SEA ATTACK To repel this, naval action alone must be ruled out. A fleet can not have its freedom for offence crippled by being tied to the mouths of harbours. Similarly air force action alone must be ruled out, partly for the same reason as a fleet and partly because aircraft carrying bombs or torpedoes are not accurate enough for reliance to be placed on them alone to defeat a naval enemy. Therefore the onus of the defence must fall on the land forces although the other two must co-operate. The division of responsi bility will be somewhat as follows : (i) The army provides all artillery and other defences actually on the land against all forms of attack.
(ii) The navy provides for distant observation and defence on the sea beyond the power of the land forces, and for sea ob structions such as mines or nets.
(iii) The air force, if available, provides distant air observation and co-operates with the other services in attacking enemy sea and aircraft and in assisting the fire of long range guns.
The defences required on land will vary according to the nature of the sea attack.
Defences Against Deliberate Bombardment, Probably from Heavy Ships.—To guard against this, heavy artillery must be mounted. As the ranges of naval guns have lengthened up to as much as 40,000 yards, and ships are well protected, powerful guns are required on shore, say from i 2in. calibre upwards. In the case of ports where, owing to shallow water or for geograph ical or other reasons it is considered that bombardment need be expected from more lightly armed ships only, lighter guns will suffice.
The guns must be placed so that all the water whence hostile fire is possible may be covered. In some places ships can fire across intervening land. Wherever possible guns should be pushed forward from the object of defence (harbour, dockyard, etc.) . The aim should be to keep ships beyond bombarding range of the object or at least to bring effective fire on the ships before the latter come within that range. If the object of defence is close to the sea, owing to the coastline being unindented, the number of guns will have to be increased.
The guns will be dispersed in batteries but should be able to assist each other with their fire. Generally, two guns will be in each battery, but sometimes they may be placed singly. A gun must have a firm support in the form of a heavy pedestal on a concrete foundation, and the usual mounting is the open or bar bette type, the only protection for the crew of the gun being a shield which is part of the mounting. Parapets are not required round the gun as the angle of descent of hostile shell would be too steep to make them of service. It is probable that heavy guns will be placed behind features of the ground so that they will be unseen from the sea. In any case they will have to have their fire directed by some instruments separate from them, so that they lose nothing in this way, while there would be the advantage of easier communications up to them and probably greater latitude in choice of sites.
Guns mounted on a railway are not suitable for coast defence as they cannot change their direction of fire sufficiently rapidly. A gun and mounting which can travel by rail and be lowered on to a fixed pivot in a short time, was used by the Germans on the Belgian coast during the World War. Some of this type have been adopted by the United States of America. But the sole ad vantage in these mountings, that of being able to reinforce threat ened points, is more than counterbalanced by not having the guns always on the spot where their crews can be trained with them. This is especially the case where the men come from local sources.
In order to be "knocked out" by a ship a coast gun must receive a direct hit. The chances of this are very slight, since the target presented to the ship is so small. Owing to this and to the very powerful action of a heavy shell, if it does hit, it is better to obtain protection for the battery by dispersing its various parts, giving them only slight material cover than to concentrate them in one place and protect them by sheer mass of material. Concentration would be necessitated on account of the cost of such protection. By this dispersion each part of the battery becomes a separate target for a ship, the guns being separated by some 25o to Soo yards, and the ammunition stored in isolated buildings. These should be above ground, the structure being proof against splin ters only. Advantage should be taken however of the shelter given by any features of the ground. Each gun should have sev eral cartridge and shell stores, their internal details being so designed as to allow the ammunition to be handled as quickly as possible. The moving of the shells requires special attention as they are heavy, while the cartridges must be kept at the cor rect temperature. The stores should not be close to the guns and should have good intervals between themselves, while the means of communication between the battery and the nucleus of the defence, whether it be railway, tramway or road, should pass close beside them. The ,ammunition should be supplied to the guns on small trucks running on light tramways or on concrete paths.
Accessory parts of a heavy gun battery will be some form of power for working the guns (probably electric), stores for artil lery material, etc., and the structures for housing the officers in charge of the guns and their staff, together with the ends of the electrical cables which enable them to receive orders from their superiors and information from the observation posts which give the data for aiming the gun aright.
Range-finding and Observation of Battery Fire.—This is carried out as far as possible by instruments in the above posts, which are established in places whence a view is obtained over the waters commanded by the guns. The principal instru ment used is termed the horizontal-base position-finder. This requires a structure at each end of the base to house the angle finding instruments and their gear. The posts are generally some thousands of yards apart and should be at as great a height as possible in order to obtain the necessary range of view. On low lying sites use may be made of existing high buildings or it may be necessary to erect towers for the purpose. The posts should be as inconspicuous as possible, though this is difficult to arrange in the case of a tower.
The system of determining the position of an enemy ship is that one post sends its information to the other, called the re ceiver, where the two observations are combined, either by auto matic means or by plotting them graphically. The former method requires more gear and less men than the latter ; the difference in speed is slight. The final result, as sent to the battery, gives the range and bearing of the target ship from the gun. The battery commander should be in a structure beside the receiving post, the position selected being fairly near the battery but well to one flank.
Instruments for important guns are often duplicated or alter natives are used such as the self-contained Barr and Stroud range finder, which has the necessary base within the instrument itself.
At ranges beyond the view of land instruments or in cases where the ships use extensive smoke clouds for concealment, the assistance of aircraft will have to be obtained to observe the fire of the guns. This will necessitate the provision of a wireless sta tion for the battery commander. It should be realized that aerial observation will not be so accurate as that from fixed instruments.
It is worth noting here that the possibility of jamming the wireless of aircraft has not yet•been fully tested. If feasible their value for observation purposes would largely disappear.
A battery to deliver indirect fire as described above is unseen from the sea, but it has to reckon with hostile observers in the air "spotting" the fire of the ships. These observers may some times be impeded by the defending aircraft and anti-aircraft artillery but other measures can be taken. It is possible to sur round the battery area with a screen of dense smoke. Also the general lay-out of the battery should be made as indefinite as possible, long straight lines should never be used for any part of it. The object of this is to make it difficult for the enemy's airmen to estimate the position of the fall of shell. To further this end, in suitable localities the whole battery area might be planted with trees at intervals. For the same reason portions of a battery, such as tramways, paths, etc., may be concealed under what is known as camouflage (q.v.). This would be done on the outbreak of war only, as it is impossible to prevent any potential enemy from gain ing information about such a work • as a coast battery erected in peace.
Defences Against Attack by Cruisers.—A deliberate bom bardment from heavy ships is not an operation to be undertaken lightly by an enemy, owing to the great danger to which these important vessels are exposed and the large expenditure of ammu nition involved. A more easily conducted bombardment would be a short one, or what may be called a raid. This may be car ried out from heavy ships but is more likely to be the work of cruisers. At defended ports, where it has been decided that only cruiser attack is probable, the guns can be of a lighter nature. Also, since the ranges at which such actions will be fought will be shorter than in the case of heavy ships and may get very short, the guns should be placed where they can see the water them selves (direct-fire batteries). These medium batteries will be sit uated, as regards the object of defence, on much the same lines as the heavy batteries, but some of their fire should be able to com mand the water up to the entrance of the harbour and the guns should be at a good height above the water. The battery designs would follow the same general idea as the heavy batteries, modi fied by the fact that the battery site may be exposed to view from the sea. Everything possible must be done to make the various parts inconspicuous. The guns, probably two to a battery, should be closer together than the heavy guns, firing from mountings of a similar type (with modifications) with no parapet in front. To render them inconspicuous the guns must have a background as viewed from the sea which may have to be artificial and paint, judiciously applied to the guns and visible concrete, will assist greatly.
The ammunition stores should be small and dispersed and they must not form objects conspicuous from the sea, every advantage being taken of features of the ground to hide them. Other parts of these batteries would not differ materially from those of the heavy batteries. In both forms of batteries already described ac commodation for the officers and men would be restricted to war shelters in the battery area but dispersed irregularly.
Defences Against Attack at Close Quarters.—This attack may be made with the endeavour to penetrate the channel and to torpedo ships lying inside, or to attack dockgates. The craft em ployed will probably be of a much smaller nature, possibly destroyers or fast motor boats, while submarines might be used, but in most cases they would not be able to enter submerged. The attackers will generally move at high speed.
To meet this form of attack light guns with a rapid rate of fire are required to cover the channel entrance and the water close in front of it. These batteries would be designed so as to give the fullest effect to the guns, the question of protection not being of great importance as the hostile craft will not be able to delay in order to engage them. In these light batteries the ammu nition should be kept close to the guns, and shelters for the men on duty should be provided in the immediate vicinity, with sleep ing accommodation for the remainder inside the battery. These batteries should not be on very low sites as it is advisable to be able to use the automatic sight, which requires some height. This sight is an adaptation of the vertical-base position-finder in which the act of bringing the target into the field of the sight lays the gun correctly.
Close attacks are most probable at night so that the water in the entrance and near it must be illuminated effectively. This is done by powerful electric searchlights which have a range of some 2,000 yards and upwards, varying with the state of the atmosphere. They may be used as observation lights, illuminated area lights or fighting lights. Observation lights have concentrated beams and are placed at the outer edge of the near defences, being gen erally in pairs. For ranges beyond that of the lights the artillery can assist by firing star-shell. Illuminated area lights have dis persed beams and are used to light an area of water. Fighting lights are concentrated beams specifically allotted to serve par ticular guns or batteries.
Defences Against Attempts to Block Narrow Channels by Sinking Ships in Them.—(See BELGIAN COAST OPERATIONS': Zeebrugge.) Where it is considered that such attacks are pos sible, naval assistance is most desirable for the defence, but guns and lights must be provided also to stop the ships before they reach the narrow channel. For some time after 1890 the Brennan torpedo, controlled mechanically from the shore, was in the British service against such attacks. It is possible that counter-attack by torpedoes, fired from the shore, or carried on manless electrically controlled motor craft, might be used. Such craft, however, might find better employment against ships carry ing out deliberate bombardment.
Defences Against Gas Attack.—Such attack might consist of the use of gas clouds or gas shell. If this is deemed possible special measures will be necessary to make gas-proof such places as observation posts, command posts, etc., since the use of ordi nary anti-gas appliances worn on the person interferes greatly with the use of instruments.