The entrance from the Gulf was guarded by two works, Fort Morgan on Mobile Point and Fort Gaines on Dauphin Island. The approach by Mississippi Sound was covered by Fort Powell, a small earthwork on Tower Island, commanding the channel which gave the most water, known as Grant's Pass. Gaines was too far distant from the main ship channel to count for much in the plans of the fleet. It was a pentagonal work mounting in barbette[22] three X-inch columbiads, five 32-, two 24-, and two 18-pounder smooth-bore guns, and four rifled 32-pounders; besides these it had eleven 24-pounder howitzers, siege and for flank defence. In Fort Powell there were[23] one X-inch, two VII-inch and one 32-pounder smooth-bore and two VII-inch Brooke rifles; these bore on the sound and channels, but the rear of the fort toward the bay was yet unfinished and nearly unarmed. The third and principal work, Fort Morgan, was much more formidable. It was five sided, and built to carry guns both in barbette and casemates; but when seized by the Confederates the embrasures of the curtains facing the channel were masked and a heavy exterior water battery was thrown up before the northwest curtain. The armament at this time cannot be given with absolute certainty.[24] The official reports of the United States engineer and ordnance officers, made after the surrender, differ materially, but from a comparison between them and other statements the following estimate has been made: Main fort seven X-inch, three VIII-inch and twenty-two 32-pounder smooth-bore guns,[25] and two VIII-inch, two 6.5-inch and four 5.82-inch rifles.[26] In the water battery there were four X-inch and one VIII-inch columbiads and two 6.5-inch rifles.[27] Of the above, ten X-inch, three VIII-inch, sixteen 32-pounders and all the rifles, except one of 5.82 calibre, bore upon the channel. There were also twenty flanking 24-pounder howitzers and two or three light rifles, which were useless against the fleet from their position.
Such were the shore defences. In the waters of the bay there was a little Confederate squadron under Admiral Franklin Buchanan, made up of the ram Tennessee and three small paddle-wheel gunboats, the Morgan, Gaines, and Selma, commanded respectively by Commander George W. Harrison, and Lieutenants J.W. Bennett and P.U. Murphy. They were unarmored, excepting around the boilers. The Selma was an open-deck river steamer with heavy hog frames; the two others had been built for the Confederate Government, but were poorly put together. The batteries were: Morgan, two VII-inch rifles and four 32-pounders; Gaines, one VIII-inch rifle and five 32-pounders; Selma, one VI-inch rifle, two IX-inch, and one VIII-inch smooth-bore shell-guns. Though these lightly built vessels played a very important part for some minutes, and from a favorable position did much harm to the Union fleet in the subsequent engagement, they counted for nothing in the calculations of Farragut. There were besides these a few other so-called ironclads near the city; but they took no part in the fight in the bay, and little, if any, in the operations before the fall of Mobile itself in the spring of 1865.
The Tennessee was different. This was the most powerful ironclad built, from the keel up, by the Confederacy, and both the energy shown in overcoming difficulties and the workmanship put upon her were most creditable to her builders. The work was begun at Selma, on the Alabama River, one hundred and fifty miles from Mobile, in the spring of 1863, when the timber was yet standing in the forests, and much of what was to be her plating was still ore in the mines. The hull was launched the following winter and towed to Mobile, where the plating had already been sent from the rolling mills of Atlanta.
Her length on deck was 209 feet, beam 48 feet, and when loaded, with her guns on board, she drew 14 feet. The battery was carried in a casemate, equidistant from the bow and stern, whose inside dimensions were 79 feet in length by 29 feet in width. The framing was of yellow pine beams, 13 inches thick, placed close together vertically and planked on the outside, first with 5½ inches of yellow pine, laid horizontally, and then 4 inches of oak laid up and down. Both sides and ends were inclined at an angle of forty-five degrees, and over the outside planking was placed the armor, 6 inches thick, in thin plates of 2 inches each, on the forward end, and elsewhere 5 inches thick. Within, the yellow pine frames were sheathed with 2½ inches of oak. The plating throughout was fastened with bolts 1¼ inch in diameter, going entirely through and set up with nuts and washers inside. Her gunners were thus sheltered by a thickness of five or six inches of iron, backed by twenty-five inches of wood. The outside deck was plated with two-inch iron. The sides of the casemate, or, as the Confederates called it, the shield, were carried down to two feet below the water-line and then reversed at the same angle, so as to meet the hull again six to seven feet below water. The knuckle thus formed, projecting ten feet beyond the base of the casemate, and apparently filled in solid, afforded a substantial protection from an enemy's prow to the hull, which was not less than eight feet within it. It was covered with four inches of iron, and being continued round the bows, became there a beak or ram. The pilot-house was made by carrying part of the forward end of the shield up three feet higher than the rest. The casemate was covered with heavy iron gratings, through whose holes the smoke could rise freely, and it was pierced with ten ports, three in each end and two on each side. The vessel carried, however, only six guns; one VII-1/8-inch rifle at each end and two VI-inch rifles on each broadside. These were Brooke guns, made in the Confederacy; they threw 110-pound and 90-pound solid shot. The ports were closed with iron sliding shutters, five inches thick; a bad arrangement, as it turned out.
Though thus powerfully built, armored, and armed, the Tennessee must have been a very exasperating vessel to her commander. She had two grave defects; the first, perhaps unavoidable from the slender resources of the Confederacy, was lack of speed. Her engines were not built for her, but taken from a high-pressure river steamboat, and though on her trial trip she realized about eight knots, six seems to be all that could usually be got from her. She was driven by a screw, the shaft being connected by gearing with the engines. The other defect was an oversight, yet a culpable one; her steering chains, instead of being led under her armored deck, were over it, exposed to an enemy's fire. She was therefore a ram that could only by a favorable chance overtake her prey, and was likely at any moment to lose the power of directing her thrust.
Such as she was the Tennessee was ready for service early in March, 1864, when Commander J.D. Johnston was ordered as her captain. She was taken from the city, through one of the arms of the Alabama, to the mud flats which reach to a point twenty miles down the bay, and are called Dog River Bar. The least depth of water to be traversed was nine feet, but throughout the whole distance the fourteen feet necessary to float the vessel could not be counted upon. She was carried over on camels, which are large floats made to fit the hull below the water line, and fastened to it, on either side, by heavy chains passing around them and under the keel, while the camels are filled with water. When the water was pumped out the buoyancy of the camels lifted the ram five feet, reducing her draught enough to let her go over the bar. Two months were taken up in building and placing the camels, during all which time Farragut was begging either for ironclads or for co-operation by the land forces, in reducing the forts. In either case he was willing to enter the bay, but he did not like to run the risk of getting inside with his wooden ships crippled, the forts intact in his rear, and the enemy's ironclads to contend with as well. Neither assistance was given, and he was therefore compelled to look on while the Tennessee was moved from a position in which she could do no harm to one in which she became the principal menace to the attacking fleet. On the 18th of May she was finally towed across and anchored in the lower bay six miles from the entrance. That night the camels were removed, steam raised, and everything made ready to cross the outer bar and attack the fleet; but when the anchor was weighed the ship was found to be hard aground. The intended attack was given up, and when the tide rose enough to float her, she was moved down to Fort Morgan, near which she remained from that time.
The preparations for defence of the enemy were not confined to the forts and the ships. From the point of Dauphin Island a line of pile obstructions extended across the sand bank, in the direction of Fort Morgan, blocking the passage of any light vessels that might try to pass that way. Where the piles ended, near the edge of the bank, a triple line of torpedoes in échelon began, extending across the main ship channel to a red buoy, distant two hundred and twenty-six yards from the water battery under Fort Morgan. This narrow passage, not much exceeding one hundred yards from the beach, was left open for blockade-runners, and through it the admiral intended his fleet to pass; for the reports of refugees and the examinations made by officers of the fleet who dared at night to push their search thus close under the enemy's guns, alike affirmed that there at least no torpedoes were.
The torpedoes planted in this part of the defences of Mobile were principally of two kinds, both of the class known as floating torpedoes. One was made of an ordinary barrel, lager-beer kegs being preferred, pitched inside and out and with wooden cones secured to the two ends to keep it from tumbling over. The barrel was filled with powder and furnished with several, generally five, sensitive primers, placed near together in that part of the bilge which was to float uppermost. The primers were exploded by a vessel striking them and communicated their flame to the charge. The other torpedo was made of tin, in the form of a truncated cone, the upper diameter being the greater. It was divided into two parts, the upper being an air-chamber and the lower containing the charge. On top was a cast-iron cap so secured that a slight blow, like that from a passing vessel, would knock it off. The cap was fast to a trigger, and as it fell, its weight pulled the trigger and exploded the charge. In July, 1864, there were planted forty-six of the former and one hundred and thirty-four of the latter kind. Besides these which exploded on contact there are said to have been several electrical torpedoes.
The first six months of 1864 wore away in the monotonous routine of the blockade, broken only by an attack upon Fort Powell, made from Mississippi Sound by the admiral with the light-draught vessels. These could not get nearer than four thousand yards, but at the time, February 28th, Sherman was on his raid into Mississippi and the attack was believed to be of service as a diversion. During this half of the year none but wooden vessels lay before Mobile. Toward the end of July the co-operation of Canby's forces was assured and the monitor ironclads began to arrive.
The root idea from which the monitor type of ironclads grew was a raft carrying a fort; their hulls, therefore, floated low in the water, the deck being but a foot or two above it. Upon the deck were one or more circular turrets, made of one-inch rolled wrought-iron plates, the whole thickness depending upon the number of these thin plates bolted together. The decks, and the hulls to some distance below the water-line, were also armored, but less heavily. In the turret two guns were mounted, of a size varying with the size of the vessel. They could be moved in and out, but the aim from side to side was changed by turning the whole turret, which revolved on a central spindle. After firing, the ports were turned away from the enemy and the unbroken iron toward him, until the guns were reloaded. Above and concentric with the turret was another circular structure, of much less diameter and similarly armored. This, called the pilot-house, contained the steering-wheel, and was the station in battle of the captain, helmsman, and pilot if there were one. It was stationary, not sharing the revolving motion of the gun-turret, and could be entered only by a hole opening down into the latter, the top being closed by iron plates, which had been given greater thickness since a shot in one instance had struck and broken them, killing the captain of the vessel. Narrow horizontal slits were cut in the armor of the pilot-house, through which the captain peered, as through the bars of a helmet, to see his enemy and direct the course of his ship. The gun-turret could be entered or left by the hull below, which contained the living rooms of the officers and crew and all the usual and necessary arrangements of a ship of war, or by the gun-ports, which were large enough for a man to pass through. In action the hatches were down, and ordinarily the only exit from the hull below was through the turret and its ports. Four of these vessels were sent to Farragut after many askings and months of delay; two from the Atlantic coast, the Tecumseh and Manhattan, having ten-inch armor on their turrets, and two from the Mississippi River, the Chickasaw and Winnebago, with eight-and-a-half-inch armor. The former carried two XV-inch guns in one turret; the latter four XI-inch guns in two turrets. They were all screw ships, but the exigencies of the Mississippi service calling for light draught, those built for it had four screws of small diameter, two on each quarter. The speed of the monitors was poor and, as they had iron hulls, varied much as their bottoms were clean or foul. From a comparison of differing statements it may be taken at from five to seven knots.