Coast Defence: Description and Purpose


Coast Defence
Coast Batteries differ from works that are designed to resist land based attacks in several ways. They rarely were required to withstand a siege or to resist accurate fire such as that delivered from siege batteries, but they could be subjected to fire from the heaviest projectiles available to an enemy. Attacks on a coast battery could be sudden and with the full force that an enemy could muster giving little time for preparation of the defence. If the purpose of an enemy was to run past them in order to attack a primary target the coast defence battery would have little time to produce an effective attack. Coast batteries therefore did not necessarily need a great amount of casemate accommodation for men or for stores but they did require heavy guns, good and safe ammunition storage and efficient methods to supply the guns with ammunition. In the larger coast batteries, which also served as accommodation for a sizeable portion of men deployed at other coast defences nearby, military stores and workshops would be provided. In the smaller batteries there would need to be shelters for the men to withstand direct bombardment and some protection from assault by a small landing party.


Plate from Lewis: Permanent Fortification for English Engineers: 1890

Mathew Coomber, who is investigating and researching the defences of Mauritius, has identified this battery as Tombeau Battery in Mauritius. It is also known as Albert Battery in Mauritius. (Thanks to John P. Cartwright for pointing this out) Col.Lewis R.E. writes in 1898: The guns are old ones, two 10-inch RML and two 64pr RML. The ground it stands on is only nine feet above the sea level, but the use of barbette mountings at such a small height is justified by the fact that a reef of the coast prevents ships coming within machine gun range. The slope of the parapet is prolonged below the ground level, as in the cae of Twydale redoubt, the ditch containing and iron fence, and being protected by fire from the parapet. The guns are 200ft apart. The ammunition stores are in the centre as before, and the immediate service to the guns is by means of recesses, the charges being carried round by the rear of the emplacements. In a similar case the centre guns might be served directly from the stores by means of lifts or of ramps which can be used if not steeper than 1 in 7. The defence of the gorge is concentrated at one angle in order to economise men.



The main purposes of coast defence was to:
1. Close the passage of a river or channel.
2. Protect a town or dockyard from bombardment.
3. Deny the use of an anchorage.
4. Defend a landing place.
5. Protect and close the flank of a land work.


Coast defence guns may be required to fulfil the following duties:
1. Attack armour.
2. Attack un-armoured and protected parts of a ship (General Attack).
3. Attack decks by plunging fire or high angle fire.
4. Attack men using shrapnel, machine or field gun.
5. Attack boats and small vessels using light pieces.
For 1 & 2: heavy R.M.L. guns and later B.L. guns were used.
For 4 & 5: machine guns and Quick Fire guns were employed.
For 3: the mortar and later high angle mountings were needed. Mortars were quickly declared obsolete for this purpose.
For 1: a variety of defence methods were employed including all of the above supplemented by the use of submarine mines and Brennan guided torpedoes.


Plate from Lewis: Permanent Fortification for English Engineers: 1890

This is the battery designed for Frenchman's Point at Tynemouth. Col Lewis R.E. desribes it thus:
Having a cliff in front, partly quarried, partly natural, no front ditch of other defence is required. The parapet is of the sloping type and dies out on the ground. The armament is two 9.2inch B.L. and two 6- inch B.L. all on HP mountings. The guns are placed 200ft apart and are 88ft above the sea. From it's position in an indentation in the general line of the coast, the battery cannot be enfiladed from the sea or taken in the rear. Any shot missing them will pass by and do no harm. The battery has but small relief above the ground and the changes of height are slight and the slopes flat, so that it may be expected to harmonise well with the surrounding flat country. It is proposed to plant shrubs along the gorge parapet so as to break up the outline. The ammunition service is from a central magazine for shell and cartridges, to recesses near the guns, from which the charges are taken for use. Casemate accommodation is provided for the garrison perhaps rather in excess of the requirements, for a naval attack cannot last for long and there is no need for the men to live under cover. The interior of the battey is sunk so that the communications will be very safe. The gorge is defended by a parapet of the Twydale type.


For the purpose of achieving the above defence each battery consisted of emplacements for guns of dimensions suited to the gun employed. Each emplacement needed enough room for working the gun conveniently. Magazine accommodation was needed to supply the guns efficiently and quickly in time of attack. Main magazines could be used during peace time whilst expense magazines served this purpose during time of war. The gun detachments required accommodation, which in peace time would be a larger defence work with ample barrack space. In time of war shelters would be proved in the smaller defence works that did not have permanent barrack accommodation. The guns were grouped according to their nature or intended field of fire in groups of one to five guns under one officer, or N.C.O. Each gun or group of guns required a fighting position for the officer directing it in action. Position Finders were needed to enable an observer to determine and communicate to the gun the exact range and bearing of a target. The two types of position finder in use were the depression (D.R.F.) and the horizontal range finder (P.F.) The D.R.F. needed sufficient height to determine range.


The type of Coast Defence batteries in use were:
1. Open batteries in which there would be three classes of mountings: barbette, disappearing and high angle.
2. Open batteries with shields.
3. Open batteries with shields and permanent overhead cover.
4. Casemated batteries of masonry with iron shields.
5. Continuous iron-fronted casemates.
6. Curve-fronted casemates.


Guns and Mountings.
The armament in a fortress or coast defence battery could be classed as primary and secondary.
The primary armament consisted of R.M.L. guns from 7-inch calibre upwards, later B.L. guns from 6-inch upwards and Q.F. guns.
The secondary armament consisted of smaller pieces for flank and rearwards defence and could include guns on travelling mountings for defence of landing places and mine fields.


Barbette Mountings
Old forms of barbette emplacements were used for the 64pr R.M.L. and 7-inch R.B.L. guns where the parapet was low. Later emplacements for the 7-inch R.M.L. to 12.5-inch R.M.L. guns used dwarf platforms to fire over a parapet of up to 4ft 3inches in height. Blocked-up mountings allowed guns from the 64pr R.M.L. to the 12.5-inch R.M.L. to fire over higher parapets of six feet in height. Emplacements for the 10-inch and 11-inch R.M.L.s were provided with a step or fixed loading stage to facilitate their loading. An improved form of this with ‘sunken loading way’ around the drum on which the gun sat was developed to protect the gun crew from direct fire.


Plate from Lewis: Permanent Fortification for English Engineers: 1890


Disappearing Mountings
The two types of mounting developed were the counterweight system and the Hydro-Pneumatic (H.P.) system. The former ‘Moncrieff’ mounting was mainly employed on land front forts using the 7-inch R.M.L. 7-inch R.B.L. and 64pr R.M.L. guns but one example of the 9-inch R.M.L. was deployed at Newhaven Fort. The H.P. mounting was used for the 8-inch (not in the U.K.) 9-inch, 9.2-inch and 10-inch B.L. guns. All of these mountings were in pits with concrete walls. The H.P. mountings also had overhead cover in the form of turtle shields. One example of a 13.5inch B.L. gun was mounted on an H.P. Mounting at Penlee Battery, Plymouth.


Plate from Lewis: Permanent Fortification for English Engineers: 1890


High Angle Mountings
The 9-inch and 10-inch R.M.L. guns were adapted to be fired off special mountings that allowed elevations from 20 to 70 degrees. Some high angle batteries were constructed to take this class of mounting and were positioned such that they could bring plunging fire to bear on the decks of armoured ships whilst the battery itself was obscured from direct view and therefore protected. These batteries were short lived as better B.L. mountings made them redundant.


Fort Cumberland High Angle Battery


Casemate Mountings
Guns in casemates were mounted on traversing slides (platforms) worked on A pivot racers (where the imaginary pivot was in front of the gun). The recoil was checked using compression plates or hydraulic buffers. These mountings were for 7-inch R.M.L. guns and upwards. The heaviest employed was the 12.5-inch R.M.L. although special yoke mountings were adopted for the Spithead Forts for large B.L. guns. In some casemates Q.F. saddle mountings could be employed.


Plate from Lewis: Permanent Fortification for English Engineers: 1890


Requirements of Coast Defence Batteries
The site for a coast defence battery was selected by the necessity for defending precise areas of water. There were three things to be considered:
1. The availability of suitable foundations that could support the heavy mass of concrete for the emplacements and the guns they were to hold.
2. The height above sea level to provide superiority of fire over any enemy vessel.
3. The facilities for directing the fire of the battery using position finders, range finders or by direct laying.


By the 1890s casemated batteries were rarely considered and open batteries with gun pits that were open to the rear were preferred. The emplacements of concrete were to allow each gun the greatest arc of fire obtainable. Side walls were to be as short as possible so as not to trap shells which had passed over the gun. Shelters and magazine stores could be placed beneath the parapet or in traverses between the guns. Close to the gun cartridge recesses were needed for use in emergency. Shells could be placed in similar recesses or stood round the front of the emplacement. On one side of the gun was a recess to take the firing plug. Here the gun captain stood ready to insert the plug before the gun could be fired electrically. Another recess was for the range dials which showed the amount of training and elevation to be given to the gun when its fire was directed by the position finder. This recess also held the battery. Ring bolts set into the wall of the emplacement were used to assist with mounting the equipment. Ammunition lifts were placed to open near, but not into, the emplacement. The fire commander needed a fighting station with shelter and room for his charts. This could be inside the battery at a P.F. station or outside near a D.R.F. He needed full power of directing the fire of his guns and observing its effect by being able to see the water covered by his guns. He was to be in electrical communication with his section commander. Barrack accommodation was not necessary as engagements would be short but some shelter might be provided for crew not engaged in action or for troops that might on mobilisation be permanently employed in the battery. A guard house was need in peace time to give accommodation to men in charge. Large main magazines were seldom required but expense magazines would allow 200 rounds per gun to be stored in the battery. Shells for the larger guns of 7-inch upwards were stored on end in the expense shell stores whilst smaller shells were piled. Cartridges for heavy guns were stored in zinc cylinders which were piled not more than three in height. For smaller guns metal lined cases were used to store the cartridges. Cartridge stores needed shifting lobbies whilst shells stores did not. All shell stores were provided with a shelf on which to store fuzes and tubes. Shells were sent up to the guns from the magazines using a lift or on a trolley. Cartridges were delivered by lifts under cover wherever possible. Each battery required an artillery store for reserve and unserviceable stores. Side arms for operating the guns were stored on racks in the artillery store or in a side arm and tackle store. A laboratory might be required in some batteries to serve either as a shell or cartridge filling room, but never both at the same time. A smith’s shop might also be required so that repairs could be undertaken. At least two sites for range finders were needed, one on each flank of each fire command. Where movable armament was provided storage room was needed.