every direction. No openings should be made except for communication or for embrasures. When guns are mounted upon elevated platforms, the same degree of safety should be aimed at by mans of traverses.
2. The next important point, and especially when exposed to bombardments, is the erection of bomb-proofs in convenient proximity to each battery; these to be constructed of substantial timbers about a foot square, covered with masses of earth, giving a thickness of not less than 14 feet, unless the soil be entirely of sand, when 12 feet, well compacted, will answer. Each bomb-proof should be provided with free ventilation, which can be secured by making several entrances in directions not exposed to shot, and by flues passing through the superincumbent earth, constructed with elbows to guard against chance shot falling through.
3. In regard to the outer line of defense for Mobile, I would say that I consider the arrangements as described by you generally good; but I do not consider the counterscar gallery as the best flanking arrangement, the objection being inconvenience of communicating with it from the interior of the battery.
Your proposed plan for flanking the space between the bomb-proof and the parrapet I think good, and if kitchens, surgeon's room, and sinks can be introduced, as suggested by you, it will be judicious to construct them.
4. When parapets are exposed to batteries of heavy guns, particularly the rifle gun, we are giving them a thickness of not less than 25 feet; against field artillery, 18 or 20 feet will suffice. If possible, you should collect a good supply of sand-bags, to be kept in store, to be used during the siege in the construction of merlons and revetments generally.
5. You mention that General Lee Leadbetter dispenses with heberme at the foot of his exterior slopes, the object being, I suppose, to make it more difficult for the enemy to scale the works. This change in the ordinary profile I consider unfortunate, as it will ten to make the parapets less stable, and involve much labor in constant repairs. Experience in this war has shown that the Federal troops are not inclined to storm intrenchments. Therefore, in their construction we should look more particularly to their capacity to resist heavy shot, and to their durability, rather than to the form or profile best against assault.
6. If time and labor can be had, I consider it important that the batteries of your outer line should be connected by a continuous work of infantry cover, or rifle-pits, taking care that they be not exposed to an enfiladed fire from the batteries in the harbor or from points exterior to your works. When an enfilading fire cannot be avoided in any other way, a few traverses at right angles to the parapet, at proper intervals, will afford much protection. The thickness given to traverses should be as great as that of the parapets, and for their better protection it will be advisable in many cases to raise them several feet higher than the interior crest. In some cases traverses and bomb-proofs can be combined with advantage, and, for the sake of economy, this method should be resorted to when practicable. Magazines may also be introduced at times with great saving of labor.
The sketch of your works which you refer to in your letter was not received, which I regret, as this letter could have been written more satisfactorily had it been before me.
In the further prosecution of work, the plans decided upon by General Leadbetter will, as a rule, be adhered to, but should modifications