The ground immediately around Fort Saint Philip is as high, or rather higher, than that about Fort Jackson.
There is quite a large triangular space of high ground between the river and Bayou Mardi Gras (just below the fort), and thence extending along the river and bayou banks. The limit of hardest ground passes about a hundred yards behind the rearmost salient of the fort.
It is called by Lieutenant Smith (who surveyed it) "practicable for infantry, cavalry, or artillery." For several hundred yards farther back indeed the ground is passable for footmen, but would be found pretty soft and miry in wet weather though still supporting footmen.
The banks of the Bayou Mardi Gras are pretty high and firm half way at least to the Gulf; the bayou itself, though narrow, has 10 to 15 feet water in it except over its bar. Lime kiln Bayou has much the same character. the external waters of the Gulf are shoal, and I presume nothing can approach the mouths of these bayous except boats.
With these preliminaries I will my ideas about the attack. I should consider necessary, first, a powerful fleet, bearing from 300 to 400 guns (as many 11 and 9 inch guns as can be had). Second, half a dozen iron-clad gunboats (or as many more as can be had). Third, 10,000 troops. (All these might not be necessary in reducing the works, but they should be with the expedition, to take immediate advantage of its success.)
I should hope to reduce the works without regular siege operations; but even if it became necessary to resort to them, the powerful artillery of the fleet would make a large siege train unnecessary, I should judge that a dozen 24-pounder siege guns, a dozen 10-inch siege mortars, and as many field guns (these to be furnished from dismounted batteries attacked to the division of troops) would suffice and the fleet should be accompanied by say fifteen or twenty mortar vessels, such as are now being equipped.
The difficulties of regular approaches against these works and the advantages likely to be derived from prompt and bold measures, which may overwhelm the works before the defenders can get time to accustom themselves to a state of siege, are so great that I shall not suggest as a preliminary attack any land batteries. Doubtless if it was in the month of November or December it would be an important step to land troops below, surround Fort Jackson by skirmishers (taking advantage of the leaves), and to establish batteries enfilanding all the water batteries of this work bearing across and down the river. During the high-water reason I doubt the practicability of this, and whether practicable or not, believe that the measure would not justify the discouragements and delays arising.
The plan I would suggest would be based upon the fact that the batteries of the forts are all, except sixteen guns of Fort Jackson, en barbette; that they are all very low; that they can be approached to within 200 yards, and moreover that, while Fort Jackson is a very strong work, Fort Saint Philip is comparatively weak, and can scarcely be considered as secure against a coup de main, and that Fort Saint Philip once fallen into our possession, its own batteries enfiladed or taken in reserve, all the downstream-bearing barbette batteries of Fort Jackson, and that from a point 200 or 300 yards below Fort Saint Philip the remaining barbette batteries of Fort Jackson can be enfiladed and the scarps of the two water fronts breached. From a point marked C, 600 yards from the uppermost batteries of Fort Jackson, to a point marked D, 600 from the lower batteries, is a distance of about 1,600 yards. Along this line I presume twelve vessels can be laid without danger of fouling, and if