Fort Pulaski is a brick work of five sides of faces, including the gorge, caseated on all sides, walls 7 1/2 feet a thick and 25 feet above high water, mounting one tier of guns in embrasures and one en barbette. The gorge is covered by an earthen outwork (demi-lune) of bold relief.

The main work and demi-lune are both surrounded and separated by a wet ditch. Around the main work the ditch is 48 feet wide; around the demi-lune, 32 feet.

The communication with the exterior is through the gorge into the demi-lune over a draw-bridge, and then through one face of the demi-lune over the demi-lune ditch by another draw-bridge. The scarp of the demi-lune and the entire counterscarp of main work and demi-lune are rivetted with good brick masonry.

At the time of the siege of contained 48 guns, of which 20 bore upon the batteries on Tybee, viz, five 10-inch columbiads, five 8-inch columbiads, four 32-pounders, one 24-pounder Blakely rifle, two 12-inch and three 10-inch sea-coast mortars. A full armament for the work would be 140 guns.

On the 29th of November I was directed by General Sherman to make an examination of Tybee Island and Fort Pulaski, and to report upon the propriety of occupying and holding that island and upon the practicability (and, if deemed practicable, the best method) of reducing Fort Pulaski. I reported as follows:

HEADQUARTERS CHIEF ENGINEER'S OFFICE,
Hilton Head, S. C., December 1, 1861.

Brigadier General THOMAS W. SHERMAN,

Commanding Expeditionary Corps, Hilton Head, S. C.:

SIR: Agreeably to your orders, I proceeded in the steamer Ben DeFord, on the afternoon of the 29th ultimo, to Tybee Island, to make a military reconnaissance of that locality. The enemy had a battery on Warsaw Sound, whose exact position was unknown. The exact position of the battery controlling Warsaw Inlet has no bearing on the prominent points to which my attention was directed, namely, the propriety of occupying and holding the first Tybee Island and the practicability (and, if deemed practicable, the best method) or reducing Fort Pulaski. I deemed the reduction of that work practicable by batteries of mortars and rifled guns established on Tybee Island. I think it probable that a nearer position, on firm ground (although very shallow, and therefore ill-adapted to mortars and sunken batteries), can be found on the island west of Tybee. I would establish these batteries from 20 to 25 yards apart, one gun or one mortar in each, behind the ridge of sand on the shore westward from the light-house. I would sink the mortar batteries as low as the water would permit, and the guns sufficiently low to leave high parapet in front. On the sides and rear of each I would have a high mound of earth, and I would cover each with a horizontal bomb-proof shelter of logs covered with earth and supported by logs planted vertically in the ground. The embrasures for the guns should be deep, narrow, and of very little splay. I estimate that, after once obtaining the range, five-eighths of the shells from the mortars can be lodged inside the fort. I would have enough mortars to throw one shell a minute into the fort, and as many guns as mortars. For landing the ordnance required I would have built two or three large flat-bottomed bateaux or scows, such as are commonly used on rope ferries. I think these could be built here.

There are now probably at Fort Pulaski 700 good troops. About 200 landed yesterday, and the Navy officers informed me that at least 500 have entered the fort within the last three days, while some (probably raw recruits or portions of the Home Guards) have gone away. It may be their design to land on Tybee and hold the west end of it, to prevent the erection of batteries against the fort. I therefore recommend the immediate occupation of Tybee Island by one good regiment until the question of attempting the reduction of Fort Pulaski be determined.

I learned while at Tybee that offers have been made by negroes to burn two of the principal bridges on the railroad between Charleston and Savannah. One of these bridges is said to be nearly 2 miles long. In a military point of view its destruction would be of great value to us, and I recommend the subject to your attention.

Very respectfully, your obedient servant,

Q. A. GILLMORE,

Captain, and Chief Engineer Expeditionary Corps.