Value and Tactics of the Modern Submarine.
The military value of any vessel designed for war purposes depends largely on the following factors:
- Communication, or the ability to transmit and receive information or battle orders either before or during contact with an enemy.
- Mobility, or the ability to move quickly from place to place in all conditions of weather. Under this factor may be included the habitability of the vessel, or its ability to maintain a crew in normal health and fighting power.
- Invulnerability, or the ability to resist attack.
- Offensive strength, or the ability to deal a telling blow when in contact with the enemy.
In estimating the military value of the submarine or submersible, as compared with the modern battleship, we find that each has a distinct and separate value. The battleship on account of its mobility as defined above can operate where submarines or submersibles of the present day cannot go, due to their lack of mobility. On the other hand, leaving out the factor of mobility, which for submarine craft of the future will advance more rapidly than for surface craft, we find that submarine craft rank equally well, if not better than surface craft.
Submarine craft on the surface within sight of each other have the same ability as other surface craft to communicate freely, using for this purpose the various systems of day and night signalling used in surface craft. For long distance signalling the submarine or submersible has a radio outfit capable of operating at distances up to fifty (50) miles. As the range of the radio outfit depends on the height of the aerial, the larger submarine boats can easily obtain a greater range by using higher masts. The present practice consists in carrying the portable aerial on two masts which fold down on the deck just before submerging. The sending and receiving apparatus is permanently installed in the forward end of the submarine, as far as possible from the noise and vibration of the propelling machinery. Sketch "A."
The sketch shows the arrangement of the masts and aerial as rigged on submarines in our service. In this rig the aerial is about thirty (30) feet above the deck, and can be taken down ready for submergence in five (5) minutes. The value of the radio outfit in time of war is greatly increased by the proper use of fast scouting vessels also equipped with radio.
For communicating below the surface, submarine craft use bell signals, the bell being sounded by a pneumatically operated striker from inside the boat. Under the most favorable circumstances, with all machinery stopped, boats have exchanged signals at distances up to eight (8) miles. Under the most unfavorable conditions, with boats running away from each other on opposite courses, signals have been exchanged at distances up to one-half of one mile. Numerous experiments have been made to establish reliable radio communication below the surface, but, up to the present, without success.
As submarine craft on "station" or prior to sighting an enemy's smoke will habitually remain on the surface, and as submerged communication by means of a bell or sounding apparatus can be intercepted by friend or foe alike, there is no practical value to this method of communication, except to avoid collision in training exercises in time of peace. A group of submarines operating submerged and using bell signals in the presence of an enemy can easily be located along certain lines of bearing. If then, the enemy is equipped with receiving apparatus as most modern ships are, he has only to run away to avoid torpedo attack. The submerged speed of a submarine or submersible will never equal or exceed the surface speed of a battleship unless that battleship is disabled, therefore a submarine commanding officer should be very loath to sound his bell for safety's sake, and thus lose the chance of coming within torpedo range.
The development of the Diesel internal combustion engine has added greatly to the mobility and safety of the submarine. Among the many advantages of the Diesel engine over the gasoline engine are the following:
- Economy in cost and consumption of fuel.
- Increased cruising radius for a given tank capacity.
- Increased reliability of performance.
- Greater safety in handling of fuel.
- Absence in engine room of noxious fumes and gases.
The fuel consumption per horse-power hour varies slightly with the size and speed of the engine, being lowest for large and slow speed engines, and a little higher for small and high speed engines. A fair average fuel consumption is .5 lbs. per brake horse-power per hour. The average specific gravity of ordinary fuel oil is .89, equivalent to 7.4 lbs. per gallon. The fuel consumption therefore amounts to .54 of a pint per horse-power hour. The average price of such oil is 3 cents per gallon, making an average fuel cost of .2 cents per brake horse-power. In a gasoline engine of about the same power, the average consumption is one pint per horse-power hour. With gasoline at an average cost of 12 cents per gallon, the cost of the gasoline engine is 1.5 cents per brake horse-power hour, or about 7^ times the cost of the fuel oil engine.
The use of the internal combustion fuel oil engine has practically doubled the cruising radius of submarines and has made it possible for these craft to have about the same cruising radius as a modern battleship. The surface speed of the submarine is naturally not as high as that of a battleship, due to the spindle form of hull of the former, that being a poor form for surface speed, but an excellent form for submerged speed and strength. In order then to attain the surface speed necessary to permit a group of submarines to cruise with a battle fleet, it will be necessary to adopt a "ship shape" form of hull, and thus sacrifice a small amount of submerged speed and strength. Whereas contractors guarantee a strength capable of withstanding a pressure at 200 feet in a submarine of the spindle form, they will only guarantee 150 feet submergence, with safety, with the "shipshape" form of hull.
The total absence of an ignition system and all of its attendant troubles tends to greater reliability of motive power. With the two-cycle reversible type of heavy oil engine, the number of moving parts is reduced to a minimum, and the engine is very compact and easily accessible for overhauling.
The use of heavy oil instead of gasoline in submarine craft has removed the greatest source of danger. The only accidents worthy of mention in our service have been due to gasoline fires in the torpedo compartment, or in the engine room. The moral effect on the crew caused by the removal of the gasoline danger cannot be overestimated.
In the use of gasoline engines, there is always an odor of raw gasoline or of burned gasoline in the engine room. In fine smooth weather, it has been possible to keep the engine room fairly well ventilated, but in rough weather the hatches must be battened down, thus making it very difficult to rid the boat of fumes. Numerous cases of "gasoline jags" have occurred both at sea and in port. The victim on watch in the engine room inhales the raw gasoline fumes which come from the engines or from the fuel pumps, which are very difficult to keep tightly packed. He gradually loses his senses, and just before lapsing into total unconsciousness, becomes very violent. If he is not immediately removed from the engine room he may fall into the moving machinery. The aid of several men is sometimes necessary to control the struggles of the "jag," and thus prevent self-injury before he loses consciousness. The after-effects of such a case is usually a violent nausea and headache, and an extreme distrust of the gasoline engine. The use of heavy oil fuel has removed the source of danger from submarines and has made it possible to keep the engine room air good and clean in all conditions of weather.
Before leaving the question of mobility, it will be well to point out that submarines and submersibles have about the same qualities as surface craft as regards handling under various conditions, and as regards towing. Submarines may be towed with their crews aboard at speeds up to twelve (12) knots, the reliability of the operation depending only on the reliability of the towing apparatus. They may be submerged with absolute safety in all conditions of weather. In heavy weather they may be sealed up, that is, all hatches battened down, and navigated with absolute safety from the conning tower. Under such conditions, the air necessary for the engines and the crew is drawn into the boat through a ventilator controlled from inside the boat.
In comparing the invulnerability of the submarine with that of the battleship, we find that where the battleship has armor whose resisting qualities are always more or less doubtful, the submarine has complete invisibility until within torpedo range, and after 'arrival within range has only two very small periscopes momentarily exposed over a hull about twelve (12) feet under the surface. The difficulties of hitting such a small moving target are great, and it must be kept in mind that the submarine at this stage of the action has already fired her torpedoes and inflicted her damage. There is no accurate information at hand to show the effect of firing a large shell at a hull submerged about ten (10) or twelve (12) feet, but recent experiments in England show that a submarine anchored with the hull about ten (10) feet below the surface can be sunk by heavy gun fire at comparatively short ranges.
The offensive strength of a submarine lies in her ability to maneuver submerged to within easy range of a surface vessel, and then to fire torpedoes without being subjected to a dangerous fire from her enemy. The surface vessel has no defense against the submarine, except her speed in running away, and in doing this she may be running directly into the danger zone of another group of attacking submarines.
The steady development of the torpedo together with the gradual improvement in the size, motive power, and speed of submarine craft of the near future will result in a most dangerous offensive weapon, and one which will have a large part in deciding fleet actions. Even at this present day it is impossible for an enemy to blockade a port protected by submarines, and decidedly dangerous to even attempt operations anywhere along the coast where it is known that submarines are employed in the coast defense.
Submarines and Submersibles.
The hull of the submarine is generally of the spindle form, the cross sections being circles. This form of hull gives greater strength for equal weight of scantling, and is the form best adapted for submerged speed. With this form of hull, however, the maximum surface speed is reached when running at about fifteen (15) knots. The reserve buoyancy of the submarine when light is about twenty (20) per cent of the total displacement. The submersible has a "ship-shaped" form of hull, that is, its hull has more nearly the form of a surface torpedo boat. The surface speed of the submersible can easily be made high enough to enable it to accompany a sea-keeping fleet of battleships, whereas its submerged speed will fall about twenty (20) per cent below a submarine of equal size. The submersible having a reserve buoyancy of about sixty (60) per cent is apparently a better sea boat than the submarine. The submersible with its "ship shape" hull cannot be built with the same strength as the submarine, and where submarines are built to stand a submergence of two hundred (200) feet with safety, the submersible is guaranteed only to depths of one hundred and fifty (150) feet. It would seem then in order to obtain groups of sea-keeping submarine craft, it will be necessary to adopt the "submersible" type.
The relative advantages and disadvantages of the two types are given as follows:
(a) Greater submerged speed and strength.
(b) More torpedo tubes in bow due to blunt form.
(c) Less habitability due to reduced buoyancy and sea-keeping qualities.
(d) Lower surface speed due to poor form of hull.
(e) Greater surface speed.
(f) Greater habitability and sea-keeping qualities.
(g) Reduced strength and submerged speed.
(h) Fewer torpedo tubes in the bow due to fineness of form.
As regards control on surface and submerged, the two types are practically the same. The submerged radius of action of the submersible is slightly less than that of the submarine, while its radius of action on the surface is slightly greater.
Modern Types of Submarines and Submersibles.
The accompanying plate, Figs. 2 to 8, taken from Engineering, by permission, shows a modern submarine of the following approximate dimensions:
Length 150 feet.
Beam 15 ft. 6 in.
Displacement (surface) 390 tons.
Displacement (submerged) 520 tons.
Buoyancy percentage of submerged displacement 25 per cent.
Buoyancy percentage of surface displacement 33 per cent.
Surface speed 14 ½ knots.
Surface cruising radius 4500 nautical miles.
Submerged speed 10 ½ knots.
Submerged radius 120 nautical miles.
Safe depth of submergence 200 feet.
Armament 4 torpedo tubes and 8 torpedoes.
Figs. 9 to 14 on the accompanying plate show a modern submersible of the following approximate dimensions:
Length 212 feet.
Beam 21 feet.
Surface draft 12 feet.
Surface displacement 650 tons.
Submerged displacement 950 tons.
Buoyancy percentage of submerged displacement 31 ½ per cent
Buoyancy percentage of surface displacement 46 per cent.
Armament 8 torpedo tubes.
Surface speed 17 knots.
Submerged speed 11 knots.
Surface radius of action 5000 nautical miles.
Submerged radius of action 140 nautical miles.
Safe depth of submergence 150 feet.
The submersible herewith is similar in many details to those built in France from the designs of M. Laubeuf, and in Italy from the designs of Major Laurenti.
Tactics of Submarine Craft.
Definitions are here given to the terms "light" condition, "awash " condition, and "submerged" condition.
A submarine in the "light" condition has all of its water ballast tanks empty, and has its cruising bridge rigged. With the present form of cruising bridges, it is estimated that at least twenty minutes will be required to trim down to the submerged condition. In the new boats, however, folding bridges are under consideration which will require much less time to strike down.
A submarine in the "awash" condition has only those water ballast tanks empty which are habitually kept full when running submerged. The fore and aft trimming tanks and two smaller tanks, called the auxiliary and adjusting tanks, are filled with just enough ballast so that when the main ballast tanks are filled, the boat will be immediately ready for running submerged without further adjustment of ballast. The quantity of water in the trimming tanks and in the auxiliary and adjusting tanks, in the "awash" condition, is so small in comparison with the total ballast, that for all practicable purposes the submarine has the same stability and safety as when running "light." In the "awash" condition a small section of bridge may be kept up for the lookout, and the conning tower hatch may be kept open and the radio rigged. It is estimated that five minutes will be required to trim down to the "submerged" condition from the "awash" condition. If any fuel is used while in the "awash" condition, the additional necessary weight can easily be computed and added to the trimming tanks. In time of war all submarines on station should habitually remain in the "awash" condition.
A submarine in the "submerged" condition has its ballast tanks and other tanks so filled that there still remains a small reserve of buoyancy (0 to 800 lbs.) and is all ready to run submerged.
For the purpose of tactics submarines may be divided according to their capabilities into three classes, viz., harbor defense, coast defense, and sea-keeping offensive submarines.
Taking into consideration the capabilities of the harbor defense boats, this class should be sent to the Philippines, where the areas of defense around such strategical points as the entrance to Manila or Subig bays are comparatively small. Four of this class are now in commission in Manila Bay, two are in commission on the West Coast, and four are in reserve in Charleston, S. C. The five new boats of this class are admirably adapted for the defense of either end of the Panama Canal. For the protection of the harbors on the East and West coasts of the United States, there should be a group of five submarines and one suitable tender stationed at each of the harbors and places which are considered worthy of protection for strategical reasons. There are now only 'twenty-four submarines available for this purpose, and it is estimated that for the proper protection for the East and West coasts of the United States, there should be a total of fifty-five submarines on the East Coast, and a total of forty-five submarines on the West Coast. These submarines should be based on mobile tenders located as follows, one group of five boats operating from each base:
Bar Harbor, Me.
Portsmouth, N. H.
Point Judith Breakwater.
New York, N. Y.
Charleston, S. C.
Key West, Fla.
Port Townsend, Wash., two groups.
Columbia River, Ore., two groups.
San Francisco, Cal., two groups.
Santa Barbara, Cal., one group.
San Pedro, Cal., one group.
San Diego, Cal., one group.
As stated before, there are now twenty-four (24) submarines built or building, and a total of one hundred (100) are required to form a complete chain of defense about the great harbors and cities of our country. No mention has been made of the submarines for the defense of our over-sea possessions, such as Guam, Hawaiian Islands, etc., but it is believed that a mobile tender with a group of five (5) submarines will most effectually prevent the operations of a hostile fleet in these waters.
The tactics of a group of harbor defense submarines are extremely simple. Their limited submerged radius and speed will not enable them to operate far from the entrance of the harbor which they are protecting. The lack of reliable under-water communication makes it impossible to change plans of action once the group is submerged, without giving the enemy a clue as to the submarine's whereabouts. The argument might here be made that the enemy must know that certain harbors have submarines for their protection, and that a prudent enemy would not venture to attack such a place, and that the submarines would thus accomplish their object without further effort. That might be true enough, but there are always enough commanders of the "damn the torpedoes and submarines" type who would take the risk, and it is for such kind that arrangements must be made. Any form of under-water signalling device at use in the present time can be accurately located in direction by the enemy. This apparatus for locating the direction of submarine signals is installed on practically every modern ship. So, for this reason alone, must the detailed plans for a group of harbor defense submarines be made explicit enough to cover every phase of an attack by a determined enemy.
Each boat of a group must be assigned a certain area outside of the harbor, which will be its zone of defense, these zones to be so selected that all approaches to the harbor are protected, and to be at such a distance from the point of defense that the enemy will never come within gun range. Most of our harbors lend themselves naturally to such a method of defense by the form of the channels leading to them, or by the presence of islands in the vicinity. A harbor defense group, having received warning from scouts or shore stations, of the movements of the enemy off the coast, immediately proceeds to the entrance, leaving the tenders inside the harbors. Submarines anchor in the "awash" condition, radio up, in the centers of their zones and keep a lookout for the enemy. By sub-dividing the total area outside each harbor into numerous small squares and using short code words to designate squares and directions, our scouts in touch with the enemy can easily keep the waiting group of submarines informed as to the enemy's movements. This method was successfully used last summer in the combined maneuvers off Block Island, and had the waiting submarines been equipped with radio, the results would have been even better than they were. As it happened last year, the submarines were dependent upon a fast scout to come from an inner scouting line and give information by signal or megaphone to the submarines in their zones. The waiting submarines having ascertained definitely, or in all probability that the enemy will pass close to their harbor, immediately get up their anchors, lay down their radio masts and submerge as soon as smoke appears on the horizon. With a moderate amount of their periscopes exposed a submarine can easily see a large ship in clear weather for a distance of seven or eight miles. During maneuvers in Long Island Sound with the U. S. S. Dixie, her masts and smoke were easily seen from the Snapper's (C-5) periscopes at a distance of nine miles, with about four feet of periscopes exposed. The submerged group, each boat in its zone, remain stationary until the movements of the hostile fleet are definitely ascertained. By the arrangement of the zones, the enemy must pass close to one submarine; the other boats must then move over towards the enemy at such speeds and with just enough periscope exposure to enable them to get within torpedo range without detection. Once within torpedo range they keep their periscopes exposed and make all speed possible to get within easy torpedo range to fire their torpedoes at that part of the enemy's formation previously assigned to them. In this last maneuver they must act regardless of their other boats, and must take the risk of collision. On this final charge, the submarine bells may be rung continuously to assist the submarines to keep clear of each other. Having fired their torpedoes, the boats submerge totally, and reload their tubes if they have spare torpedoes. During the period of reloading they may run at such depths as would enable them to pass under the enemy's vessel, or if the depth of water permits, they can rest on the bottom until the reload is finished, when they should return to the surface to inflict such further attack as is possible. A submarine having exhausted her supply of torpedoes has still a most formidable weapon in her ram. That this weapon is most efficacious and without danger to the crew of the boat was proven in the fall of 1910, when the C-4, at a comparatively low submerged speed rammed the tender Castine, causing her to settle immediately. There can be no doubt that the torpedo properly adjusted, and used with the short ranges possible in harbor defense, will be effective. There are even instances on record where torpedoes with exercise heads have seriously damaged the hulls of vessels by the force of impact.
The harbor defense group having exhausted its means of offense should return to the tender, submerged, if necessary, or under cover of darkness, to replenish torpedoes and storage batteries.
For the night defense of the harbor, submarines remain on the surface in their zones, being used in this manner most effectively as surface torpedo boats. The tactics on the surface as torpedo boats are similar to the tactics employed in surface torpedo craft, and as they are well known to the service, they need not be described here.
Coast Defense Submarines.
The distinction between a coast defense and a harbor defense submarine lies in the greater submerged and surface endurance, the greater submerged and surface speed, and the better habitability conditions of the coast defense boat. Considering the most inferior of our present coast defense submarines, we find that they have been making cruises up and down the coast as far south as Norfolk, Va., and as far north as Gloucester, Mass.
Our government on account of the general topography of its coast should not build any more strictly "harbor defense" boats. A "coast defense" group will accomplish with greater effect the same duties that' are now accomplished by the harbor defense group. Countries in Europe are so close together that smaller submarine craft and more of them are of greater military value than fewer and larger submarines. Our general policy of submarine construction should not be too greatly influenced by the building programs of European nations. Ours is a separate and distinct problem.
In considering the tactics of a group of "coast defense" boats, it is assumed that information has been received from reliable sources, scouts or shore stations, that the enemy's fleet is approaching our coast with the evident intention of seizing a base or of landing a force. The group proceeds at its highest reliable surface speed in column in the "awash" condition, with radio up, to intercept or to come in contact with the enemy. The submarine with its low hull can easily distinguish the masts and other characteristics of a vessel when the submarine cannot be seen at all. On sighting the smoke or masts of the hostile fleet, and having approximately determined his course, the entire group immediately submerges, after rigging down the radio, and proceeds submerged at about one-half mile distances in the general direction of the enemy at such speeds and under such general directions as may have been previously issued by the group commander. The submarine group, submerged at one-half mile distances can easily keep clear of each other. They must then maneuver to keep a position on either bow of the enemy's column in order to insure their getting within torpedo range before being sighted. This approach must be made totally submerged, with an occasional "porpoise" or periscope exposure of short duration. When within torpedo range periscopes should be exposed enough to keep an easy bearing on the enemy, and the speed increased as much as possible to arrive within "easy " torpedo range (between 500 and 1000 yards) before the enemy has time for a concerted maneuver. Each submarine fires its torpedoes at the parts of the formation previously agreed upon, totally submerges, reloads as soon as possible, and returns to the attack. The following sketch to scale shows the most favorable condition under which a group of submarines in contact with the enemy can fire their torpedoes. Using torpedoes, capable of angle fire, a four-tube boat should set one torpedo to run five degrees to port of her keel, two to run straight ahead, and one to run five degrees to starboard of her keel.
The movements of each individual boat in contact with the enemy will be dependent on the enemy's formation. Tables showing the proper bearings on which to fire torpedoes with maximum chances of hits, have been compiled for every formation and are readily understood by submarine officers. It is not expected that every shot will be a hit, nor that every ship of the enemy's force will be disabled. It is hoped that, however, with the above method of firing enough damage will result from the discharge of 20 torpedoes to prevent the enemy from accomplishing his purpose. Attention is also invited to the fact that with accurate knowledge of the enemy's whereabouts off the coast, two or more groups may be despatched to the probable destination of the enemy to deliver an attack as shown above. Under such a condition the other group should attack other parts of the formation. Submarine groups, having exhausted every means of offense, including the torpedoes and ram, should withdraw submerged at low speed or lie on the bottom, if that is possible, until nightfall and then return to the base of supplies under cover of darkness, charging their storage batteries on their way into the base. All attacks so far have been assumed at a moving enemy. Should the attacking group discover the enemy at anchor, landing troops or establishing a base, they should continue as above outlined, totally submerged with only an occasional "porpoise" of short duration until well within torpedo range, when the periscope should be kept submerged until the torpedoes are fired at easy ranges at prearranged parts of the enemy's formation. No special difficulty is anticipated in passing the line of enemy's scouts or pickets with the submarines running totally submerged with occasional "porpoises."
It must be understood that after the reload of torpedoes, the submarines must act absolutely independently, and that it is impossible with the present lack of underwater signal facilities to communicate. In all cases the chief duty and aim of the group commander must be to bring all of his group into contact with the enemy and within torpedo range at the same time. Having done this, it is up to the individual commanding officers to produce the desired results.
Tactics of an Offensive Sea-Keeping Group of Submarines.
It is not within the province of this discussion to determine the exact tonnage and horse-power of a "sea-keeping" submarine. That information can only be obtained by actual experience in running a group of submarines with a fleet engaged in active war maneuvers. No amount of computation of the number of cubic feet of space necessary for each person on board will suffice. A "sea-keeping offensive" submarine may be denned as a submarine which can keep the sea, ready for duty under all possible conditions of weather for indefinite periods. Such a submarine group could obtain its supplies from vessels of the fleet which it accompanies, and be in every respect as mobile as any unit of the fleet.
The tactics of such a submarine group after contact with the enemy will be the same as the tactics already described for harbor defense and coast defense submarines in contact with the enemy. The problem of maneuvering such a group into contact with the enemy, or to more accurately state the case, the problem of maneuvering the enemy's fleet into the "submarine danger area" must be solved by the commander-in-chief.
As an illustration of the use of one or more offensive submarine groups accompanying a fleet, let it be assumed that the submarines have a surface speed capable of cruising with the fleet at any speed that may be required to keep up with the fleet. Let it be also assumed that the submerged speed and the radius of the submarines is about twelve knots for one hour, or about eight and one-half knots for four hours, or about five knots for fifteen hours. These assumptions are not excessive. Suppose also that in the cruising formation submarine groups take position on either flank of the fleet. The submarine groups are in the "awash" condition ready for instant use. The commander-in-chief having received information from his scouts of the presence of the enemy, or having sighted the enemy, should immediately send his submarine groups "awash" off on a bearing previously decided upon, and then endeavor to maneuver his opponent into the area occupied by the submarines. The 'submarines may remain "awash" until the enemy's smoke or masts are sighted. If our commander-in-chief possesses a superior speed he can choose his own situation, and having patience can eventually bring the enemy into the submarine area. If our commander-in-chief possesses the inferior speed he may be forced into action before bringing the enemy into the submarine area. In this case submarine groups should maneuver "awash" or "submerged," as is necessary to keep out of the enemy's sight and endeavor to attack the enemy's formation as soon as possible without interfering with the movements of the commander-in-chief. If our commander-in-chief has the inferior speed and inferior force, and if the enemy is determined to bring about an action, the problem of making him cross a submarine danger zone is greatly simplified. The appearance of several groups of submarines within or very close to his formation just before a general gun action would undoubtedly cause the enemy to so alter his plans and formation that he would be at a temporary disadvantage, and at the mercy of our fleet. Even if all the torpedo shots missed, the effect on the morale of the enemy would be sufficient to give our commander-in-chief a temporary advantage. Most of the important fleet actions have been fought in sight of land or close enough to shoals to cause the movements of the vessels in action to be somewhat restricted as to courses. In cases of this character the commander-in-chief can so station his submarine groups as to increase the chances of forcing the enemy into the submarine danger area. The commander-in-chief must make a careful study of the areas in which fleet actions may be anticipated in order to utilize to their maximum value the capabilities of the submarines in his fleet. If the commander-in-chief desires to withhold the submarine attack until after the gun fire, the submarine group should be kept in the background within easy radio signal distance, but in doing this, the commander-in-chief must realize that it will be more difficult for the submarine groups to make a successful dash across the space between the engaged fleets, due to the inferior submerged speed of the submarines. Ships of the enemy that are already disabled would in such cases become easy prey for the submarines. Submarine groups accompanying a fleet are decidedly offensive weapons and of the greatest value when used just preceding a general gun action.
A ruse which might assist in forcing the enemy to keep away from certain areas and thus increase the chances of making the enemy cross the submarine danger zone would consist of having the fast scouts of the fleet drop numerous poles, properly weighted, to float upright in the water, and painted to look like a submarine's periscope. These same dummy periscopes floated out of a harbor with an ebb tide or dropped outside by scouts or fishermen may greatly influence the movements of an enemy sighting them. It would be extremely difficult to distinguish between dummy and real periscopes, for it is easy for a submarine to lie submerged and stationary with only a small amount of periscope showing.
The night maneuvers of submarine craft are the same as for surface torpedo craft, and the same tactics should apply. As there is no possibility of "torching," and as the hull is so low in the water, it is extremely difficult to pick them up at night, even in the full rays of the searchlight. The maneuvers off Provincetown in the summer of 1911 demonstrated that in nearly every case the submarines could come within easy torpedo range of the enemy at night without detection. In a night attack submarines should remain in the "awash" condition, so that in case of self-preservation, or to pass through a picket line, the submarine can quickly run submerged.
At night submarines on the surface will use the same recognition signals used by all surface vessels of the fleet. During daylight operations the problem of recognition is much more difficult. At comparatively short ranges, 3000 yards and less, the submarines submerged can recognize a friendly vessel by her silhouette, or at shorter ranges by certain flag or shape signals shown from specific parts of the surface vessel. If surface vessels are fitted with submarine signal apparatus, code recognition signals may be sent, using the bell within the limited distances mentioned in this discussion. By properly screening a submarine bell it is quite possible to send the sound waves out on a line of bearing, or at least within a very small arc. However, in the absence of the submarine bell the battleships or surface vessels must rely on their flag or shape signals to make themselves known as friends. The submarine has only two methods of recognition signals at her disposal, one, sounding code words or letters on her bell, and the other, carrying a certain shaped flag or pennant on her periscope. It would seem that the submarine bell methods would be more efficient at greater distances than the other method, but it has the disadvantage of warning friend and foe alike of the presence of submarines. From a submarine officer's point of view it would seem far better to trust to the judgment of the commanding officer of the submarine to recognize friendly vessels, which he could most certainly do from a silhouette diagram at comparatively long ranges. After recognizing a friend a submarine may rise to the surface and exhibit surface recognition signals, if such are necessary. This method, however, might endanger the submarine before she is recognized as a friend. The submarine officer desirous of getting within easy torpedo range would be very loath to disclose his bearing to a probable enemy by sounding his bell.
A logical and fairly accurate answer to all points under discussion can only be found by continuous combined battle maneuvers, using all the necessary units of a fleet.