be, very respectfully and truly, yours,

J. G. FOSTER,

Major-General, Commanding.

Major General H. W. HALLECK.

HEADQUARTERS DEPARTMENT OF THE SOUTH,
Hilton Head, S. C., June 15, 1864.

GENERAL: I have the honor to report that nothing of special interest has transpired in this department since the date of my last report, the 6th instant. The fire upon the city of Charleston has been somewhat increased, and has been continued night and day, at irregular intervals, the number of shots varying from 30 to 60 in ordinary firing. Quite a brisk cannonading was maintained between our batteries and those of the enemy from daylight on the 7th June until noon of the same day. The cause of it was the fire of Fort Putnam (Gregg), which opened upon a small steamer discovered to be aground at daylight on the point of shoal lying between Fort Sumter and Fort Johnson. This was a small steamer used to ply about the harbor and carry supplies to the different forts, and had evidently run aground the night before in returning from Sumter. As soon as Fort Putnam opened upon the rebel steamer the enemy's batteries opened upon Putnam, to which fire our other batteries, including Fort Strong (Wagner), replied. The result was that the rebel steamer was knocked to pieces, upon seeing which the rebel batteries ceased firing and our batteries did likewise.

Four deserters from the Second South Carolina Artillery deserted from Sullivan's Island last week and came within our lines. Eighteen deserters from Savannah came to Fort Pulaski on the 12th. From the information given by these men it appears that the enemy's force at Charleston is 5,000 and at Savannah 2,000, making 7,000 in all, besides the militia.

I am commencing the instruction of the colored regiments in tactics at Beaufort. They are deficient in drill as well as int he firing.