ENGINEER BUREAU, Richmond, April 6, 1863.

Major D. B. HARRIS,

Corps of Engineers, Charleston, S. C.:

MAJOR: I have the acknowledge receipt of your letters of 27th and 29th ultimo, the former transmitting a copy of Captain McCrady's report upont the defensive works in the District of Georgia, and the wants of the engineer service, and suggesting wherein its efficiency may be increased; the latter inclosing a statement of the present armament of the works around Savannah.

I notice in Captain McCrady's report of the 26th January last that he states, after describing the obstructions placed in the Savannah River at the head of Elba Island, that-

The obstructions would be in every respect satisfactory were it not for the two following objections:

1st. That it is an average distance of 1 1/4 miles from the river battery.

2nd. That the west end of Elba Island interposes between the obstructions of the main Ship Channel and that of the South Channel.

For reasons given Captain McCrady is of the opinion that the distance named (1 1/4 miles) renders the river batteries incapable of preventing the enemy from getting possession of the obstructions, and that Elba Island affords additional advantages to the enemy.

Cannot this error in the relative locations of batteries and obstructions be remedied in part by constructing good shelter for sharpshooters at points below the batteries and within good range of the obstructions? Again, why not build a battery nearer the obstructions and transfer to it a part of the guns now mounted in the existing ones? The ground is all of the same level, and it is presumed the change of locality could be made without impairing the efficiency of the guns in firing upon the approaches of the enemy. Covered communications between the batteries and any advanced shelters for sharpshooters should be established. From the existing state of things, Captain McCrady says, "results the necessity of an interior line of obstructions nearer the city."

I must request you to give this point your special consideration before authorizing the construction of an interior line of obstructions. The air-line distance from Fort Jackson to the Exchange building in the city of Savannah is 3 miles, and to the eastern suburbs only 2 1/2 miles. Long-range guns, therefore, fired from an iron-clad in the river opposite Fort Jackson will throw projectiles into the city, and without ascending to the line proposed for the interior obstructions the enemy can destroy one-half of the place.

Will the second obstruction, therefore, be of any advantage? They certainly cannot protect Savannah against a bombardment at long range.

I have been urging the importance of sending the heavy guns wanted at Savannah, but up to this time the Ordnance Department has not responded, and for the reason, as I am informed, that urgent calls are made for all the guns the can be manufactured to be sent to other vital points. I have again pressed the matter upon the Chief of Ordnance with the hope that a part of the requisition made by General Beauregard in November last may be still supplied. Steps have been taken by this bureau to import instruments, intrenching tolls, and stationery for the use of the engineer service. Should they prove unsuccessful the establishment of shops for the manufacture of implements will become a necessity.