COAST DEFENSE, systematic protection of a country against hostile attack along its coast-lines. The term should not be confused with Coast Defenses, which implies only those works erected at special points, for the de fense of limited sections of the coast. In pro viding such defense a nation will consider not only the safety of its territory, but also the se curity of its commercial interests. In any sys tem of coast defense a good navy is the most important feature; and so essential is it con sidered, that all other means are regarded as adjuncts or auxiliaries of the navy. Along a well-defended coast, in suitable places, are sta tions or points of support where is stored the requisite material for building, equipping, re pairing and supplying naval vessels, and where provision is made for furnishing men when ad ditional force is needed. Forts are built in places where the coast artillery may co-operate with the navy in obstructing the advance of an enemy intending to capture a city or to invade the country; where their guns may command the entrance to a harbor or other approach by water; wherever they may cripple the enemy's attack on the defensive fleet, leaving it free to attack the enemy in turn; where forts may as sist each other and co-operate in repelling an invasion or preventing a blockade or a bom bardment; where minor channels of approach may be closed or guarded, thus enabling the navy to give entire attention to the main chan nel, etc. Torpedo-boats, submarines, harbor mines, the searchlight, which illuminates the harbor and permits detection of the enemy's manoeuvres, and hydroplanes, are all valuable aids for the forts. The unfortified coast, as well as the land approaches to cities, must be defended in time of war by whatever means are at command.
The guns for coast defense change with the places and purposes for which they are to be used. To pierce the side armor of battleships, the flat trajectory, high-power guns are used; for projectiles intended to fall on the decks of an enemy's ships, the high-angle guns (mortars or howitzers) are employed. The number and size of guns vary with the estimated number and calibres of those which may be brought to bear by an enemy. From the depth and length
of the channel may be determined how many and what classes of ships the enemy can oper ate in it, their armament, etc., and from these data the number and calibres of guns needed may be calculated.
The difficulty of obtaining naval supplies after war has been declared makes it necessary to store them during times of peace. Besides quantities of supplies at points of support for the navy, important harbors are generally equipped with torpedo storehouses, cable-tanks, mining casements, etc., for use in emergencies.
The tactics of coast defense have changed greatly since the beginning of the last decade of the 19th century. Besides defense against attack upon fortified places preparation is also necessary for resisting assaults upon unforti fied coasts. The length of the United States coast-line makes its secure fortification a mat ter of great difficulty and expense.
Methods of reconnaissance are important for defense as well as for attack. The defense seeks to veil all batteries, and even in times of peace a journey along a fortified coast might not discover many forts or other means of de fense. The enemy, in preparation for attack, or in action, seeks to discover the natureaii strength of the defenses; and the defense in turn uses all possible methods of ascertaining the number and classes of the enemy's ships, the probable line of attack and whatever else may be discoverable in regard to his strength and purposes. Pictures of every important warship in the world are studied by certain officers of every navy and so dose are some of these stuches that a war vessel may be recogruzed by such an officer in any position in which he sees it. For the important work of reconnais sance, observation stations are fully equipped for the coast artillery, photographs, drawings, de scriptions of warships, telescopes, etc., for use in procuring information of the enemy, being fully provided. One of the chief means of observation is the aeroplane or hydroplane.