the Gallipot! Peninsula the Germans commenced the construc- tion of an indirect-fire battery inland from Cape Helles, which was not quite finished at the end of the war, while at the Black Sea entrance of the Bosporus on the European side there was a bat- tery constructed by the Germans which was sited (designedly or not) in a peculiarly clever manner. It was near Rumeli Fenner and contained three 24-cm. guns. Owing to the configuration of the ground it was an indirect-fire battery if used against ships in the Black Sea to the west of the Bosporus, while in the event of vessels trying to force the entrance the guns could use direct fire at a comparatively short range.
Size of Guns. There is a certain amount of disagreement as regards the size of guns required in coast batteries. In the case of a straight coast-line the guns must be powerful enough and possess sufficient range to engage and cause the retirement of the ships, or at all events to make them confine their efforts to reply- ing to the batteries. This means that they must be equal in ranging power to the guns of the enemy.
When an approach channel exists, however, and the batteries can be pushed forward, it is not really necessary that the coast guns should be as long-ranging as those of the ships. They only require to have sufficient range to enable them to bring effective fire on the ships before they come within bombarding range of the object of attack. To obtain long range it is also not really essential to have guns of very large calibre, although the life of a large gun is certainly longer than that of a smaller one of equal range. Natur- ally, the shell fired by a coast gun must have a real effect on a ship. But at the range at which actions are now fought the angle of descent is so great that the deck is more often than not the place where a hit would take place, and the protection in this part of a ship is not very great. On the Belgian coast the Germans had five 15-in. guns (38-011.), four 12-in., and a number of ll-in., but it seems questionable whether, provided sufficient range can be economically obtained, a gun of n-in. or possibly 12-in. would not be quite powerful enough for a coast battery against any kind of vessel. As already stated, it is necessary to reduce to a minimum the amount of material and number of men employed in coast defences, and the smaller the gun the greater the economy in both.
It has often been advocated that guns on railway mountings should be used for coast defence, and at first sight they appear to be advantageous. They can be moved comparatively easily from place to place in accordance with strategic requirements. But the ordinary railway heavy-gun mounting is not suited for use against ships since it does not give sufficient traverse, as it can be fired only a few degrees on either side of the axis of the railway. Ships are moving targets and coast guns must have a very large arc of fire. For considerable variations in the line of fire a railway gun has to be on a curve of the line and move along the curve as required. This is too slow for use against a moving target. From the point of view of protection the faculty of being able to be moved is hardly required, especially if the gun is firing indirectly. There may be strategic advantages however in having movable coast guns, design- ing the mountings so that they can be moved on rails and can also be transferred in a fairly short time from their travelling wheels on to prepared pivots.
Range-finding. For the modern coast-defence gun it is essential that the best possible means of range-finding be employed. Many instruments have been used for the purpose. Some are adapted to give only the range of a target from the site of the range-finder, others termed position-finders give the actual position of the target on a chart of suitable scale and therefore its relation to the gun position, which is also marked on the chart.
Both range-finders and position-finders are of different kinds. Some depend on a vertical base and so require correction for tide level. Others depend upon a horizontal base and therefore must be in pairs, one at each end of it. In this case one is known as the transmitting instrument and the other as the receiving, the latter being near the gun. In a different class again is the self-contained range-finder, in which telescopes at either end of a tube from 3 to 33 ft. long, furnished with prisms, conduct the visual rays to cen- tral object-glasses telescopes and object-glasses being so controlled by mechanism that when the two images of the target are in a cer- tain definite agreement the range is marked mechanically.
The long ranges now required practically put out of court all instruments except those depending on a horizontal base, which must be sufficiently long to obtain intersections at the target that are not too acute. There are two classes of this system, one in which the receiving instrument itself combines the observations of the two and the results are automatically recorded on dials at the gun, the other in which the observations of both instruments are combined graphically at a central plotting station and the range and training are telephoned to the battery. The former sys- tem has the advantage of using fewer operators than the latter, but it requires more elaborate instruments and a larger number of electric circuits. The latter system is hardly any slower than the former, and its communications consist of telephones only. It is possibly the one best suited to conditions of active service.
The chambers required for the angle-measuring instruments are quite small, and though they must be in direct view of the sea they can easily be made very inconspicuous. The receiving instrument
should be somewhere near the battery: if an indirect-fire battery it should be nearly straight in front of It. For economy, principally, it is customary for one pair of instruments to suffice for all the guns of a battery, one gun being selected as the " master," and the other guns are laid by previously worked-out corrections (known as group differences) upon the training of the master gun.
In order that the instruments can have sufficient range of vision it is necessary that they should be at a considerable height above sea-level. This is not always easy of attainment on a low-lying coast. In order to see the horizon at 50,000 yd. an observer must be a little more than 450 ft. above sea-level. But for coast-defence purposes a lesser height would serve, as the target ship will have some height above horizon. For instance, the records of a minor engagement between a German n-in. battery near Blankenberghe, Belgium, and one or two British ships, show that the greatest range used by the battery was 27,000 yards. The instrumental system was a long-base position-finding one. The base was 9,445 yd., the receiving instrument was no ft. above sea-level, on the top of an hotel, and the transmitter was on the top of a house on the dunes, the instrument being 90 ft. above sea-level. This latter height has a sea horizon of 22,090 yd., but the battery was 1,670 yd. back from the sea. Thus the transmitter was laid on a target more than a mile beyond its sea horizon.
The Germans made great use of the tall buildings on the Belgian coast for their observing instruments, but it may be necessary to erect towers to obtain the requisite height.
The question of visibility is a very important one in the matter of range-finding, especially in such a climate as that of Great Britain. There are many days on the British coasts when a view of anything like 50,000 yd. is impossible, owing to sea fogs. Such are often low-lying, and it might be possible to overcome them by the use of captive balloons. Another means of correcting fire is the employment of aircraft, which may be used by both sides in the contest. Here length of range is immaterial, but the accuracy of observation is naturally far less than that from instruments.
Self-contained instruments (such as the Barr and Stroud and the Zeiss) have been mentioned above. These are range-finders only. They were supplied in large number to the German bat- teries on the Belgian coast, but the records show that they were not relied on for long ranges, but regarded as stand-bys in the event of anything happening to the long-base system.
Design of Batteries. The experiences of the World War show that the battery of the future can be greatly simplified. No longer need it be regarded as a fort, and the fact can be frankly accepted that the chances of damage by hostile naval fire are extremely few ; the batteries may be designed accordingly. The guns require their stable platforms of concrete, but parapets are not necessary. Ammunition can be stored in light weather-proof structures or in covered railway wagons on a feeding railway, protection being sought by dispersion rather than by thickness of covering. The supply of ammunition to the guns must naturally be made as easy as possible, and great use can be made of light tramways.
This type of battery was used by the Germans in Belgium in the later stages of the war. At first their batteries were all of the type in use before the war, with heavy concrete and earth protec- tion over the magazines. But after their experience of many bom- bardments they practically abandoned all material protection. Also, while the earlier range-finding stations had thick concrete protec- tion the later structures were weather-proof only.
Effect of Aircraft. The war has introduced a new arm which cannot be ignored in any branch of the military art, namely, the air service. As already mentioned, aircraft can and will be used for correcting the fire both of ships and of coast batteries. But it is also necessary to consider the offensive action of aircraft against batteries. Unless the aircraft can descend low enough to make use of machine-gun fire this action will consist of bomb-diop- ping. The use of bombs is very similar to the use of long-range large shell, and, at all events up to the present, it is extremely diffi- cult with bombs to obtain any accuracy against small targets.
A coast-battery gun emplacement may be taken to be about 12 yd. in diameter. If an aeroplane were travelling at a speed of 120 m.p.h., in order to get a direct hit on such a target the bomb must be released at an exact fifth of a second, the plane must be flying exactly across the emplacement, and there must be no wind at all, or at all events no variation in the wind, during the descent of the bomb. All these conditions are very difficult to fulfil conjointly, but practically only direct hits will put the gun out of action. It would also be quite easy to erect vertical splinter-proof protec- tion round an emplacement to guard against approximate hits, although this has the disadvantage of making it more conspicuous to the eye of an aerial observer. Efficient overhead cover for the guns is almost impossible to provide, and is not really required.
It would probably be advisable to furnish some material protec- tion for the gun detachments when not in action, as the explosion of large bombs in close vicinity is a trying experience.
However, the main protection of batteries against aerial attack will lie in the use of counter aircraft and of anti-aircraft guns. Even with the latter only hostile craft will have to keep high up, and the accuracy of their aim will be very 1 greatly impaired. Therefore every battery must be within the rayon of some anti-aircraft guns.
