COAST DEFENCE. The term coast defence is sometimes liable to be confused with what is really local defence. It is now accepted that it is not possible to defend the whole length of a coast line of even a comparatively small country like Britain from spasmodic assaults by sea. It is quite possible, however, with an adequate Navy, to give security against invasion or prolonged attack.
Aerial bombardments on a large scale are an entirely separate problem (see AIR WARFARE) and their antidote does not come under this heading.
General Principles.—Stated briefly, the only true defence of a country's coast line against attacks from the sea, is a fleet, which, under modern conditions, means a force consisting of battleships, carriers, cruisers, destroyers, submarines and aircraft ; and that fleet must be free to move out and give battle to the enemy in the open sea, and not be tied to any particular locality, however important it may seem.
This important principle was not always recognized in the past and there are numerous historical instances of the misuse or lack of understanding of sea power by rulers or even great military commanders. As an example of this defect in the outlook and training of those responsible for the conduct of war, we may note how, in 1588 Queen Elizabeth's Privy Council rejected Drake's plan to mass the available ships into a single great fleet to meet the Spanish Armada before it could approach home waters. To the English Government Parma's army in the Netherlands seemed so serious a menace as to necessitate the retention of an Eastern squadron in the Strait of Dover. They failed to perceive that an army on the mainland would be impotent to invade England unless a safe passage was assured by the presence of a fleet which had already met and defeated the enemy fleet, or had effectively ex pelled it from the waters to be traversed. As it was, the English naval forces were divided and the western fleet was nearly caught at grave disadvantage in the port of Plymouth. Good tactics, fine seamanship and superior gunnery, redeemed faulty strategy; the Armada was defeated and dispersed; Parma's army never em barked.
At a later date we see the fleet itself suffering owing to the prevalence of a faulty doctrine that it was possible to defend the country against attack from the sea, by isolated naval units. About 1870 the British Admiralty was building coast defence ships of very low sea-going and fighting efficiency. These were dotted round the coast of England and at one or two naval bases abroad. They gave an entirely false sense of security to the local inhabit ants if not to the country at large. Actually this constituted a typical example of that dispersal of strength which is anathema to the sound strategist. The same false ideas were manifest in the Spanish-American war, when the inhabitants of some of the American sea ports clamoured for guardships.
United States.—The term coast defence, as used in America, is understood to mean systematic protection against hostile attack along coast lines. The great length of the United States coast line makes it both difficult and expensive to secure adequate forti fication. In the United States the army and the navy are jointly responsible for coast defence, and operations are carried out under a chief of staff with the Secretary of the Navy at the head of the department. The authorized strength of the Coast Artillery Corps of the Army at the close of 1925 was 14,42o enlisted men and i ,000 officers.
The progress of the work of providing armament for the ex posed harbours has been contingent upon congressional appro priations. Great impetus was given the work when public attention was focused upon the grossly inadequate defences existing at the outbreak of the Spanish-American War. Construction was then begun and has since been carried forward on implements, fortifica tions, guns, mortars, gun-carriages, special ammunition, smokeless powder, high velocity explosives, the development of rapid fire and fire control.
By 1915 all ports of commercial and strategic importance had been fortified with the exception of the entrance to Chesapeake Bay. The fortification of the Panama Canal (q.v.) on both sides has been completed and similar work is in progress in all outlying possessions. The present policy of armament of the government calls for the installation for defence of at least one 16-inch gun in or near every harbour.
The modern method of emplacement is to spread the guns over a considerable area, and to have them connected by supply and control lines. Such an arrangement makes destruction by an attacking fleet almost impossible and adds to the difficulty of land operations by an enemy. A large number of American guns are mounted on disappearing carriages where they are completely concealed from lateral view. The use of aeroplanes in reconnais sance and direction of offensive and defensive action has modified the designs of new coast works and it is believed that in the future many of the guns, large and small, will be mounted on rails and moved to constantly changing positions. In July, 1929, experi ments in the United States with a large calibre gun mounted on a truck, hauled by railroads parallel to the coast line, were highly successful, and it is believed plans for the complete mobilization of coast defence may be feasible.
A very striking contrast between the influence of sea power and of shore defences in guarding a coast was afforded during the World War. The German army, having forced its way to the Bel gian coast, found that their navy could not afford adequate protec tion to its right flank against attack from the sea. So there grew up along the miles of coastline between Nieuport Canal, where that flank rested, and the Dutch frontier, the most tremendous system of batteries and other coast defences the world has ever seen, including over three hundred guns, six inch and above.
On the other side of the canal the left flank of the French and Belgian armies also rested on the sea, but the coast behind them was innocent of any sizeable battery which could fire to seaward as far back as Dunkirk, and even this historic fortress relied on a comparatively antiquated armament. Here, however, was the base of a considerable naval force, mostly British, which, throughout the war, effectually safeguarded this section of the coast.
In spite of the array of shore defences on the German side, their coastline and harbours in Belgium were assaulted by heavy bom bardments, numerous torpedo attacks and the famous landing and blocking expeditions against Zeebrugge and Ostend (see BELGIAN COAST OPERATIONS).
When the problem of Coast Defence is expanded into that of safeguarding a number of widely scattered territories like those composing the British Empire, the whole question of the disposi tion and allocation of armed forces assumes a much broader aspect. The policy to be adopted must depend largely on international re lations and is liable to vary to some extent from time to time ac cording to the distribution of foreign armed forces, particularly those of a naval character. (See NAVY.) Local Defence.—In spite of the fact that to attempt to render inviolate a whole length of coast line will generally be mere waste of effort, the defence of particular localities, such as large commer cial ports or naval bases, may often be essential. Such local de fence must necessarily vary with geographical and other condi tions, but will generally necessitate a combination of sea, land and air forces. These, in turn, will be effective only if they are either adequate in themselves to meet the largest scale of attack which may be launched against them or if they can hold out until rein forced. Even so, it can seldom if ever be guaranteed that a place will be absolutely secure from any and every form of attack. The best that can be sought for is to make the risks incurred by an enemy so great as to render attack improbable.
All the chief sea Powers have adopted the principle of establish. ing some form of permanent defences at their more important naval bases. In some cases large ports, mainly commercial in char acter, also have fixed defences. On the other hand, there is a grow ing disinclination to expend large sums on fortresses and immobile defences generally and an increasing tendency to rely on more mo bile forms of defence, such as submarines, auxiliary surface war ships including minelayers, and aircraft.
It cannot be said, however, that the coast defence battery is ob solete. Mobile defences such as the foregoing may be eluded or may be affected by bad weather, when, but for the fixed defences, the locality would be at the enemy's mercy. Broadly speaking, the principle is to provide the minimum permanent defences consistent with the importance of the place to be defended and having regard to its distance from a potential enemy on the one hand, and rein forcements on the other.
It is possible that as air power increases in range, intensity and reliability, it may be found possible to reduce permanent defences still further, but, at present, the aeroplane is not a complete and efficient substitute for the heavy, long-range fortress gun ; still less can it replace those naval units which are an essential part of any system of local defence against sea attack. (E. A.) Technical.—Attacks on defended harbours or anchorages may be from the sea, air or land, and these may be simultaneous. At tack from the land by itself will not be considered here, but his tory shows that this has proved the most successful method, e.g., Sebastopol, Port Arthur, Tsingtao, and its menace must influence the local defence scheme.