(Translated from the Spanish)
*The illustrations are by Alejandro Gavrilof.
Can the falcon be friends with the pike (the fish)? In fairy stories, yes; in real life, no, of course, because their respective interests lie in different elements. Can the airplane serve the submarine as a useful complement and constitute an equipment for co-ordinating its actions? At first sight it seems that that likewise is impossible, but both, created by man for his own purposes, must have interests in one and the same plane, and those interests, precisely, may coincide at the surface of the sea.
The submarine, upon submerging to a great depth, turns completely blind; when it is sailing on the surface or using a periscope when submerged for combat, it is found to be relatively shortsighted, inasmuch as the height from which the horizon is viewed from it is much less than on surface vessels. With the speeds attained today by warships—especially cruisers, torpedo boats, and motor launches, which are at the present time the most dangerous of the submarine’s enemies—it is a matter of the highest importance to the latter, not only to discover them as soon as posable, but to avoid, as far as possible, any encounter with them.
The airplane, flying at a great altitude, embraces a very wide horizon in its observation. Thanks to its small size, it is always capable of discovering a vessel which is passing at a distance long before the latter can discover it. Once discovered and followed by the vessel, it always has the possibility of leading the enemy away in the direction most suitable for it and, thanks to its speed, escaping from his vision whenever it so desires.
Analyzing the marked peculiarities of the submarine and the airplane—absolutely opposite in their nature—we must arrive at the conclusion that, at bottom, they constitute a happy complement to each other and in many cases may render mutual assistance and co-operate efficiently.
After the World War, in the naval circles of many countries, this idea began to take shape in more or less definite forms, inducing the specialists to work out plans for co-operation between the air forces and the submarines, and to make trials of installing airplanes on the submarines in order to render special services to the latter.
Offering many instructive examples, the history of the World War wrote into its pages, among other things, some very interesting adventures of a ship of low speed converted by the Germans into a privateer, and on which the idea of equipping a ship with an airplane was carried out for the first time in just the way that in the future will prove to be the most efficient and useful for submarines.
To give a clear idea of how useful an airplane may be in such cases, we take the liberty, before continuing the study in which we are interested, to relate the said adventures briefly to the reader.
The Wolf, an old merchant steamer of 5,000 tons displacement and a speed of 11 knots, left Germany toward the end of 1916, in the character of a privateer, to sail the Seven Seas and prey upon the enemy’s commerce. To meet any contingency, it was armed with 6 guns and 4 torpedo tubes, but its essential load consisted of 500 mines which were to be sunk in the principal trade routes of international maritime commerce. The Wolf rounded England to the north and headed south through the Atlantic, stopping and sinking enemy merchant vessels. Rounding the Cape of Good Hope, it turned its prow northward and, in the first part of January, laid the first field of mines near Aden. Continuing, it begins a systematic laying of mines at the entrances to the principal ports of India; then the privateer goes to Australia, first to the roadstead of Melbourne; then, leaving Bass Strait obstructed with mines behind her, she appears before Sydney. At Sydney, distant many thousands of miles from the theater of war, no one, of course, was expecting the appearance of the enemy, and for that reason a great tumult was raised when, in an entirely unexpected form, an airplane bearing the insignia of the Iron Cross appeared over the city. Flying very low, the airplane scattered handbills bearing the greetings of the German commanding officer to the people of the city and, without doing any damage, disappeared in the direction of the sea. The Wolf, without being molested by anyone, immediately undertakes a long voyage to the Samoan and Fiji Islands, sailing along New Guinea, and enters the Strait of Malacca, through which passes all the sea trade between Indo-China, China, Japan, and Europe. After laying mines in the parts of the strait most frequented by ships, it passes under cover of night through the roadstead of Singapore and heads for Calcutta, at the entrance to which it again lays mines. It continues its course in the Indian, Pacific, and then the Atlantic Oceans, sinking more than 200,000 tons of merchant shipping, fitting out various auxiliary cruisers, and, after a cruise of 14 months, tranquilly returns to Germany.
The most noteworthy thing about all these adventures is that during its entire voyage, the Wolf did not once encounter an enemy warship, although they were carefully searching for it everywhere. In spite of its low rate of speed, it found it possible to capture a large number of enemy merchant vessels, thus providing itself with coal, provisions, and everything needful. This brilliant success the privateer owed exclusively to its airplane, which was taken aboard by the commander at the moment of leaving Germany. Every day, the said airplane made a distant exploring trip, communicating to its vessel the news of all the ships sighted within a radius of a hundred miles. Its boldness was carried so far that once it succeeded in capturing an enemy ship alone, threatening it with bombs and forcing it to take a fixed course. That airplane was the guardian angel of its master and discharged its duty brilliantly during the whole of the long voyage.
Much attention was given, toward the end of the war, to the important role of airplanes as applied to maritime navigation, and, at the present time, most of the cruisers of nearly every fleet have them as elements of their equipment. The example of the Wolf with its airplane proved to be very instructive for submersible ships, offering them the possibility of acquiring the qualities which they organically lacked. Accordingly it is not surprising that immediately after the termination of the war, in many countries, more or less serious attempts were made to solve the problem at issue.
In France the submersible cruiser Surcouf was equipped with an airplane. In the United States, at first, they tried to install hydroplanes directly on the deck of the submarines, but naturally the results obtained were not very happy. Afterward, on some North American submarines, steel cylinders were installed to protect, during the progress under water, the hydroplanes placed in them which folded in a special manner. In England, there was chosen for the installation of an airplane the submarine M-2, which during the war was armed with a heavy cannon, and took part in military actions. After the war the Admiralty decided to remove the cannon and place a hangar with an airplane aboard the said submarine, and this plan was put in practice. This installation proved to be fatal for the submarine. Toward the last of January, 1932, while navigating not far from the coast of the English Channel, the submarine M-2 sank under mysterious circumstances, with all its crew, and there is no doubt that the cause of the sinking was the installation of the airplane on it, or more properly, the defects of such installation, which is not to be wondered at, as first attempts in any undertaking often result fatally. The tragic disappearance of the submarine M-2 shows clearly that the installation of airplanes on this type of boat does not prove to be as easy as on surface vessels, as it offers a whole series of complications, determined by the conditions peculiar to submarine navigation, which demand a painstaking study in order to avoid causing further catastrophes.
The reader will be interested, naturally, in knowing in what forms such installations can be realized, as well as the conditions which must be fulfilled in order to assure their proper functioning.
Modern airplanes are, in general, such delicate apparatus that it is desirable to preserve them from the action of the water during submersion. This creates the necessity for the hangar in which the airplane is kept on board the submarine being full of air at all times. In the act of submerging, the outer walls of the submarine experience a pressure from the surrounding water which is proportional to the depth at which it is submerged, and when the latter is considerable, it may reach a very high value. On this account, in planning the hangars for submarines, the first thing that must be borne in mind is the a option of measures tending to make them capable of resisting the pressure of the surrounding water. This result is secured in various ways. In the first place, a hangar may be constructed having the same resistance as the hull of the submarine, that is, capable of supporting the pressure of the exterior water up to the maximum submersion admissible. In such a case the shape of the hangar must be cylindrical (Fig. 1), with a hemispherical door that closes hermetically. The advantages of such a hangar consist in the fact that it amounts to a constant float
which requires no special care. In navigation under water, access to the hangar from the interior of the submarine always proves impossible, independently of the depth of submersion. The defect of this type of hangar is its relatively great weight and the fact that it is placed on top of the upper deck, which react injuriously to the stability of the boat and must, necessarily, give rise to great difficulties in the very designing of the submarine. The cylindrical shape of the resistant hull is, in general, undesirable, and its practical realization, when it is a question of the installation of airplane of medium dimensions, would encounter great difficulties.
The construction of light hangars proves more desirable, from many points of view, although they require for their security the installation of special devices. Hangars of this class are constructed in the form of a light, water-tight superstructure, whose structural entirety is assured by maintaining equilibrium between the inner and outer pressures during the submersion of the submarine. Automatic regulation of the outside and inside pressures on the walls of the hangar is secured through the installation in the submarine
of a battery of containers of air compressed to 200 atmospheres and some special devices which permit the air to escape automatically in quantities necessary for the purpose indicated.
The light hangars may be of two types. The first type—a hangar completely insulated from the surrounding medium (Fig. 2)—has an automatic internal pressure regulating valve (a) communicating, on the one hand, with the battery of compressed air containers, and on the other, with the surrounding medium. No sooner does an increase in the depth of submersion take place than the equilibrium between the pressures ceases, and the air from the containers enters the hangar; when the submersion is reduced, the excess air passes out through the safety valve (b) until the inside and outside pressures are equalized. Often, both these functions are fulfilled by one and the same device.
The second type, a hangar which has free communication with the surrounding medium (Fig. 3), has an open pit below in which a float (m) floats freely. This float is connected with the valve regulating the level determined upon in the pit. As the depth of submersion increases, the float rises, opens the valve and permits the entrance into the hangar of the compressed air, which lowers the level of the water in the pit until the float completely closes the valve. In case the depth of submersion diminishes, the excess air escapes freely at the lower edge of the pit, thus regulating the pressure within and without the latter. The depth of the pit is calculated so that the exterior water can in no way enter the hangar, whatever may be the longitudinal or transverse inclinations of the submarine.
Comparing both types of light hangars, it must be recognized that the hangar which communicates freely with the surrounding water offers great advantages over the hangar which is insulated from the water. In the case of the latter, an accident to the regulatory valve, or even its imperfect functioning, may easily lead to the destruction of the hangar walls, due to
the inadmissible difference between the pressures. Any penetration of water into the interior of the hangar inevitably reduces the floatability of the boat. The infiltration of water through the doors of the hangar, which is dependent on numerous chance happenings and often escapes the supervision of the crew, constitutes a serious danger in this connection.
The hangar which communicates freely around the edge of its pit with the surrounding water does not suffer from this defect, for the following reasons. In the first place, the principle of the regulation of the valve by means of a float offers greater security, as experience has shown in numerous cases (carburetors, automatic feed of boilers, etc.). Then, too, the hangar preserves a constant volume, which does not allow any impairing of the floatability of the boat; nor do the infiltrations at the doors offer any greater danger, because, in any case, the water will flow down to the open pit, where the level is maintained constant.
The location of the hangar with respect to the length of the submarine has much influence on the safety of navigation. The best practice is to locate the hangar in the center of the ship, with the doors
facing toward the rear. In such a case, upon the hangar being destroyed by a catastrophe, and the submarine losing its floatability suddenly, it will sink in a horizontal position, that is to say, under circumstances which assure to the crew the best conveniences for maneuvering and taking measures to stop the enforced submersion.
Much less suitable is the location of the hangar in the stern; but the most danger-
ous thing is to place it in the bow of the submarine, with the doors facing forward. This last arrangement was adopted on the English submarine M-2, and, in all probability, constituted one of the principal reasons for the catastrophe which happened to it. The probable picture of the sinking of that boat appears clearly from the attached plan (Fig. 5). To judge from certain data, the airplane hangar on the M-2 was of the light type, insulated from the surrounding water. Under normal conditions of navigation under water (Fig. 5-1), the weight of the submarine (P) was balanced by the floatability (or displacement) of the boat itself (W), while the floatability (J) of the hangar proper was compensated by the corresponding water ballast in the tanks (p). Under such conditions of equilibrium, the submarine navigated with perfect ease; but as soon as the hangar suddenly filled with water, a sudden change must have come about in the navigation. The examination of the sunken submarine by divers brought out the fact that the ship, in an inclined position, was deeply plunged into the bottom of the sea and that the doors of its hangar were open. There are good reasons for supposing that, during progress at high speed, the hangar doors, facing forward, gave way to the pressure of the water. The hangar immediately filled with water and lost its floatability (J) (Fig. 5-2); under the action of the water ballast (p), the submarine began to sink rapidly bow end down, and as the force that was dragging it (R), equal to the weight of the same (P) plus that of the water ballast (p), was greater than the remaining float- ability (W), the boat hurled itself toward the bottom in an inclined position (Fig. 5-3). The electric motors, not stopped in time perhaps, must have contributed to accelerate the movement downward, and the shock against the bottom as a result was terrible. Naturally, under the effect of such a blow, many objects must have been torn from their positions, and the crew of the submarine perished, in the moment of the shock, almost instantaneously.
In order to avoid such an abrupt fall due to damages to the hangar, which may easily occur, in peace time by reason of a collision, in war time from the explosion of a bomb, there should be installed on the submarine a special device or arrangement capable of restoring automatically the floatability of the boat in other parts, as soon as that of the hangar is lost. With this object, floats are installed in the four corners of the hangar which act on the valves of the compressed air tubes (Fig. 3). Normally, these valves remain closed by the weight of the floats; but the water penetrating into the interior of the hangar and causing the floats to float is sufficient to cause the valves to open and the compressed air to rush to the tanks (B1B2), whose volume is calculated according to the capacity of the hangar, empty them, and restore the lost equilibrium.
In spite of their apparent advantages as compared to the hangars having resisting hulls, the light hangars are much more complicated, and, if all their indispensable devices are taken into consideration, they do not deserve their name, inasmuch as the weight of their complete structure must exceed that of a hangar of the heavy type. The fact is that with every alteration in the depth of submersion, a consumption of air takes place: as the submarine submerges to a greater depth, the compressed air leaves the containers; as it rises again, the excess air escapes from the hangar, either through the safety valves (Fig. 2) or by the lower edge of the pit (Fig. 3). Thus, in order to insure the freedom of maneuver of the submarine in navigation under water, it is necessary to equip it, for this sole purpose, with additional batteries of compressed air containers, the quantity of which, according to the volume of the hangar, may double and even treble the set which is generally installed for the maneuvers of emersion of the submarine.
It is true that these containers can, and even should be, installed in the lowest parts of the submarine, so that they do not diminish the stability of the same but, on the contrary, must increase it. This is one important advantage of the light hangars over the heavy ones, for in cases where the latter are used, the principal weight is found at a relatively considerable height.
In view of the defects of both types above described, the question naturally arises: Could not another course be followed to find a simpler solution? We may answer in the affirmative: such a solution can be easily obtained by means of a suitable construction of the airplane.
It should be noted here that the airplane for the submarine ought to be of a special type. In the first place, it must be a hydroplane with floats and devices permitting it to land conveniently on the water and be placed in the hangar. Then, it must have demountable or folding wings, so constructed that their mounting will require the minimum time. By making the airplane of non-rusting materials, which will not suffer from frequent contact with sea water, and placing in it a motor easy to install and take out, the necessity for constructing the hangar with the constant air space disappears. It is then constructed like any other superstructure, with free circulation of water, and only the motor is removed from the airplane and kept in the interior of the resistant hull or in a special, hermetically closing recipient, situated in the hangar itself. In such case all anxiety over preserving the hangar intact is removed, and no catastrophe need be feared as a consequence of its imperfections. For our part, the last solution seems to us the safest one and, probably, will become of more widespread use in the future.
In conclusion, a few words should be said as to the manner of launching the airplane from and re-loading it on the submarine. Based on the experience gained in the placing of airplanes on vessels of the ordinary type, the first installations were equipped with catapults for launching the airplanes and with cranes for lifting them aboard and storing them, in the hangar. Such devices were possessed by the M-2, being made necessary by the location of the hangar in the low of the submarine with the doors facing forward. By arranging the hangar behind the tower, and with the doors facing toward the stern, the said mechanisms would hardly be necessary. The lowering of the airplane to the water can be effected by the submersion of the stern, after the former has been drawn from the hangar and prepared for flight. The raising of the airplane on board from the surface of the sea has now been quite perfected, thanks to the floating canvas which is let out on the sea from the stern of the vessel, and is towed. On the under side of the canvas there are pockets of the same material which, as the vessel advances, form a kind of anchor brake, so that the canvas remains tightly stretched. The hydroplane desiring to return aboard its vessel rises from the rear onto the canvas and is then introduced into the interior of the hangar by a capstan. The maneuver consisting in a submersion followed by an emersion of the stern must facilitate considerably the raising of the airplane on board by the said method. In case the sea is rough, oil may be thrown on the sea from the bow; the oil will calm the surface of the water behind the stern and will facilitate receiving the airplane aboard the submarine.
The problem of providing submarines with airplanes is a new one and will still require many efforts on the part of both naval engineers and the builders of hydroplanes to obtain solutions meeting all practical requirements. As occurs with all new undertakings, the attempts at its solution could not avoid sacrifices of human lives. The M-2 was its first sacrificial offering; but, of course, its loss cannot oblige us to give up the idea of the use of airplanes in submarine navigation. The services which the former are capable of rendering to the latter are too great and obvious. The clear understanding of their utility will induce specialists to continue their work along a definite line.