1911 Encyclopædia Britannica/Coast Defence

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COAST DEFENCE, a general term for the military and naval protection and defence of a coast-line, harbours, dockyards, coaling-stations, &c., against serious attack by a strong naval force of the enemy, bombardment, torpedo boat or destroyer raids, hostile landing parties, or invasion by a large or small army. The principal means employed by the defender to cope with these and other forms of attack which may be expected in time of war or political crisis are described below. See also for further details Navy; Army; Fortification and Siege-craft; Ammunition; Ordnance; Submarine Mines; Torpedo. The following is a general description of modern coast defences as applied in the British service.

No system of coast defence is of any value which does not take full account of the general distribution of sea-power and the resultant strength of the possible hostile forces. By resultant strength is meant the balance of one side over the other, for it is now generally regarded as an axiom that two opposing fleets must make their main effort in seeking one another, and that the force available for attack on coast defences will be either composed of such ships as can be spared from the main engagement, or the remnant of the hostile fleet after it has been victorious in a general action.

Coast defences are thus the complement and to some extent the measure of naval strength. It is often assumed that this principle was neglected in the large scheme of fortification associated in England with the name of Lord Palmerston, but it is at least arguable that the engineers responsible for the details of this scheme were dependent then as now on the naval view of what was a suitable naval strength. Public opinion has since been educated to a better appreciation of the necessity for a strong navy, and, as the British navy has increased, the scale of coast defences required has necessarily waned. Such a change of opinion is always gradual, and it is difficult to name an exact date on which it may be said that modern coast defence, as practised by British engineers, first began.

An approximation may, however, be made by taking the bombardment of Alexandria (1881) as being the parting of the ways between the old and the modern school. At that time the British navy, and in fact all other navies, had not really emerged from the stage of the wooden battleships. Guns were still muzzle-loaders, arranged mainly in broadsides, and protected by heavy armour; sails were still used as means of propulsion; torpedoes, net defence, signalling, and search-lights quite undeveloped.

At this time coast defences bore a close resemblance to the ships—the guns were muzzle-loaders, arranged in long batteries like a broadside, often in two tiers. The improvement of rifled ordnance had called for increased protection, and this was found first by solid constructions of granite, and latterly by massive iron fronts. Examples of these remain in Garrison Fort, Sheerness, and in Hurst Castle at the west end of the Solent. The range of guns being then relatively short, it was necessary to place forts at fairly close intervals, and where the channels to be defended could not be spanned from the shore, massive structures with two or even three tiers of guns, placed as close as on board ship and behind heavy armour, were built up from the ocean bed. On both sides the calibre and weight of guns were increasing, till the enormous sizes of 80 and 100 tons were used both ashore and afloat.

The bombardment of Alexandria established two new principles, or new applications of old principles, by showing the value of concealment and dispersion in reducing the effect of the fire of the fleet. On the old system, two ships firing at one another or ships firing at an iron-fronted fort shot “mainly into the brown”; if they missed the gun aimed at, one to the right or left was likely to be hit; if they missed the water-line, the upper works were in danger. At Alexandria, however, the Egyptian guns were scattered over a long line of shore, and it was soon found that with the guns and gunners available, hits could only be obtained by running in to short range and dealing with one gun at a time.

This new principle was not at once recognized, for systems die hard, and much money and brains were invested in the then existing system. But a modern school was gradually formed; a small group of engineer officers under the headship of Sir Andrew Clarke, the then inspector-general of fortifications, took the matter up, and by degrees the new views prevailed and the modern school of coast defence came into being between 1881 and 1885. Meanwhile important changes had been developing in the gun, the all-important weapon of coast defence, changes due mainly to the gradual supersession of the muzzle-loader by the breech-loader. The latter gave the advantages of quicker loading and more protection for the gun detachment over and above the technical improvements in the gun itself, which gave higher muzzle velocity, greater striking effect and longer effective range.

All this reacted on the general scheme of coast defence by enabling the number of guns to be reduced and the distance between forts increased. On the other hand, the ships, too, gained increased range and increased accuracy of fire, so that it became necessary in many cases to advance the general line of the coast defences farther from the harbour or dockyard to be defended, in order to keep the attackers out of range of the objective.

Another change resulted from an improvement in the method of mounting. Even in the older days discussion had arisen freely on the relative merits of barbette and casemate mounting. In the former the gun fires over a parapet, giving a larger field of view to the gun-layer, and a larger field of fire for the gun, with, however, more exposure for the detachment. The latter gives a restricted view and greater safety to the layer, but unless the casemate takes the form of a revolving turret, the arc of fire is very limited.

An important advantage of the barbette system is its cheapness, and thus in order to obtain with it concealment, suggestions were made for various forms of mounting which would allow of the gun, under the shock of recoil, disappearing behind the parapet to emerge only when loaded and ready for the next round. A mounting of this description for muzzle-loading guns, designed by Colonel Moncrieff, was actually in use in the defences of Alexandria and in H.M.S. “Téméraire.”

But with the increased charges and length of breech-loading guns, a further change was desirable, and after some trials a system of disappearing mountings (see Ordnance: Garrison Mountings) was adopted into the British service.

A word must be now said on the size of gun finally adopted. At first muzzle-loaders figured largely in the British defences, even though these were planned on modern ideas; and even in 1906 muzzle-loading guns still existed and were counted as part of the defences. The sizes of these guns varied from the 32- or 64-pounder, of which the nomenclature depends on the weight of the shell, to the 7-in., 9-in., 10-in., 11-in., 12.5- and finally 17.25-in., the size indicating the calibre. Such a multiplication of sizes was due to gradual improvements in the science of gun manufacture, each advance being hailed as the last word to be said on the subject, and each in turn being rapidly made obsolete by something bigger and better. But with the improvements in gun design which followed the introduction of breech-loaders, the types used in coast defence were gradually narrowed down to two, the 9.2-in. and the 6-in. guns. Of these, the 9.2-in. was considered powerful enough to attack armour at any practical range, while the 6-in. gun was introduced to deal with lightly armed vessels at shorter ranges where 9.2-in. guns were unnecessarily powerful.

A few larger guns of 10-in. calibre have actually been used, but though the British navy has now sealed a 12-in. 50-ton gun as the stock size for battleships, for the heavy armament of the coast defences the War Office remain faithful to the 9.2-in. calibre, preferring to develop improvements rather in the direction of more rapid fire and higher muzzle velocity.

The 6-in. has also been retained and is extensively used for the smaller ports, where attack by powerful vessels is for various reasons considered improbable.

The design of the forts to contain the guns necessarily varied with the type of defence adopted, and the duties which the forts had to fulfil. These duties may be said to be twofold, first to facilitate the service of the guns, and secondly to protect the guns and their detachments from damage by fire from ships, or by close attack from landing parties. The service of the gun is provided for by a system of cartridge and shell magazines (see Ammunition), well protected from fire and suitably arranged. The shelters for the gun detachments must be bomb-proof and fitted with some arrangements for comfort and sanitation. Formerly it was the custom to provide living accommodation for the full garrison in casemates inside each fort, but it is now considered better to provide barrack accommodation in the vicinity and to occupy forts in peace only by a few caretakers. The shelters in the fort itself can thus be kept at the minimum required when actually manning the guns. The protection of the guns and magazines against bombardment is provided, in the British service, mainly by an earthen parapet over a substantial roof or wall of concrete, but immediately round the gun an “apron” of concrete is necessary to withstand the shock of discharge or “blast.”

It has been already mentioned that in the old designs a large number of guns was put in each fort, but with dispersion and improved gun power this number was much reduced. At first the type of fort adopted was for four guns, of which the two in the centre were heavy and the two on the flank of medium power. Such a design was good from the point of view of the engineer; it gave an economical grouping of magazines and shelters and was easily adapted to varying sites, and the smaller guns helped the larger by covering their flanks both towards the sea and also over the land approaches. But from the point of view of the artillery officer the arrangement was faulty, for when the guns are too much separated, ranging has to be carried out separately for each gun. On the other hand, two guns of the same calibre placed near one another can be fought simultaneously and form what is known as a “group.” In the typical 4-gun battery described above, the flank guns had to be fought independently, which was wasteful of officers and staff. Further, in a battery of more than two guns the arc of fire of the centre guns is much restricted by that of the guns on either flank.

For these reasons it is now generally recognized that new works should be designed for only two guns of the same calibre, though 3- or 4-gun batteries are occasionally used in special circumstances.

Protection of the gun detachments against infantry attack is best provided by a line of infantry posts outside and on the flanks of the gun batteries, but as small parties may evade the outposts, or the latter may be driven in, it is necessary to place round each fort a line of obstacles sufficient to protect the guns against a rush and to cover the infantry while it rallies. This obstacle was formerly a wet or dry ditch, with escarp, counterscarp and flanking galleries; but with the new design of parapet a simpler form of obstacle was adopted. This was obtained by carrying down and forward the slope of the parapet to a point well below the level of the surrounding ground, and then placing a stout fence at the foot of the parapet and concealed from view. It is in fact the old principle of the sunk fence, and has this further advantage, that the fence, being visible from the parapet, can be kept under fire by men posted between the guns without any special flanking galleries.

Occasionally two or more batteries are placed inside one line of obstacles, but usually each 2-gun battery is complete in itself.

Cases arise, e.g. with sites on the top of a cliff, where no obstacle is required; in such places the parapet merges into the surrounding ground.

In old days the parapet was shaped with well-defined edges and slopes. Now the parapet slopes gently down to the front and is rounded at the sides, so as to present no definite edge or angle to the enemy, and concealment is furthered by allowing grass or small scrub to grow over the parapet and round the guns. In order to obtain complete concealment from view the background behind the guns must be carefully studied from the point of view of the attack. Sites on the sky-line, and marked contrasts of colour or shape, should be avoided. In some cases extensive planting, amounting to landscape gardening, is justified. This is most easily arranged in the tropics, where plant growth is rapid. In all cases the guns and their mountings should be coloured to blend with the background and thus avoid hard lines and shadows.

Any change of principle such as that of 1885 involves improvements both in guns and their adjuncts. Of these latter the most important was the position-finder designed by Colonel Watkin. This instrument in its simplest form, when the observer is following a ship through the telescope of the instrument, draws on a chart the track of the ship, so that the exact bearing and distance of the latter can be ascertained at any time and communicated to the guns by electrical and other dials, &c. The position-finder may be some distance from the guns it serves, and connected with them by electric cable. The guns can then be placed well under cover and in many cases out of sight of the target, giving a measure of protection which cannot be obtained with any system of direct laying over sights. This instrument has been applied on a high site to control guns placed low, or where guns are so placed as to be liable to obscuration by fog or mist the position-finder can be placed below the fog-line. In either case direct laying is provided for as an alternative. In some defences batteries equipped with old pattern 9-in. muzzle-loading guns, mounted as howitzers for long-range firing, have been placed in folds in the ground so as to be quite invisible from the sea and therefore invulnerable. Such batteries are fought entirely by the position-finder.

The next adjunct to coast defences is the submarine mine. In Great Britain the first submarine mining company dates from 1873, and from that date mining defences were gradually installed both at home and abroad; but the modern system of mining, which for twenty years was maintained at British ports, really started into full life under the impetus of Sir A. Clarke, about the same year (1885) in which we have dated the commencement of the modern coast defence system.

With the increased speed of warships, a method of attack on fortifications was evolved by running past the main defences and either taking them in reverse, or disregarding them and attacking the dockyard or other objective at short range. This was made more possible at most defended ports by the pushing forward of the defences which has been already alluded to, and it is especially dangerous where dockyards or towns are situated some way up a river or estuary, so that once the defences are passed there is a large stretch of water (e.g. the Thames, the Solent, and Cork harbour) in which the enemy can manoeuvre. In such cases there are two possible forms of defence, first by arranging for gun-fire behind the main gun position, usually called the defence of inner waters, and secondly by placing in the entrance and under the fire of the main gun defence some form of obstruction to detain ships under fire. This obstruction can be passive (booms, chains, rows of piles or sunken ships) or active (mines or torpedoes). Passive obstructions are only effective against comparatively small craft, and at important ports mines are the only efficient obstruction which can be used against large vessels.

After some years of experiment, English engineers adopted two main classes of mines, called “observation” and “contact” mines (see Submarine Mines). Both were fired by electricity, which was applied only at the moment a hostile ship was within the dangerous zone of a mine. In the observation mines the moment of applying the electric current was ascertained by a position-finder, which, tracing a ship’s course on a chart, made an electrical connexion at the moment the ship was over a mine. These mines were placed so as to be well below the bottom of any ships afloat and were used in channels which it was desired to leave open for the entrance of friendly vessels. Contact mines, which are moored a few feet below the surface of the water, are fired after certain electrical connexions have been made in a firing room on shore by the ship itself striking against the mine. These are used in waters which it is intended to deny to friend and foe. Except in narrow waters where the whole width of the channel was required for friendly traffic, contact mines were generally used to limit the width of the channel to the minimum consistent with the amount of friendly traffic which would use the port in war. It will be readily understood that by bending this channel and disclosing its exact position only to special pilots, a very complete measure of security against surprise would be obtained. In English ports the practical importance of allowing free ingress for friendly traffic overruled all other considerations, and the friendly channels were always straight and coincided with some part of the usual fairway channel. They were also carefully marked by lightships and buoys.

A variation of the submarine mine is the Brennan torpedo, purchased by the British government about 1890. This differs from the torpedo used on board ship, mainly by the fact that the engine-power which drives it is on shore and connected with the torpedo by two strong wires. These wires are wound out of the torpedo by the engine, and by varying the strain on the two wires very accurate control of the steering can be obtained. This torpedo shares with the submarine mine the disadvantages that it must wait for the enemy to venture within its range, and with all other forms of defence (except contact mines), that it is made useless by fog or rain. As compared with a mine it has the advantage of being unaffected by tide or depth, and of forming no obstruction to traffic, except when actually in action. It was installed at the principal ports only.

The system of defence hitherto described is thus a main gun defence of 9.2-in. and 6-in. guns pushed well forward, assisted by position-finders, mine-fields and torpedo stations, and with some gun defence of inner waters. Subject to improvements in patterns of guns and mountings—of which the most important has been the substitution of barbette mounting and shield for the recoil mounting described above—this system held the field up to 1905, when, partly as a result of the experience of the Russo-Japanese War, and partly owing to the alteration of the naval balance of power due to the destruction of the Russian fleet, both the scale and system of defence were very considerably modified.

We can now consider another branch of defence, which was evolved pari passu with the automobile torpedo, and was therefore almost non-existent in 1885. In this year the boats specially built for carrying torpedoes were little more than launches, but in the next five years was developed the type of first-class torpedo boat. This, while seaworthy, was limited as to its radius of action by the small amount of coal it would carry. But with a possibly hostile coast only a few hours’ steam away, and with foreign harbours thronged with torpedo craft, it became necessary for the British government especially to consider this form of attack and its antidote. It was obvious that in daytime and in clear weather such an attack would have little chance of success, also that in no circumstances would torpedo boats be able to damage fixed defences. Their best chance was attack by night, and the only form of attack was that referred to above as “running past,” that is, an attempt to evade the defences and to attack ships or docks inside. The light draught of torpedo boats and their comparative invisibility favoured this form of attack.

To meet it the first requirement was some form of illumination of the defended channel. Experiments in the attack and defence of defended harbours took place at Gosport in 1879 and 1880, at Milford Haven in 1885, at Berehaven (by the royal navy) in 1886, at Langston Harbour in 1887, and a series at the Needles entrance of the Isle of Wight up to 1892. During the course of these experiments various methods of illumination were tried, but by far the best was found to be the light from an electric arc-lamp of high power projected by powerful reflectors. At first these were used as concentrated beams forming a pencil of light with an angular opening of about 2° to 3°. Such a beam directed at an incoming ship gives effective illumination up to a mile or more from the source of light, but has the disadvantage that it must be moved so as to follow the ship’s movements. Each beam thus lights only one ship at a time, and the movements of several beams crossing and recrossing have a very confusing effect, with the consequent risk that a proportion of the attacking vessels may slip through unnoticed.

An alternative method of using electric lights is to arrange the projector so that the light comes out in a fan (generally of 30° divergence). Two or three such lights are usually placed side by side, forming an illuminated fan of considerable divergence. These fans are now used for the main defence, with in front of them one or more search-lights to warn the defences of the approach of ships. There is some loss of range when using these fans as compared with search-lights, but by occupying both sides of a channel and placing the defences against torpedo boats at the narrowest point, an effective illumination can be obtained in moderate weather.

Heavy guns can, of course, be fired against torpedo boats, but their rate of fire is relatively slow, and at first they had also the disadvantage of using black powder, the smoke of which obscured the lights.

A small quick-firing gun using smokeless powder was seen to be a necessity. At first the 6-pounder was adopted as the stock size supplemented by machine guns for close range, but soon afterwards it became necessary to reconsider the scale of anti-torpedo boat defences, owing first to the increased size of first-class torpedo boats, and secondly to the introduction of a new type of vessel, the torpedo boat destroyer. The increased size of torpedo boats, and improved arrangements for the distribution of coal on board, made these boats practically proof against 6-pounder guns and necessitated the introduction of the 12-pounder. The torpedo boat destroyer, originally introduced to chase and destroy torpedo boats, not only justified its existence by checking the construction of more torpedo boats, but in addition became itself a sea-going torpedo craft, and thus increased the menace to defended ports and also the area over which this form of attack would be dangerous.

This development was met by an increased number of 12-pounder guns, assisted in the more important places by 4.7-in. (and latterly 4-in.) guns, and also by an increased number of lights, both guns and lights increasing at some places nearly fourfold. But even with the best possible arrangement of this form of defence, the possibility of interference by fog, mist or rain introduces a considerable element of uncertainty.

About the same time, and largely on account of the demand for better and quicker firing, the “automatic sight” was introduced (see Ordnance: Garrison; and Sights). In this, a development of the principle of the position-finder, the act of bringing an object into the field of the auto-sight automatically lays the gun. In order to take full advantage of this, the ammunition was made up into a cartridge with powder and shell in one case to allow of the quickest possible loading. It may be added that the efficiency of the auto-sight depends on the gun being a certain height above the water, and that therefore the rise and fall of tide has to be allowed for in setting the sight.

In view of the possible interference by fog it was thought wise at an early stage to provide, towards the rear of the defences, some form of physical obstacle behind which ships could lie in safety. Such an obstacle had been designed in the early days by the Royal Engineers and took the form of a “boom” of baulks of timber secured by chains. Such booms were limited in size by considerations of expense and were only partially successful. About 1892 the British navy took the matter up and began experiments on a larger scale, substituting wire hawsers for chains and using old gunboats to divide the booms up into sections of convenient length. The result was that booms were definitely adopted as an adjunct of coast defence. Their place is behind the lighted area, but within reach of some of the anti-torpedo boat batteries.

Other forms of obstacle to torpedo boat attack, based on a modification of contact mines or a combination of mines and passive obstructions, have been tried but never definitely adopted, though some form of under-water defence of this description seems necessary to meet attack by submarines.

We may now summarize the anti-torpedo boat defences. These are, first, an outpost or look-out line of electric search-lights, then a main lighted area composed of fixed lights with which there are a considerable number of 12-pounder or 4-in. Q.F. guns fitted with auto-sights, and behind all this, usually at the narrowest part of the entrance, the boom.

Once coast defences are designed and installed, little change is possible during an attack, so that the operation of fighting a system of defence, such as we have considered above, is mainly a matter of peace training of gun-crews, electric light men and look-outs, coupled with careful organization. To facilitate the transmission of order and intelligence, a considerable system of telephonic and other electrical communication has been established. This may be considered under the three heads of (1) orders, (2) intelligence, (3) administration.

The communication of orders follows the organization adopted for the whole fortress. Each fortress is commanded by a fortress commander, who has a suitable staff. This officer sends orders to commanders of artillery, engineers, and infantry. The artillery officer in charge of a group of batteries is called a “fire commander”; his command is generally confined to such batteries as fire over the same area of water and can mutually support one another. Thus there may be several fire commanders at a defended port. Anti-torpedo boat batteries are not in a fire command, and are connected to the telephone system for intelligence only and not for orders. The engineers require orders for the control of electric lights or Brennan torpedo. The officer in charge of a group of lights or of a torpedo station is called a director. Though receiving orders direct from the fortress commander, he has also to co-operate with the nearest artillery commander. The infantry are posted on the flanks of the fixed defences, or on the land front. They are divided into suitable groups, each under a commanding officer, who communicates with the fortress commander. In large fortresses the area is divided into sections, each including some portion of the artillery, engineers, and infantry defence. In such cases the section commanders receive orders from the fortress commander and pass them on to their subordinates.

The intelligence system includes communication with the naval signal stations in the vicinity, one of which is specially selected for each port as the warning station and is directly connected to some part of the defences. Another part of the intelligence system deals with the arrangements for examining all ships entering a harbour. This is usually effected by posting in each entrance examination vessels, which are in communication by signal with a battery or selected post on shore. Any points on shore which can see the approaches are connected by a special alarm circuit, mainly for use in case of torpedo boat attack.

The administrative system of telephones is used for daily routine messages. These usually take the form of telephone lines radiating from a central exchange. In many stations the same lines may be used for command and administration, or intelligence and command, but at the larger stations each class of line is kept distinct.  (W. B. B.)