The principles covering the defense of advanced bases are identical with those governing permanent bases, but, owing to the conditions under which the defending force is operating, they cannot be applied to the same degree. This, however, is counterbalanced by the fact that the advanced bases will always be protected to a greater or less extent by the strategical disposition of a superior fleet and therefore enemy attacks will not occur with such frequency and in such strength. For instance, a bombardment in force or an attempt forcibly to force entrance into a harbor by a large force when the waters are controlled by a stronger fleet will be extremely improbable. We have to deal only with harassing forces.
General Principles of Advanced Base Defense
In considering the artificial defense necessary for an advanced base it is well to keep in mind the following:
- The defense must be such as to leave the greatest possible mobile sea and air force free for its legitimate work: the destruction of enemy sea and air power.
- The primary object of the base defense is to prevent the enemy from damaging property within a certain area (anchorage, port facilities, etc.), not necessarily to destroy enemy craft. The defense required is only that necessary to render an enemy attack so dangerous as to be unreasonable, taking into consideration the conditions under which the enemy is operating.
- In order to simplify training and supply and to maintain mobility, the material used should be light standard Army, Navy or Marine Corps and be capable of the widest use.
- The defense considered must consist of the materiel which we now have or which we may reasonably be expected to have at the outbreak of hostilities.
Experience has shown that the best fixed defense against all types of sea and air power is generally good observation, quick communication and rapid, accurate gun-fire. The fixed defense should particularly concentrate on these three elements.
Surface vessels, submarines and aircraft may all be located either by sight or sound. By reason of the great speed of modern sea and air attacks and the utilization of cloud effects, thick weather, darkness and smoke in their execution, location by sound is becoming of extreme importance: in fact, warning of attack may not be possible otherwise.
Good observation in a base defense should, therefore, include a complete system of listening-in devices, as well as salient visual observation stations. Tripod sea-phone installations (or magnetic loop), aircraft sound locators (paraboloid, 1300-lbs.) and radio compasses should all be thoroughly investigated, types most suitable secured and the personnel trained in their use. It is understood that, by reason of methods employed and noise conditions, all listening-in devices installed on shore have much greater efficiency than those installed on or towed by sea and air patrol craft.
The principal factor in realizing a good visual observation system is the training of observers. The importance of this factor is seldom appreciated, and it is high time for a change in attitude. No man can be considered a reliable observer until he understands the best positions from which to observe under the various light conditions (including artificial light), how to use his glasses to search accurately and without undue eye fatigue, the characteristics of searchlights and flares, the natural characteristics of the various states of the sea and air, and the types and habits of possible targets (with methods of camouflage) during all the conditions of visibility.
Visibility conditions in the theatre of operations in question are only average, on account of prevalent clouds and rainfall. However, it is said that the sky generally clears toward evening, giving fair evening and night visibility, which is most important.
The peculiar reef and water conditions obtaining in the theatre of operations will doubtless also tend to lessen sea sound-locator efficiency, by reason of the chafing of cables over coral ground, and the difficulty of
securing suitable depths of water and resting ground for the tripod and other installations. Moreover, if suitable water and bottom is found it will probably beat the expense of lengthening or unduly shortening base lines.
To sum up: It is believed that "listening-in" devices are of rapidly growing importance in base defense and that no time should be lost in making arrangements for their use in future advanced base operations.
Communications for command, fire-control, observation, etc., should be by wire when possible, but always supplemented by radio, visual and sound systems. A sound system is absolutely necessary in case of attacks during darkness and thick weather. It is well to equip observation stations with machine or light guns for use against submarines and aircraft when sighted. By opening fire with tracer ammunition, the fact of sighting an enemy and his approximate location are instantly transmitted to the adjacent defenses. Within the restricted limits of a fixed defense, pyrotechnics and large dial shapes (with pointers to register bearings) will have their widest use in speedy visual communication.
The field telephone will, of course, be the standby. In addition to the land equipment, however, there should be provided a limited amount of submarine telephone equipment for use in linking up vessels, when necessary, and elements of defense located on detached islets. In the theatre of operations here considered the elements of the defense will always be more or less separated by water. Armored cable will be necessary on account of the coral bottom and strong seas and currents.
Radio equipment need not be very powerful but should be plentiful. It will be of great value in any case for communicating with ships and as a supplementary means to wire lines which will generally lead through jungle and thus will be difficult to protect from enemy fire and sabotage. It will be of particular value in linking up the islets of atoll anchorages. Needless to say that the islands occupied by mobile troops as emergency bases and for observation should be provided with radio. Equipment with a sending radius of about 500 miles would suffice for the more important stations and of 100 miles for the lesser stations. The distribution would, however, be such as to ensure complete communication throughout the area occupied. Considering the radio communication that may be required, at least 3 large and 6 small sets should be included in the fixed defense materiel.
But, however good the means of communication may be, true efficiency cannot be maintained without proper battle charts, communication plans and personnel trained in message forms. (How many Marines can, upon sighting a periscope, report briefly and fully the necessary information for best gun action, or accurately identify and intelligently report the movements of sea and air targets?)
In considering the number and calibre and location of guns, it is well to remember that when a ship hits a shore battery it puts out of action only what it hits, but that when a battery ashore hits a ship it puts out of action what it hits plus almost everything else; also that in close attacks it is not necessary to sink a ship in order to prevent its executing its mission, but only so to impede its movements as to cause a miscarriage of the attack. The proper use of searchlights and flares (to render navigation difficult) and of field and machine-gun fire may very well play a part in this respect. Searchlights are particularly effective in confusing air-pilots.
The gun defense should include guns in sufficient numbers and of sufficient calibre, or should be so projected, as to cover all base approaches and render hazardous any attempt to bombard or to closely approach the base area. Owing to the fact that the configuration of harbors renders uncertain the projection of guns, the gun should be as large as can be handled under the enforced conditions of rapid unloading and installation. This gun is considered to be the 7-inch gun, a number of which are now on hand. For the sake of economy and time, the main gun defense must consist of direct rapid-fire guns, preferably with tractor mounts, so emplaced as to be capable of all-round fire. Such guns can be installed quickly, become effective immediately and can be well served by simply trained personnel. These guns should be provided with alternate emplacements as a measure of security.
The number of guns required depends more or less upon the distance they are projected from the base area, the ease with which they may be masked and their possible arcs of fire. It is considered that under average conditions all water approaches to the base should be covered by at least four heavy-calibre guns. The mission of these guns is to resist all forms of sea attacks.
For the general support of the main defense guns, the covering of dead angles and the resisting of close attacks by submarines or by surface vessels which may attain close position by reason of adverse visibility conditions, a secondary close defense of lesser calibre guns (with the same characteristics as the guns of the main defense) is required. The work
of this defense might be performed by an increased number of heavy guns or by utilizing some of the heavy field artillery of the land defense, but not so efficiently. The likelihood of the close attacks above mentioned demands provision for a rapid, effective fire being delivered on short notice, which can only be done indifferently with the same weight and personnel in the alternative types. About a 5-in., high-powered, rapid-fire gun, preferably on a pedestal mount, is desirable for this use. At least four guns are required to command an entrance and its near approaches, the guns being sited particularly to cover water and areas well in advance of any mine or other barrier defense which may be provided. We should procure from the Navy and keep on hand a sufficient number of these guns for use as set forth.
Any additional gun defense against sea attacks (for instance, to cover defiladed water areas along the coast line from which enemy ships might conduct indirect bombardments) should be required from the artillery of the mobile land defense. We have now on hand a number of 8-inch howitzers, suitable for sea-coast defense in general, which would be satisfactory.
In the theatre of operations in question, sea defense guns will be required in unusual numbers by reason of the saliency of the anchorages and the numerous and sometimes wide passages in the anchorages of the atoll type, which probably cannot be securely barred with mines, owing to the swift tidal currents and the counter-mining operations of enemy sea and air craft. The ship, shore and terrain conditions of the atoll anchorages offer few difficulties to the landing and installation of sea defense guns, unless it be in the construction of emplacements owing to the lack of suitable material on the ground. Spongy timber or coral sand concrete can be used for the tractor-mount platforms, but pedestal mount platforms of timber or steel must be carried with the guns; coral and sand concrete cannot be depended upon except as anchor weight, and suitable platform lumber is not to be found on coral islets.
Considering the defense required as modified by the natural characteristics of the harbors under consideration, it is estimated that a minimum of twelve 7-inch and twelve 5-inch guns should be included in the fixed defense materiel.
The question of anti-aircraft gun defense is not very well crystallized at present. Many articles have been published recently, questioning the value of this defense, in which statement is made repeatedly that ten thousand shots are required to bring down one plane. There can be no doubt that some of these articles are simply propaganda to secure additional pursuit planes for the air services. In considering the value of anti-aircraft guns for an advanced base defense, the question is really not as to how many air attacks may be frustrated by ten thousand shots. As a matter
of fact anti-aircraft guns of present and probable calibre cannot prevent aircraft from attaining a bombing position, but, if in sufficient numbers and properly controlled, they can force the enemy to such a high altitude or compel him so to deviate from his course when lining on a target as to render the success of the attack very doubtful. This is what the antiaircraft gun defense of an advanced base should be in effect.
The idea being mainly to obtain a moral effect on the pilot that will cause him to worry over danger and thus distract his mind from his bomb projection, the fire should be made to appear dangerous and of uncertain system as well as having as much accuracy as the equipment will permit. This effect, it is believed, will be best obtained by surprise zone fire, the extent of the zone depending upon the number of guns available.
As to calibre, the tendency now is to increase to six inches primarily for high targets, lesser calibres being in support for resisting low bombers. Of course, the greater the calibre without loss of volume of fire, the better. In any case we must use the types supplied by the Army or Navy, preferably the latter.
The main anti-aircraft guns are generally employed in groups of six, well advanced (up to 10,000 yards from air-objectives) along the most probable air routes of approach, up or down wind, along roads, streams, coastline, etc.. The lesser calibre guns are normally emplaced in rear support of main guns to cover aerial sectors which the main guns cannot cover owing to grave danger to one's own personnel, materiel and shipping, and to resist the close attack of aircraft which may have passed through the first defense zones or approached unobserved by reason of adverse visibility. In case of shortage of guns, or when strafing is to be expected, the anti-aircraft defense should be supplemented by the heaviest-calibre machine-guns available, sited at least burst-beaten-zone distance away from air objectives.
As the effectiveness of an adequate air defense depends upon the efficiency of the fire control, every effort should be made to perfect it, especially for the fire tactics to be used.
In the theatre of operations under consideration the terrain adjacent to anchorages does not permit of an y extended projection of guns from the area to be protected, thereby necessitating a greater number of guns than might otherwise be required. Considering the extent of the anchorages, as also the lack of communications, it is believed that no less than 24 guns of largest calibre, supported by 12 of the same or lesser calibre, would be required under ordinary conditions. As communications will be lacking and as fixed guns permit of better fire control and more accuracy of fire, these guns should be provided with fixed mounts.
Both the sea and the air defense must be supplemented by artificial light: searchlights and star-shells. The latter, which are being developed for all Navy secondary batteries and anti-aircraft guns, will be a valuable supplement to the searchlight defense and may, when they are fully perfected, replace it in part. At present their action is limited to about 3000 yards and beyond (a low velocity being necessary to ensure functioning of the parachute). It is believed that these shells, in themselves, afford sufficient illumination of water areas outside of their minimum limit (3000 yards) and that the searchlight equipment need not necessarily be of greater power than is required to illuminate targets efficiently up to that range. In determining the calibre of fixed defense guns and their siting, the function of shell illumination should be considered.
The sea searchlight defense, to be adequate, should cover thoroughly all water approaches and barrier defenses. The normal allowance would be one searching light, one battle light and one belt light for each battery group--or a distribution that would ensure a searching light, at least one battle light and a belt light being in readiness for action on any targets that might approach. The light control and tactics are all important in order to ensure continuous searching of all areas, to avoid dead angles, and to ensure the battle illumination of all targets which maybe spotted.
If star-shell illumination proves as efficient as expected, a modern 30 or 36 inch light should be of sufficient size. These, being mobile, should be provided with alternate emplacements as a protection against special attacks which might be made against them preparatory to a night attack in force. The distant automatic control of lights is desirable if it is reliable and does not require a too delicate or too bulky apparatus.
Floating flares, anchored in advance of barriers, when fired, form an excellent auxiliary light defense against blocking or other forms of close attack.
Air-defense lights must be both plentiful and powerful (say 36-in. or over). As a rule each battery should be provided with at least two lights: one pilot light (direction indicator) and one (preferably two) searching lights. They should be emplaced on the flanks of batteries in such a manner as to cover the sky within 30° of the horizon. The searchlight, gun and pursuit-plane air defense requires very careful planning and training with regard to control tactics in order that each weapon may function properly. The searchlights should be supplemented by star-shell illuminations.
In the siting of searchlights particular care must be taken to avoid their forming a location point for the targets they are designed to protect and to ensure the best observation of the target by observers and gunners. Low advanced positions on the flanks of batteries or observation stations are considered the best. In the theatre of operations in question, the siting of searchlights will be particularly difficult owing to the general saliency of the harbors and the restricted land masses of the atoll anchorages. These disadvantages can only be compensated for by furnishing sufficient lights so that they may be used in various combinations, or possibly by constructing a large number of alternate emplacements.
Considering the dispersement of batteries (both sea and anti-aircraft) that will be likely, a minimum of 18 searchlights, medium or larger calibre, would be required.
A mine barrier defense is very desirable under conditions which may permit of submarines or surface vessels approaching unobserved close to a harbor entrance in readiness to run by or permit of submarines approaching and passing through a harbor entrance while submerged. The general custom heretofore has been to close harbor entrances with observation mines, except for an echeloned passage left free for one's own craft. However, conservation mines require such a vast amount of equipment and numbers of trained personnel to ensure their effective use that their inclusion in an advanced base defense has always been considered in the light of a necessary evil. Added to these disadvantages there was also a decided premonition of danger to our own ships (considering the type of mine available and the haste necessary in laying it). During the World War the Navy developed a type of defensive contact mine which proved effective against both surface vessels and submarines within operating depths. This mine (300-lbs.) is fitted with antenna extending 60 feet above and 100 feet below and can be laid in depths of at least 1000 feet. A number of vessels have been equipped with apparatus for laying this mine, and it is intended hereafter to have such vessels lay such fields as may be necessary at an advanced base. This type of mine field will probably have a straight-away passage for ships which must be considered in arranging the gun defense.
Owing to the strong tidal currents prevalent in the entrances to the anchorages herein considered, effective mining may be somewhat difficult, these currents not only causing uncertain displacements of the mines in depth but also causing them to drag anchors unless the latter are unusually heavy. In many cases it will probably be found that gun defense alone must be relied upon. Also it will be impossible to project the mine fields very far in advance of the anchorages on account of the great water depths close off the reefs.
Since the development of bombers, a mine field gun-defense to prevent counter-mining must be considered in locating anti-aircraft guns as well as in locating the guns of the sea defense.
An effective type of barrier defense against torpedoes which maybe fired through the harbor entrance from the outside is not known at the present time, the ordinary torpedo net being often ineffective against torpedoes fitted with cutters.
A boom and possibly net defense to prevent the running-by of floating mines on currents may sometimes be necessary--especially under the conditions obtaining in the theatre of operations under consideration. A simple boom defense may be improvised on "location." Where mines can be observed, they may be destroyed by gun-fire.
Total Fixed Defense Required
Radios: 500 miles radius (average conditions) 3 100 " " " " 6 Guns: 7-In R.F. Gun, tractor mount 12 5-In R.F. Gun, pedestal mount 12 A.A. Pedestal Mount} interchangeable 24 3-In. A.A. Pedestal Mount} 12 Searchlights: 30-In. and 36-In. 18 For the sake of general economy this defense should consist only of that land aircraft necessary for the immediate security of the base; any water aircraft required under special circumstances being supplied by the Navy as in the case of the mobile sea defense. Land machines based on land are more efficient for the work required than either water machines or land machines based on carriers, on account of the comparatively restricted and slow maneuvering powers of the former and the comparative slowness and greater liability to accident in getting under weight from the latter. Moreover the diverting of water machines and carrier land machines from their primary duty of fighting enemy sea and air power in blue water areas to purely defensive work at a base is not only wrong in principle but very uneconomical.
Mobile Air Defense
The duties of the mobile air defense at an advanced base are threefold: to observe, to bomb, to pursue. At an average advanced base these duties would include the following:
- Ensure a continued observation of the harbor entrance or entrances and approaches for enemy submarines and other craft within a radius of 20 miles during daylight;
- To ensure at least one hour's warning of any surface attack on the harbor or coast-line during daylight;
- To resist ordinary sea-raids and landings by bombing enemy vessels and observing our own gunfire at any hour;
- To supplement the anti-aircraft defense in resisting enemy air attacks by engaging in combat with enemy bombing and pursuit planes, especially the former, at any hour.
The fewer the types of planes necessary for the performance of the functions outlined, the better, as in the case of all advanced base materiel, and it is the present policy of Marine Corps Aviation to hold the number of types down to two if possible: one for observation and bombing and one for air-combat (pursuit planes).
The number required of each type will depend principally upon the enemy building program and the probable strength of the enemy attacks. Considering the probable operations in Micronesia we may expect sea attacks by auxiliary craft and air attacks in comparative strength considering the total strength of the enemy. In the ordinary small island or atoll anchorage, the functioning of the aircraft would require at least three scout-bombers being in the air throughout the day, or, with reserve, a total of 12 machines. To resist enemy sea attacks during day or night, there should be available at least 12 more bombers. For aerial pursuit (combat) of enemy planes, there should be at least 24 planes, the least number that could be expected to break through the enemy pursuit plane escort and inflict damage on his bombing formation. We thus have as a total mobile air defense: 24 pursuit planes and 24 bombers. This defense has already been arranged for by the Marine Corps.
The question of landing facilities may be rather difficult in the theatre of operations under consideration, as the only natural landing fields seem to be reef encircled beaches and high mountain plateaus. A field at least 30 by 500 yards, with borders formed of high vegetation and extending preferably in the direction of the prevailing wind, and a surface permitting of the unobstructed running of an automobile at the rate of 40 miles per hour, is required. Occupying troops must in all cases be prepared with tools to put landing fields in condition for use.
When the advanced base fixed and mobile air defense does not effect the degree of security desired on account of natural harbor characteristics or other reasons, a mobile sea defense as needed must be assigned to supplement them. Needless to say, this defense must be as small as possible consistent with the security necessary and must be composed of craft least valuable in the fleet operations--units which have undergone hard service or have suffered war damage. The defense would normally consist of the following types:
Mobile Sea Defense
- Patrol boats with light guns, anti-aircraft guns and depth bombs;
- Mine sweepers;
- Destroyers, submarines and aircraft assigned for counter-attack work.
The main object of the land defense is to protect the base sea and air defense, which, in turn, protects the base facilities, and to cover any enemy objectives not covered by those defenses: defiladed bombardment positions, natural aircraft landing-areas, etc.
Mobile Land Defense
If it is the intention of the enemy to capture the harbor for his own use, it will be necessary for him completely to reduce, with infantry, all defenses that bear upon the harbor and its approaches. If the enemy's intention is only to destroy materiel in and around the harbor or to deny the use of the harbor to our fleet, it will be only necessary for him to secure and maintain a position on land from where siege gun fire can be brought to bear on the base area. Siege guns of a suitable type may be used effectively at a range of ten miles. Therefore, in the case of small island positions, an enemy might have to advance only a short distance inland in order to carry out his mission. For these reasons, together with the fact that in all cases the coastline will be unusually favorable to the defense and unusually unfavorable to the offense, the governing factor in the land defense of any island position (at least up to 500 square miles in area) should be the necessity for preventing a landing.
But, while the main line of defense should follow the sea coast, a most stubborn inland defense should be provided for; the enemy being forced to take successive secondary and switch lines and finally a stronghold. The latter should contain elements of the fixed defense bearing on the harbor and approaches so as to deny the latter to the enemy and maintain a foothold for recapture to the last.
In view of the foregoing considerations, the ordinary system of land defense would consist, in the main, of a first line (line of resistance: seacoast), occupied in force; a second line ( land-line enclosing base facilities and sea and air defense), and a stronghold (enclosing certain elements of the fixed defense); the latter two lines being occupied in force only in event of the defenders being forced to retire from the line in advance. A detailed outline of this system follows:
This line follows the seacoast and defends all possible landing places; and it should be planned regardless of weather or sea conditions at the moment. The disposition of armament and personnel should be made with the following objects:
To attain the objects outlined, the first line should consist of the following elements:
- Hold the transports off as far as possible, thus delaying the ship-shore transport of troops;
- Bring artillery, 37-mm and machine-gun plunging fire to bear on boat formations to inflict personnel losses and to disorganize formations;
- Bar the advance of the small boats inshore by water obstacles and the advance of troops inland from the beach by land obstacles;
- Deliver surprise fire of all arms on troops at water and land obstacles, or, in the absence of obstacles, when troops are disembarking from small boats and forming for the advance inland;
- Contest the advance inland by counter attacks and the defense of switch lines on the flanks of landing places (necessary to covering forces of the enemy);
- Protect the defenders against enemy sea and air supporting fire; and
- Ensure a safe retirement of the defending force to rear lines in the event of necessity therefore.
- Line of water obstacles. These should consist, preferably, of wire or cable entanglements, held in place by wooden or iron stakes and natural protuberances such as rocks, coral heads, etc. Their
anchorages should be sufficient to resist the bucking of power boats and thus force the disembarkation of troops. They should be well advanced and of a height (depending upon local beach characteristics) so that they would prevent the passage of boats but yet be covered at that state of the tide most suitable for landings.
- Line of beach obstacles. These should be constructed of wire or material at hand and be located on the back beach where concealment may be possible. Extending at various angles to the rear, light spur lines of obstacles should be constructed so that the enemy may be unconsciously guided into prepared defensive zones of fire. (The Germans employed this system at Blanc Mont Ridge and, so far as known, none of the Marines advancing realized it.)
- Line of observation posts and patrols with searchlights, beach flares and pyrotechnics. High and low positions for searching under various light conditions should be provided for. Beach flares and pyrotechnics, and infantry lights (up to 12 inches) would probably suffice in most cases; if not, the type of light used by the fixed sea or air defense should be used.
- Line of machine-gun and 37-mm nests, permitting of plunging fire towards the sea and flanking the beaches and approaches to desirable enemy covering positions. If located on high projecting spurs, both high and low positions should be prepared; the former being used against troops in boats and the latter after they strike the beach.
- Line of sector supports or counter-attack troops (infantry with special weapons) to meet the enemy with grenade fire on the beach and to execute counter-attacks. The supports should be located in nests or fortified posts echeloned in rear of and supporting the line "(d)" and defending desirable enemy covering positions.
- Line of field artillery positions from which an effective fire may be brought to bear on transports or small boats, obstacles, the beach and the fronts of infantry positions. The position of these guns will depend upon the terrain and existing communications. At times they should be pushed practically to the beach.
- Line of sector reserves or counter-attack troops (infantry with special weapons) having the same general mission as the sector supports, so located as to be able to counterattack before the enemy has taken or consolidated his covering positions.
- Line of heavy artillery positions (director indirect fire) to be used primarily against transports and other sea targets and secondarily against the targets named for the field artillery in (f).
- Grand reserve of all arms, so located as best to support line of sector reserves, or cover retirement of advanced forces and occupy rear lines as necessary.
The distribution of forces in the defense will depend upon the physical characteristics of the terrain and waters adjacent thereto and the following considerations: (1) The forces necessary for the initial defense of the various landing places in case the enemy attacks under favorable conditions; (2) the time necessary for the support and reserves to act; and (3) the provision of reliefs for the forces in permanently occupied positions.
These lines should be prepared for defense on the same principles as the First Line. The location of the second line should ensure~if possible, that damaging enemy gun fire cannot be brought to bear on the more important parts of the base area.
Second Line and Stronghold
These supplementary defensive lines (connecting the main lines of defense at intervals) should be prepared for the following objects:
- To isolate the base area from any outside landing places. (The second line may ensure this condition.)
- To isolate the various landing places from each other, thus preventing the junction of enemy forces and permitting of his defeat in detail. At any landing place the switch lines and rear line which they join would normally coincide with covering and advanced positions desired by the enemy.
- To delay the general advance of the enemy at strong natural defensive positions.
The foregoing outline of land defense organizations can seldom be adhered to completely, not only on account of natural conditions imposed but on account of the lack of time. However, the fact that it is expected to occupy the base only for a short time or that there will be insufficient
time in which to carry the work to completion MUST NEVER BE MADE AN EXCUSE FOR NOT CONCENTRATING EVERY EFFORT AND UTILIZING EVERY MOMENT TOWARDS MAKING THE DEFENSE AS STRONG AS POSSIBLE. Enemy attacks in unexpected strength and unexpected reversals to our own forces may always occur.
In the case of the theatre of operations under consideration the natural restrictions imposed at available base anchorages are rather extreme. The configuration and isolation of the coral atoll land patches enforce practically a beach line defense by all arms and render impracticable inter-element support. Troops must fight in position and therefore the personnel and materiel should be that capable of resisting any likely enemy concentration on or near the beach. On account of the close proximity of base facilities to possible landing places, surprise raids, especially at night, will be likely. The best answer to enemy attacks under these conditions would be checkerboard strong point defense, combined with intricate obstacle construction from the beach line rearward.
At the outset, at least, conditions will be practically the same on the volcanic islands, owing to their rough jungle interiors and the lack of trails and roads. Troops and materiel for the defense will have to take position by sea and establish depth inland so far as the military situation demands or time and terrain conditions permit. Trails may be out for the use of infantry supports and reserves, but their action will be slow in any case. Artillery once placed in position inland will ordinarily fight in place throughout any operations. The mobility of the defense will depend wholly upon the roads which they build themselves. The use of water transportation for supporting troops during an action would be generally hazardous whether inside the barrier reefs of the volcanic islands or in the lagoons of the atolls.
Considering both the atoll and volcanic types of anchorages and the extent of their land masses, the usual sea and weather protection obtaining, the fact that not over fifty per cent of the coastline would be suitable for landings, and that the defense must practically fight in position, one arrives at the following conclusions as to the minimum armament required for the mobile land defense:
32 75mm. field guns (partly landing regiment materiel);
18 155mm. field guns*
12 8-in. howitzers*
8 medium calibre (38" searchlights*
(*Defense regiment materiel)
32 small calibre (12" to 18") searchlights, partly landing regiment materiel;
6 field radio sets, 100-mile radius, landing regiment materiel.
The Marine Corps has most of the above materiel on hand at the present time.
Always in considering the reduction, occupation and defense of advanced bases one is struck by their utter lack of local resources, not only of a military nature but of any kind. However, if these resources were present to a considerable extent at any point, an enemy would probably include that point in his main defense and it would not be available to us as a base. The suitable bases in the theatre of operations under consideration form no exception to the above rule. Rough timber, rock and small boat transport are the only resources of importance. The forces of occupation must provide the usual living facilities as well as a military defense. For this work, men with engineer training are needed in unusual numbers. In order even to start work, we must construct landing facilities and roads, and that work must be followed by an unusual amount of blasting, excavating and clearing.
Auxiliary Defense--Personnel & Materiel
Being dependent upon a successful landing in every case, and, after landing, being dependent upon water transport (except for land transport on the few roads which we ourselves may build), personnel trained to handle small craft (motor, sail or oar) will also be badly needed.
An unusual number of signal troops with equipment will also be necessary on account of the abnormal isolation of defense elements by thick terrain and by water passages.
In sea operations special organizations employed only as such must be as small as possible. Personnel may be given special training for emergencies without withdrawing them from fighting organizations.
In regard to auxiliary materiel or equipment, there has been in the past a tendency to overload with many articles neither necessary nor serviceable. Delicate or complicated equipment or that of special, limited use should not be included in advanced base materiel provided the service necessary can be approximately obtained otherwise. Only such equipment as can be reasonably depended upon to withstand rough handling, exposure to the elements and service by ordinarily trained personnel should be included. Whenever unusual equipment is added, weight, time-saving qualities and reliability in service should always be carefully considered.
Advanced base land transport is an item which deserves particular mention. In the operations set forth, it will be noticed that nearly all troops and defenses will be located near the sea coast and will fight practically always in position. The fact that there is ample small-boat transport and that they can be supplied by reef-bound water routes and that roads are now and will be very few, forces on[e] to conclude that land transport
will be of limited use. Not over 50070of the motor transport ordinarily required for the supply of mobile troops and movement of mobile guns and other units need be furnished.
Owing to the lack of local resources, all materiel and equipment absolutely necessary for the installation and maintenance of the military forces should be carried on transports. Among the items of importance are: Tentage, tarpaulins, water-containers for the storage of rain water, cement, construction railway, engineer tools and explosives, line and tackle, barbed wire, sand-bags, timber-working tools, wire net for camouflage, draft bolts and heavy spikes for dock, bridge and bombproof constructions, etc.
[B L A N K P A G E]
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