The Reduction of the Islands
The theatre of operations, with its checkered inter-supporting island groups, defended and used as bases for the projection of sea attacks, presents in its reduction much the same problem as do modern deep defense lines on land. The reduction of a single group and the projection of our fleet thereinto would be analogous to the assault and occupation of a single center of resistance, thus subjecting the holders to concentrated attacks from both sides. Therefore, the proper procedure would be to reduce all groups in any defined sea area, or line, simultaneously; the limits of any objectives, including, if possible, base facilities for the pursuance of our operations in areas beyond.
Base facilities for our fleet require an anchorage of such extent as can be found only in the atoll lagoons. On the other hand, if proper facilities are to be provided for light craft, a volcanic island anchorage should be available. The ideal sea objective would be one which included an atoll anchorage for the fleet with a salient volcanic anchorage for light vessels.
The seats of local government and the principal centers of population and trade are located on volcanic islands, with the exception of those in the Marshall Islands, which are all of the atoll type. Enemy bases will also probably be located in volcanic islands. In any event it will be necessary to reduce and occupy them in considerable force whether we use them as bases or not.
In view of the foregoing, the reduction of the theatre of operations would naturally divide itself into a series of phases somewhat as follows:
First Phase: Reduction of the Marshall Islands, if possible, plus Kusaie Is., or Ponape Is., or both; Second Phase: Reduction of the Caroline Islands west to, and including, the Lamutrek group; (if possible, Yap Island); Third Phase: Reduction of remainder of Caroline Islands, and Yap and the Pelew Islands.
Of course, the exact extent of objectives will be determined, more or less, by the resistance to be encountered at the time of reduction. It is very desirable that we reduce the volcanic salients of Kusaie and Ponape during the first phase, although the resistance at these points may be such as to force us to make their reduction an entirely separate phase. It is also very desirable that we take Yap Island in the second phase, owing to its relative position with regard to Guam, which, it is expected, will be strongly held by the enemy as a base.
For the sake both of economy and efficiency, the plans for the reduction of a sea objective should take cognizance of two types of operations, viz:
- Special Objectives: Those points where special resistance is to be encountered--as at enemy bases and at those which we intend to use as bases.
- Occupation Objectives: Those points where little resistance is to be encountered and our object is merely one of occupation, search, observation, police, and denial to the enemy.
The best troops and facilities should be assigned to special objectives and the forces should proceed direct and attack at all necessary points in force. The occupation forces should be assigned sub-sectors (or groups) and proceed to occupy and search out the various islands; not necessarily simultaneously, except that they should begin operations in their respective areas at the same time.
In effecting a landing on any type of island, or island groups, it is always best to land or make feints at landing, at several points, the relative position of the latter depending upon the ease and celerity with which the forces can join in a common movement after landing. These tactics confuse the enemy and lead him to disperse his resistance.
It is to be expected that we shall encounter strong resistance in the volcanic islands (Kusaie, Ponape, Truk, Yap and Babelthuab) which have strong natural defense characteristics and are of particular value to the enemy. This defense will, at least in some cases, be regularly stacked up from the coastline; generally in accordance with the following plan:
- Beach and reef obstacles;
Atolls have not the naturally strong defensive characteristics of the volcanic islands. If "stacked up" with a regular defense, the string of keys around the lagoons will form, in effect, a line of redoubts, supporting each other, when possible, by machine gun and artillery fire. The defense of each key will be laid out on the same plan as that outlined for volcanic islands, except that, on account of its small area, special provision will be made for a stronghold (enclosed redoubt) of greatest possible strength.
- Coastal patrols and observers, searchlights and flares;
- Line of machine-gun nests, supported by infantry with special weapons;
- Line of sub-sector supports (counter attack troops), infantry, machine guns, field artillery;
- Line of sector reserves; infantry, machine guns, field and heavy artillery;
- Grand reserves, all arms.
In the case of either type of island the enemy will be at a disadvantage in the movement of his supports and reserves; this on account of the generally poor communications in the jungle-clad volcanic islands and the water passages in the atolls. This will result in the mass of the enemy troops being practically on the beach to meet an attack, but it will, on the other hand, enhance our chances of effecting a superiority at any given point.
To effect a landing under the sea and shore conditions obtaining and in the face of enemy resistance requires careful training and preparation, to say the least; and this along Marine Corps lines. It is not enough that the troops be skilled infantry men or artillery men of high morale: they must be skilled water men and jungle men who know it can be done ‹ Marines with Marine training.
Landings can be made over the barrier and fringing reefs in good weather, especially on the lee sides of islands; more often, however, weather conditions prevail that force landings through the reef passes.
In the case of atolls it is doubtful if all of the keys will be occupied, thus allowing of a more or less free boat passage within the lagoon; but, even if occupied, in most cases passages will be found which are not directly covered by enemy fire and through which an entrance can be forced. Once
inside the lagoon, all keys occupied by the enemy should be attacked simultaneously so as to limit enemy inter-supporting fire to the minimum. The extent of some lagoons will permit of troop ships entering and disembarking troops inside, if navigation hazards and enemy mines do not prevent. It should be done if possible.
In the case of volcanic islands there is a natural landing obstacle in addition to the reefs; the mangrove belt with its narrow tortuous waterways (which may be easily closed) with bottom of black mud. When the mangrove belt does not exist, the landing conditions are practically the same as those in Guam. The best procedure would be to land at high tide on the lee side in fair weather. Stretches may be found where the fringing reef is unusually low and where the mangrove belt does not exist. If an open coast landing is impossible, then the reef passages to land indentations must be forced.
There are two peculiar water hazards which may be met within landing on a coral coast, which are worthy of mention. They are:
- Lagoons formed by depressions inside the barrier reef or inside the outer edge of the fringing reef, and
- Lagoons formed by the forcing of underfit (sluggish) rivers along the beach, through the action of the sea in throwing up an ever lengthening sand bar at the river mouth. When a freshet comes in, the river breaks directly through the bar and the water backs up in the former bed, thus forming a lagoon parallel to the beach front. The process is repeated over and over.
The extent of the hazard (a) may be developed by peacetime reconnaissance, but that of the hazard (b) can only be determined by land or air reconnaissance at the time of landing.
In addition to the physical features of the coast, the choice of landing places will also be governed by the clearness of the approach for transports, the probable enemy resistance to be met with, and the relative position of ultimate land objectives.
The greatest elements of success in effecting a landing are surprise and rapidity of execution. The former generally depends upon the latter. From the time the transports start to position there should be no delay until the "boat-head" is occupied and consolidated. The movements, ship to boats, boats to beach and beach to covering objectives, must be continuous. The practice of delay in making up tows, occupying positions on the beach and shifting of troops on the beach must be eliminated. Most
important: quick offensive action from the beach inland not only confuses the defense in general but the counter-attack forces in particular.
The question of the time of landing is most important. The approach of the transports to position should undoubtedly be made under cover of darkness, and ordinarily the landing should be made at daybreak, so as to permit of the fullest use of all weapons and give the landing force a full day in which to pursue its operations on shore. Night landings in force are dangerous unless the coast conditions and the enemy defenses are well known. Small parties, however, might go ashore at night for the purpose of seizing positions preparatory to a landing in force, provided there is small chance of discovery. In this connection the matter of the use of smoke screens in effecting landings must be considered. Theoretically, the use of smoke except as a purely defensive measure is incorrect if it neutralizes the use of weapons with which the attackers have been particularly trained. That is, while it may well mask the attackers from enemy supporting forces, it should never mask the enemy being attacked from the attackers--the best defensive of the latter being the unhampered offensive of their weapons. We may conclude then that a smoke screen over the transports during the disembarkation of troops and over small boat formations until near the beach is good tactics, provided it can be controlled and does not materially interfere with the fire support of escort ships and aircraft and leaves the beach and its background clear to view. This would normally restrict the use of smoke screens to occasions when there is either an offshore wind or no wind. It may, however, be used well to the flanks with an inshore wind, if it is desired to obstruct distant enemy observation.
Great care should also be exercised in the use of gas, in order not to hamper the action of our troops after landing. As a rule, its use would be restricted to hindering the action of enemy supporting troops in areas through which we do not intend to operate.
The principal dangers to transports will be mines, torpedoes, aerial bombs and artillery fire. As a rule, deep water (too deep for mining) extends close up to the fringing reefs, and barrier reefs if present. If the barrier reef lies far off the coast, however, and it is necessary for transports to proceed through reef passages to the landing points, the passages may have to be cleared. The probability of torpedo and bombing attacks depends considerably upon the rapidity with which the troops are disembarked; that is: the time during which the enemy is permitted to act. However, escorting destroyers and air craft may be counted upon greatly to neutralize torpedo and air attacks and the sea demonstrations against enemy bases to hinder the action of both torpedo and air craft in general. As to artillery fire, it is probable that the further the landing point is from the main sea base of the island, the fewer will be the guns which can be brought to bear on transports. Such as are present may be more
or less neutralized by special fire from escort vessels, or, if the artillery fire is especially dangerous, the disembarkation of troops into small boats may be carried out beyond artillery range.
The first land objective is a "boat-head," which, like a "bridge-head," is essentially a covered stretch of masked shore line. The attainment of this objective will enable us to land our entire force with the least loss and fight the enemy on equal terms. The ideal "boat-head" would be a retired beach with high flanking spurs and rear heights located within good striking distance of the ultimate land objective: enemy sea-base and troop-center.
In working out preparations for a landing, the following particular points must be carefully considered and provided for:
- Preliminary Reconnaissance: This should be by air, this method being the most efficient, and its execution not necessarily leading an enemy to expect a landing.
- Land Objectives: The limits of the "boat-heads" should be clearly outlined by terrain features visible from the sea.
- Land Sector Boundaries: These boundaries should be clearly outlined by landmarks on the beach and inland, visible from the sea. They not only serve as a guide for troops after landing, but for small boats in the approach; boat formations may be more or less "messed up" and troops should fight in the sector in which they land, no shifting of troops on the beach being permissible during the first stage of the landing, It is the function of rear lines to rectify errors in distribution.
- Disembarkation from Transports: This plan should provide for troops leaving transports as rapidly as possible, the integrity of units in small boats and the proper order of troops in tows.
- Boat Formations: The formation provided should be that which is least vulnerable to probable enemy fire (artillery, machine guns, 37mm, aerial bombs) but at the same time permit of the placing of adequate forces on the beach without confusion of boats or troops. The following formation or a modification thereof would ordinarily be used:
Successive Lines of Tows:
Two waves of tows, each tow composed of not over 3 boats with 25-yd. interval; the tows in each wave at least 100-yds distance
(depending upon the number of men in each tow; the interval between waves of tows at least 50-yds, the tows of rear wave in rear of intervals of those in front wave.
Second and Successive Lines
The same general formation obtains as in the first line; interval between lines about 300-yds. The approach being partially covered by the fighting of the first line on shore, tows maybe heavier and distances and intervals decreased.
- Troop Formations on Shore: Considering the probable enemy fire, the action of his counterattack troops and the usual thick vegetation back of the beach, the dash from boats to cover and then on to the covering objectives should be made in waves of combat groups.
- Composition of Landing Force and Its Weapons: Infantry with special weapons, machine-gun troops, field artillery, pioneers and signal troops should be included. Power boats of tows should be equipped with 37mm and machine guns for use on the beach in approach. The infantry should be well supplied with rifle and hand grenades, particularly for use in clearing the beach just prior to and during disembarkation from the boats and in mopping up machine-gun nests. Pioneers with wire-cutters, bolos and explosives must be at hand for breaking up obstacles.
- Aerial Support: This should include reconnaissance prior to landing, and pursuit of enemy planes, observation, and strafing afterwards. The observation and strafing of enemy counter-attack troops and machine-gun nests is of particular value to the landing force in the initial fighting.
- Ship Support: If possible, the supporting ships should take position on the flanks of the landing force, so as to sweep the beach and the flanks of projecting spurs and to enable the landing force to approach close to the beach before fire must cease or be raised. Special fire objectives (counter-attack troops, batteries, machine-gun nests, and obstacles) and fire zones for searching fire, ending with a box barrage, if practicable, should be assigned. A battle chart should be prepared for designating fire zones and special fire targets, or at least arrangements perfected whereby targets may be designated by transmitting bearings and ranges from prearranged reference points.
- Communications: A careful and complete plan of communications must be provided. Immediately upon the landing of the 1st line, shore headquarters should be established, communications
opened up with the sea and air forces by pyrotechnics, flags and radio, and "drop message here" stations and available landing fields marked. These measures must be taken at once if the full value of ship and airplane supporting fire is to be obtained. Intercommunication between units of the landing force would be principally by pyrotechnics and runner until field telephones were advanced.
- Administrative Measures: Provision should be made for a prison pen on the beach and for the transfer of prisoners on board ship as soon as they are examined. The beach space should be organized and the landing points for reserve and special troops and for materiel and supplies plainly marked with large placards or flags.
Upon the occupation of any enemy territory, the forces of occupation must proceed immediately to carry out the following measures:
- Capture and confine all enemy troops and civilians and all pro-enemy natives;
- Search out and take over or destroy enemy base facilities, particular attention being given to hidden fuel depots. (The vast number of native boats capable of inter-island traffic, together with trading schooners of shifting nationality, renders the secret supply of fuel very easy unless all islands are carefully searched out and observed.)
- Seize native water-transport required for the forces of occupation and arrange for the necessary native personnel to handle it.
- Establish provost organizations to ensure thorough police.
- Publish and explain to native population a proclamation of occupation.
If the island or group occupied is to be used as a base for our sea forces, the installation of the fixed defense and mobile land defense should be proceeded with at once and with maximum effort.
In the case of island groups occupied for denial to the enemy, as an emergency base of operations and information for us and for the police of the inhabitants, it may not be necessary that all islands be occupied by troops in place, but that (for instance) a garrison be established at
the main protected anchorage, trading post or seat of local government, and the remainder of the islands be patrolled by combat groups in native boats. These groups of islands, by reason of position, are in reality outguards for the fleet bases and the troops have a fighting function of observing and reporting enemy movements in addition to denying the groups to enemy use and holding them for our own.
In view of the foregoing, the forces of occupation of such groups should be charged with carrying out the following particular measures:
- Clear and mark landing fields or areas for land and sea planes.
- Establish "Drop Messages Here" ground; erect signal and observation tower; install radio.
- Seize and segregate native water transport and personnel required for inter-island patrol and for supply.
- Construct palisade redoubt (masked from sea) enclosing or covering the facilities named in (a), (b) and (c), adjacent boat passages and landing places, and as much of the inhabited portion of the island as possible. Provide storage space in redoubt for ammunition, food, water, fuel and other supplies. Machine-guns and several pieces of artillery should be provided for these posts, guns to be sited inside or out, as conditions demand.
To arrive at the fighting forces required to take a sea objective, let us take a concrete case. We will presume that the enemy has occupied the Marshall Islands with auxiliary sea- and air-craft and land troops in force; that he has "stacked-up" Wotje Atoll (the best anchorage salient to our approach) as his principal base; that he has "stacked-up" Eniwetok and Jaluit Atolls (the best anchorages salient to himself and most suitable for the use of our fleet) for use as emergency bases and to deny them to us; and that he has occupied the other anchorages with sufficient troops and mine defenses so as to forbid our use of their passages and anchorages without landing and sweeping operations.
Reduction Forces Required
In other words: The enemy has stacked-up the sea objective with military strength of little or no in a fleet action, to force us to subject our fleet units to the attacks of his auxiliary craft for the greatest length of time and under the best conditions for himself.
We have the following missions to perform:
- Primary Mission: To secure a suitable base (Eniwetok Atoll for instance) for the fleet and project it therein with the least danger and as soon as possible after its approach to the theatre of operations.
- Reduce the enemy base;
- Reduce the enemy emergency bases: those denied to us;
- Reduce all other anchorages which the enemy might use as emergency bases.
We might first concentrate on the primary mission and, after its attainment, proceed to the execution of the sub-missions; but this, however, is exactly what the enemy would wish us to do, permitting, as it does, his concentration on our fleet action units, with all his bases available for the projection of his attacks. We should therefore endeavor, by the use of our land troops and auxiliary craft, to contend for immediate control of all parts of the sea objective at the outset, thus removing the advantages held by the enemy, gaining them for ourselves and befogging the enemy's mind as to the movements of our fleet in general.
Our action must be to drive in force simultaneously on a base for our fleet, the enemy's base and his emergency bases (denied to us) and begin the occupation of the other groups. Considering the geographical location and military importance of the groups to be reduced, we may properly divide the sea-objectives as follows:
Sea Objective: Marshall Is.
- Eniwetok--Ujelang Atolls;
- Wotje Atoll;
- Jaluit Atoll.
- Mine- Arhno--Majuro--Aurh--Maloelab Atolls;
- Likieb--Ailuk--Mejit--Taka--Utirik--Biker--Taongi--Rongerik--Rongelab--Ailinginae--Bikini Atolls;
- Elmore--Namu--Lib--Kwajelinn Lae--Ujae--Wottho Atolls.
In the reduction of an atoll any one of the following missions may be the immediate one, depending upon the general strategical and tactical conditions:
- Occupy land masses necessary to control landing fields and anchorages and thus prevent their use by the enemy;
- Occupy land masses necessary to control landing fields, anchorages and passages thereto, thus permitting their use by our forces;
- Occupy entire atoll for our unrestricted use and entire denial to the enemy for any purpose whatsoever, including observation.
When the reduction forces are limited in strength the operations would, as a rule, be carried out by phases in the order named, provided enemy resistance and natural landing conditions permitted (for instance, it might be necessary to first attack and occupy keys flanking a passage in order to obtain access to a lagoon).
In the reduction of any key of an atoll, the covering position to be attained will be the key itself, or at least a water front hooked up with one or more short flank lines. The landing will entirely succeed or fail practically on the beach.
The minimum forces required to take the various objectives named above are those necessary to:
Special Objective (1): Ensure without fail in a single phase the reduction of the entire atoll of Eniwetok, our intended fleet base.
Special Objectives (2) and (3): Ensure the reduction, in the first phase, of the land areas controlling the passages and anchorages of Wotje and Jaluit Atolls.
Occupation Objectives (1) and (2) and (3): Ensure in the first phase the denial to the enemy of the passages and anchorages in the atolls of greatest relative military importance, the control of the remaining atolls being secured in order of relative military importance.
In view of what has been stated regarding the tactical employment of personnel and materiel and in order to make a simple and intelligent statement of forces, it is deemed necessary to cut loose from authorized organization and equipment tables and use an improvised unit suitable to the conditions. It is also very important that each transport carry a unit complete in itself for normal reduction operations; there can be no forming of special forces on blue water without great waste of ships, troops and time. (It is not meant that the proposed unit should be a permanent unit in the Marine Corps, as it is believed that the permanent formation of any unit higher than a company is most uneconomical. Company units, numbering among them, in proper proportion, all of the arms and services which will be required in war and temporarily organized into commands for training and economical duty in peace time are considered much the best for many reasons.)
Proposed Landing Regiment:
Total: 2000 Officers and Men.
Headquarters Company (Pioneers; 4 radios) 125 officers and men Supply Company (including boatmen) 125 " Gun Company
( 8 75mm)
" Machine-Gun Company (30 guns) 125 " 3 Battalions riflemen (500 each, minimum) 1500 "
With the foregoing as a basis, it is estimated that the following fighting forces are required for the reduction of the sea objective in question:
(1) Eniwetok 2 Regiments (2) Wotje 2 " (3) Jaluit 1 " (b)
(1) Mille, Etc. 1 Regiment (2) Likieb, Etc. 1 " (3) Elmore, Etc. 1 "
TOTAL: 9 Regiments, 18,000 officers and men.
Technical Advanced Base Force
Floating Force Reserve
1st Brigade: 3 Regiments, Wotje-Mille area; 2d Brigade: 3 Regiments, Eniwetok-Likieb area; 3d Brigade: 2 Regiments, Jaluit-Elmore area.
Force Reserve: Technical Advanced Base Force and one landing regiment.
Characteristics of the Island Anchorages. In view of the recent developments in certain types of sea power, and as a basis for comparison, it will be well at the outset to enumerate the natural military characteristics generally desirable in a modern advanced base. In general terms they may be stated as follows:
The Defense of Fleet Bases
- Anchorage space for main body and train--about 20 square miles with depth of 8 fathoms.
- Smooth water, for the refuge of a large number of light vessels and seaplanes.
- Land and water areas suitable for the operation of land and water planes.
- Defilading anchorage, to prevent view from sea as a primary protection against enemy attacks.
- Shallow, narrow, defiladed entrance, to afford protection against the entry of enemy submarines and torpedoes and facilitate the sudden surprise exit of our own craft.
- Shore line and adjacent terrain suitable to a reasonable separation (aerial bomb and gun salvo distance) and defilading of shipping, aircraft and base facilities--so as to offer the most difficult targets to enemy gun fire and aerial bombing.
- Suitable terrain salient to the harbor entrance--to facilitate wide and distant sea observation and to extend the effectiveness of the fixed defense.
- Deep water approaches to the base--to restrict enemy mining operations as far as possible.
- Sea bottom in the vicinity of the base unsuitable for submarine resting grounds--to make enemy operations as arduous as possible.
- Natural resources in the way of materiel, food and water.
After a consideration of the foregoing, it may be seen that the anchorages in the theatre of operations in question are not very satisfactory from a military point of view.
In the case of the atoll anchorages, the principal disadvantages are as follows:
- They are open to practically all-round view from the sea, being masked from vision only by distance or by island vegetation not over 100-ft. in height, in limited arcs.
- They offer practically no protection from the winds except in limited areas directly under the lee of coconut islands.
- They are salient to the sea. The advantages of a retired harbor can be gained only by a shift of anchorage--seldom practicable without placing ships in the same relative position in another direction.
- Dangers abound, in the way of foul water and strong and uncertain currents.
- The adjacent terrain, by its conformation, renders the masking and defilading of facilities very difficult, and also restricts the command and projection of the fixed defense elements.
- The reef passes are sometimes quite distant from islands, thus making their observation and defense by a fixed defense almost impossible in certain cases.
In the case of the volcanic island anchorages, the principal disadvantage is, of course, that they are too small in area. Being partially formed by reefs, they have also some of the disadvantages (navigation hazards, visibility and saliency to the sea) common to the atoll type, but not to the same degree. On the other hand, the adjacent terrain (mainland and detached islets) favors natural protection for base facilities and fixed defense elements and permits of the latter's projection and of good observation.
None of the anchorages in the theatre of operations afford natural resources to any extent. There will be no reserve food supply, and even a water supply cannot be depended upon in the atoll type. For construction work there will generally be available rough timber of some kind which will answer the purpose, also concrete material. But it must be realized that the timber on the atolls consists of coconut trees and other spongy growths, and the concrete material of coral sand and coral heads, not fit for use in gun plugs or similar constructions as it will disintegrate upon shock.
Harbor facilities, roads and housing facilities will be practically nil, and those that are needed must be constructed by troops upon occupation.
As stated heretofore, it is not probable that the enemy will employ large fleet units in the theatre of operations under consideration. Even his battle cruisers, although particularly adapted for wearing-down operations, will be husbanded for the final fleet action, their preliminary employment being limited to non-hazardous morale demonstrations and possibly the destruction of train vessels and isolated fleet units in blue water. As a matter of fact, the use of these ships will not be necessary to furnish gun support for his operations, as he has a number of old type battleships and cruisers armed with guns up to 12" in calibre which can be used to especial advantage in this case. The numerous close-linked island groups lying in close proximity to any bases which we may have are particularly favorable to the best use of gun vessels of slow speed and small steaming radius as well as to all auxiliary forces. Attacks may be projected and withdrawn swiftly under such conditions--a single night may suffice for a complete operation.
We may therefore look for the following forms of attack against our bases:
- Bombardments by gun vessels of lesser types.
- Torpedo attacks by destroyers, submarines and airplanes.
- Mine attacks by surface vessels and submarines.
- Blocking attacks by small vessels.
- Bombing and automatic-gun attacks by airplanes.
- Raids by landing parties.
Whatever the objectives of such attacks may be: fleet units, train vessels, fuel tanks, hangars, radios, supply, depots, dock facilities, or fixed defense elements, they will always be made with the aim of lessening, directly or indirectly, our power in the ultimate fleet action. The enforcing of undue activity of our fleet units for train protection, scouting, mine sweeping, etc., may produce just as much damage to fleet efficiency as the actual destruction of fleet units.
Before proceeding further it will be well to outline briefly the general characteristics and tactics of the various elements of enemy military strength which will be likely to be employed against us:
Gun Vessels. These vessels, firing up to 18,000 yards, may be used to good advantage in direct or indirect bombardments and in supporting sea or land raids and in blocking attacks. Gun fire in itself is well worth
while where an enemy has been in possession of the scene of action and has had ample time accurately to plot target areas, reference points and firing positions and to arrange with pro-enemy natives (or his own troops which may beat large in the bush) for the setting of range marks or lights. Gun vessels would, ordinarily, carry out bombardments at night, if firing on known territory, and would be supported by submarines.
Mine-Layers. These vessels, other than destroyers and submarines specially equipped, will probably consist in the main of light converted vessels up to 2000 tons, with moderate speed. In addition to these there will be a limited number of regular minelayers of about 350 tons, with 12 knots speed, carrying 120 mines which can be laid in about thirty minutes.
Owing to the fact that water too deep for ordinary mining extends directly up to reefs encircling the islands, enemy mining will be restricted generally to reef bound areas and passages. These areas are very favorable to mining on account of their restricted and more or less tortuous channels, little known, strong tidal currents and the general flow of current eastward (toward us).
The enemy has never bound himself to restrictions in mine warfare, and he will probably use both floating and anchored mines in great numbers. The principal attacks will be by the projecting of floating mines into anchorages on the tidal currents and the direct laying of anchored mines in passages and anchorages. In the latter attacks, a delayed-action mine, similar to the "Monday-Tuesday-Wednesday" mine, will probably be used. All mine operations by regular minelayers will probably be carried out at night.
Destroyers. These vessels will have the following characteristics: Tonnage up to 1300 tons; speed up to 40 knots; guns up to about 5-in. calibre, some with triple barrels; torpedo tubes up to 12 in number; mines, when specially equipped, up to 75.
The conditions being favorable to mining operations, it is probable that a number of the older enemy destroyers will be fitted as mine layers and operated as such. Bombardment by destroyers, unless it be against radio stations, etc., of outlying occupied islands and groups, will be rare, owing to the insufficiency of gun range. Night torpedo attacks against shipping at anchor maybe expected wherever there is a chance of success--this principally by discharging torpedoes through passages or over reefs of the atoll anchorages at those stages of the tide which give sufficient depth of water and range (aid of current).
Submarines. The characteristics of these vessels will be substantially as follows: Tonnage up to 1800; speed, surface, up to 18 knots, submerged, 1Y2 to 10 knots; radius up to 60 hours, submerged; guns up to 6-in.
calibre, with high-angle fire up to 14,000 yards; torpedo tubes up to 8; mine-laying equipment for laying mines while on the surface or submerged, up to 30 mines.
As indicated above, submarine attacks against bases may occur during night or day and will consist of long-range or other attacks as follows:
- Long range (up to 14,000-yds.) bombardments; direct or indirect fire;
- Close attacks with guns and torpedoes (the latter against ships in refuge);
- Mine attacks against anchorages and their approaches.
Submarines being a most dangerous enemy and comparatively little known to Marines, it may be well to consider their peculiar habits somewhat in detail.
Submarines prefer to remain on the surface, for better observation and for fuel economy. When patrolling on the surface by day, they will probably have a little of the upper deck showing and will steam slowly--6 or 8 knots. In this condition they can submerge in from 30 to 40 seconds. If in sight of the coast or near hostile patrols, they will remain submerged, diving about and periodically showing a good length of periscope in order to obtain range of vision. They take every opportunity to recharge batteries and, if on diving patrol or engaged in action during the day, they will come to the surface after dark and recharge, if conditions permit. They keep under weigh while recharging, moving away from probable hostile areas. When attacking, submerged, submarines must show their periscopes for a short time, at intervals, in order to obtain firing data, and must show their periscopes when actually firing. After firing, a large alteration of course is made to get away from the position indicated by the beginning of the torpedo's track. When attacking with gun-fire, submarines may execute a long-range bombardment (direct or indirect) or, when water conditions permit, approach submerged and come to the surface and deliver a close attack. When attacking with mines, they may approach submerged, expose the periscope to verify position, and then dive and lay their mines.
Submarines on the surface are sometimes disguised as other types of vessels. When submerged, their presence may be indicated by an outline of the shape, by the wake or by an oil track. They are very difficult to spot when approaching up a searchlight beam or in the direction of the sun. When attacked, submarines may proceed to the bottom and rest, if the depth of water is not too great (200 feet) and the bottom is reasonably firm and smooth.
In the theatre of operations in question, the submarine will have the advantage of deep water and knowledge of it for an attack approach, but the disadvantages of exceptionally clear water on the approach and of foul ground, shallow water and strong currents on the scene of action. This combination will tend to restrict his operations to the hours of darkness, when he may run a-wash or may use his periscope freely.
Airplanes. The development of airplanes is proceeding so swiftly that their characteristics and method of attack can only be foreseen in a limited degree. However, the following is probable in the case of bombers, the type which is of particular interest to us: speed, up to 100 miles per hour; radius, 7 hours' fuel, about 200 miles from base; personnel, about 5 men; bombs, up to 2000-lbs, in charges suitable to targets; guns, up to 6 machine-guns of largest calibre with arc of fire of 360° except for small dead angles.
In addition to bombers, planes will probably be developed for launching torpedoes in the water against ships and for carrying large automatic or quick-fire guns for employment against ships, shore facilities and the land forces, with the object of firing materiel or strafing personnel. Attacks by dirigibles will also be possible, but their strength will probably not exceed that of the bombers.
Bombers normally attack up and down the wind. They may attack during the day or on moonlit or starlit nights. The normal altitude for day attacks is about 15,000-ft., for night attacks from 5000 to 6000 feet. At night the machines attack singly, departing from their base at several minute intervals. During the day they generally proceed in formation, 7 to 9 machines. Bombers prefer line targets, so that they may plane over them lengthwise. Having an all-round defense, bombers may proceed to the attack, especially at night, unattended by other types of aircraft.
Attacks with machine guns may be made by any type of airplane against materiel and personnel (using incendiary bullets on the former) during the course of any air attack, it being merely a question of the appearance of a suitable target, combined with a good opportunity.
While the weather conditions are none too good and the terrain is generally thick, the theatre of operations in question greatly favors enemy air operations, in that the numerous islands and reefs, if known, form good navigational marks, the size and shape of atoll islets enforce restricted land targets for airplanes, and the terrain being practically virgin, the fact of occupation or work at any point will be fairly easy to spot.
Blocking Vessels. These may be any old type suitable for closing reef passages. The vessels to be sunk will be escorted by auxiliary craft of all types and possibly accompanied by a land raiding-party for effecting shore demolitions. These attacks, being close attacks, would ordinarily be effected at night, or at least in thick weather or under smoke. The anchorages under consideration lend themselves in many cases to blocking attacks by reason of their narrow, tortuous and comparatively shallow passages; but this advantage is partially offset by the uncertain and strong tidal currents which flow through them and their general obscurity under bad visibility, thus making the approach and placing of block ships difficult.
Land Raiding Parties. These parties, of comparatively small strength, will consist of foot troops with explosives whose object will be to destroy important base facilities or elements of the fixed defense at our bases, or possibly radio plants, etc., on islands which are simply occupied by our mobile troops. The development of demolition explosives, both in form and power, enables an enemy to carry out these operations with great speed.
Land raids will nearly always be possible only at night, and will probably be carried out in conjunction with other forms of attack.
The deep passages into volcanic island anchorages render land raids by these routes very difficult, and a landing on the open coast would necessitate a comparatively long march on shore to the objective. In the case of atoll anchorages, facilities will also, in most cases, be a considerable distance from the reef passages, which would make a land raid difficult; the facilities would, however, always [be] closely adjacent to the open sea and thus favor land raids, providing sea conditions permit of a landing on that side.
[B L A N K P A G E]
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