COAST DEFENSE. The defense of a sea coast inrolves the principles of both strategy and tactics. In considering the principles of strategy applicable to coast fortification it is essential to take into account the navy as our first line of de fense. Every nation possessing a coast line has commercial interests, to protect which she re quires a navy. Her fleet., whatever its strength, will require points of support on the home coast, to sere as a basis of operation in attack or defer se. These points of support contain all the material necessary for building or equipping ships; they furnish all the needed men and sup plies to the navy, and must offer for a beaten fleet, or one which on the outbreak of war has not yet completed its equipment, a safe harbor to repair damages or complete equipment. The material of a navy is very expensive and is diffi cult or impossible to secure after war has begun; consequently, the greater part must be prepared in time of peace and collected at the points of support, for which purpose extensive depots, magazines. and other constructions must be erect ed. To prevent all these constructions from be ing demolished at one blow, and to guard the fleet, while still taking in supplies or completing its equipment, against surprise, these points of support must be protected by suitable means, and this is the purpose of fortifications.
The only points of a coast that fulfill the con ditions imposed by these considerations are the larger harbors (always bays and mouths of rivers), and they must be fortified not only against attack by sea, but also against land at tack, for the late war between .Japan and China showed conclusively that important naval ports (Port Arthur and Wei-hai-wei. for example) may he taken by forces landed on the coast without risking an attack on them by sea.
In applying the principles of land tactics to the selection of sites for, and the construction of, sea coast forts, some modifications must be introduced, due to the fact that the enemy in the latter case is confined to the navigable channels, so that all his possible flanking attempts can be foreseen and provided against. The principles of tactics which find application here are: (1) To obstruct the enemy's advance, while leaving free that of the forces of the defense for offensive movements; in other words, so to obstruct the water ap proaches against the enemy as to leave free en trance and exit for the defending fleet. (2) To be superior to the enemy at the point of attaek; that is, to bring to bear on the channels of ap proach a heavier fire of high-power guns and how itzers and mortars than any fleet able to operate there can bring to bear on the defenses. (3) To place the isolated units for most effective action so as to be mutually supporting: this is accom plished by scattering the forts to prevent the en emy from concentrating his fire, at the same time arranging them so that fire can he concentrated on him. (4) 'l'o protect well the flanks of the posi tion and compel the enemy, if he attacks at all, to make a direct frontal attack. This is done by closing all unnecessary channels, by protecting the obstructions by means of rapid-firing guns and the operators by means of hombproofs, and at night by illuminating the obstructed field with search-lights. (5) To provide means for offensive
returns against countermining operations, either by means of a swarm of torpedo-boats, or by bat teries for operating movable torpedoes from the shore.
There are two systems of guns in use in coast artillery: the flat trajectory, high-power guns, designed to pierce the side armor of battle-ships, and the high angle pieces (howitzers or mortars) whose projectiles are designed to fall On the decks. Both are necessary, and each has its proper sphere of action, the former having by far the greater accuracy, and the latter attacking the battle-ship at its weakest point. In Europe how itzers are generally preferred; but the recent tests of mortars near Portland, Maine, have proved the greater value of the latter. The calibre of the fort gulls must be at least equal to that which the depth of water in the channel will enable the enemy to bring against the defenses and sufficient to pierce his armor at the outer mine field, or at about two-mile range. The greatest thickness of Kruppized steel used in the latest battle-ships is about 12 inches at the belt, and to penetrate this at the required, range will require a 10-inch gun. The average thickness of deck armor most in use at present is about :3 inches of hardened nickel steel, and to penetrate this a high-angle gun (howitzer or mortar) 12 inches in calibre will be required. These, then, are the maximum calibres required against battle-ships, but to prevent dis tant bombardment of cities, etc., there is a 12-inch rifle and for close ranges also an 8-inch rifle. Armored cruisers have from 5 to 6 inches of hard ened nickel-steel armor, and to penetrate their armor within the mine field (where they first come seriously into play) will require a 5-inch or 5-inch rapid-fire gun. The smaller vessels have but little armor protection, hut as they come into action at the outer mine field (about 3330 yards) the smaller calibre guns to fight them must have the necessary penetration at that range, conse quently must he about 2.5 to 3 inches in calibre.
The number of gulls of each calibre should be at least half of, and preferably equal to, those the enemy call bring to bear. The latter is deter mined by noting on the map the length of channel (within three miles of the fort considered) which the enemy's fleet can occupy, and allowing from five to ten ships to the mile. From the depth of channel the ships of the enemy which can go there can be determined, and from their armor and armament the kind and number of gulls required. If the enemy's armament is not known, then in deep channels from 30 to 60 guns of 6-inch calibre And over most be allowed to the mile (Abbot).
The outer mine line is derived by the intersection of the curves representing the limit of armo• piercing ranges of the guns on either side of the i.ntra lo that these torpedoes are under the effective fire of all the guns in the harbor; the inner line is usually at the narrowest part of the entrance.
The battle tactics of coast defense comprise de lense against blockade, bombardment, and attack by sea.