chassis, the barbette wheels strike against the scarp walls, and materially interfere with pointing the guns, and intercept their full elevation in consequence.
But taking the 9-inch Dahlgren gun, however, the best gun, with full charge and elevation, its extreme range falls short of Cat Island about a mile and a half. Within this mile and a half of the channel, I am informed by pilots familiar with the sound, there is 18 feet of water. Hence, admitting that the fortification is completely defensible within itself and mounted with the best guns, yet nevertheless it could not prevent the passage of large-class ships through the very channel which it is built to guard. This, however, is but one passage leading into the sound.
Between Ship and Horn Islands there is another, with a depth of 14 feet of water, and between the eastern and of Horn Island and Petit Bois still a third, which several pilots agree in stating had deepen to 18-feet during the heavy storms of last year.
Now, the coast line is about 15 miles distant from these island keys, which partly lock and protect the main-land. About midway between them, a line drawn from east to west and generally parallel with the coast, will represent the 13-foot line of water, and from this line to the main-land the water shoals very rapidly, becoming extremely shallow as the coast line is approached.
It is hence evident that gunboats of light draught can alone be used by the enemy against the coast. Upon this coast there are only two points of so much consequence as to require a vigilant guard. These are, 1st, New Orleans, though the Rigolets, and, 2nd, Mobile, through Dog and Pascagoula Rivers; for, if the war is to be prosecuted by the enemy regardless of all the rules governing civilized communications, it will be utterly impracticable without a navy to protect all the watering places and residences along the sound, and indemnity must be looked for either by the confiscation of Northern property within our borders or by a like retaliation across them.
But with the cities mentioned the case is different, as their possession by the enemy may change the destinies of the war. Through Dog and Pascagoula Rivers light transports and gunboats can pass to within 20 or 25 miles of Mobile, thus throwing men and material to within a single day's march of that city, with fair roads leading thence through an open pine country. A few batteries erect at suitable points on those rivers can prevent this, and the guns used need only be of the caliber of 24 or 32 pounders.
In a like manner Fort Pike, on the Rigolets, can be strengthened and one or two other points fortified, which will prevent an entrance into Lake Pontchartrain. If the enemy obtains possession of Fort Pike, and thus a foothold on the lake, by operating thence as a base with the boats and material to be collected upon its shores, the capture of New Orleans becomes almost certain in time, and consequently Forts Jackson and Saint Philip and the control of the entire mouth of the Mississippi River, by starving those forts into capitulation.
The occupation of Ship Island even by the most powerful fortifications, fully capable of resisting a combined land and naval attack, does not benefit either of the two important points mentioned, nor yet protect them in the least. Neither does it protect the sound coast, as gunboats can pass between Ship Island and the main-land with impunity, passing thereto through any of the channels in and around the islands.
Nothing, for instance, would be more easy for the enemy than the capture of the small steamers and other craft now plying in the sound