June 29, 1905] 



NA 7 URE 



water displaced. If the weight of the vessel exceeds by 

 ever so small an amount the weight of water displaced, 

 that excess constitutes an accelerating force tending to 

 sink the vessel deeper. On the contrary, if the weight of 

 water displaced exceeds by ever so small an ainount the 

 total weight of the vessel, a vertical force is produced 

 tending to restore her to the surface. In these circum- 

 stances, it is obvious that if the admission or expulsion of 

 water from internal tanks (or the extrusion or withdrawal 

 of cylindrical plungers for the purpose of varying the dis- 

 placement) were the only means of controlling vertical 

 movement, it would be exceedingly difficult to reach or to 

 maintain any desired depth. This difficulty was antici- 

 pated on theoretical grounds, and has been verified on 

 service — in some cases with considerable risks to the ex- 

 perimentalists — the submarines having reached the bottom 

 before the vertical motion could be checked. It has con- 

 sequently become the rule for all submarines to be left 

 with a small reserve of buoyancy when brought into the 

 diving condition. Submergence is then effected by the 

 action of horizontal rudders controlled by operators within 

 the vessels. Under these conditions, submergence only 

 continues so long as onward motion is maintained, since 

 there is no effective pressure on the rudders when the 

 vessel is at rest. The smallest reserve of buoyancy should 

 always bring a submarine to the surface if her onward 

 motion ceases, and, as a matter of fact, in the diving 

 condition that reserve is e.xtremely small, amounting to 

 only 300 lb. (equivalent to 30 gallons of water) in vessels 

 of 120 tons total weight. This is, obviously, a narrow 

 margin of safety, and necessitates careful and skilled 

 management on the part of those in charge of submarines. 

 A small change in the density of the water, such as occurs 

 in an estuary or in the lower reaches of a great river, 

 would speedily obliterate the reserve of buoyancy and cause 

 the vessel to sink if water was not e.xpelled from the 

 tanks. Moreover, variations in weight of the submarine 

 (due to the consumption of fuel, the discharge of torpedoes 

 or other causes) must sensibly affect the reserve of 

 buoyancy, and arrangements must be made to compensate 

 for these variations bv admitting equal weights of water in 

 positions that w-ill maintain the " trim " of the vessel. 

 Additional safeguards against foundering have been pro- 

 vided in some submarines by fitting detachable ballast. 

 The more common plan is to make arrangements for 

 rapidly expelling water from the tanks either by means of 

 pumps or by the use of compressed air. In modern sub- 

 marines, with locomotive torpedoes, compressed air is, of 

 course, a necessity, and can be readily applied in the 

 manner described if it is desired to increase their buoyancy. 

 The conditions of stability of submarines when diving 

 are also special. At the surface, owing to their singular 

 form, the longitudinal stability is usually much less than 

 that of ordinary ships. When submerged, their stability 

 is the same in all directions, and it is essential that the 

 centre of gravity shall be kept below the centre of 

 buoyancy. This involves no difficulty, because water- 

 ballast tanks can be readily built in the lower portions of 

 the vessels. Small stability in the longitudinal sense, how- 

 ever, necessitates great care in the maintenance of trim, 

 and in the avoidance of serious moveinents of weights' 

 within the, vessels. Moreover, when a vessel is diving 

 under the action of her longitudinal rudders, she is ex- 

 tremely sensitive to changes of trim, and great skill is 

 required on the part of operators in charge of working 

 the rudders. As the under-water speed is increased, the 

 pressure on the rudders for a given angle increases as the 

 square of the velocity, and sensitiveness to change of trim 

 becomes greater. This fact makes the adoption of higher 

 under-water speed a matter requiring very serious consider- 

 ation. Some authorities, who have given great attention 

 to the construction of submarines, have been opposed to 

 the adoption of high speeds under water, because of the 

 danger that vessels when diving quickly may reach much 

 greater depths than are desirable. Causes of disturbance 

 which might be of small importance when the under- 

 water speed is moderate may have a greatly e.xaggerated 

 effect when higher speeds are reached. Cases are on record 

 where modern submarines in the hands of skilled crews 

 have accidentally reached the bottom in great depths of 

 water, and have had no easy task to regain the surface. 



NO. 1 86 1, VOL. 72] 



For these reasons, it is probable that while speeds at the 

 surface will be increased, under-w^ater speeds will not grow 

 correspondingly. Indeed, the tactics of submarines hardly 

 appear to require high speed under water, seeing that it is 

 an important element in successful attack to make the final 

 dive at a moderate distance from the enemy. It is 

 authoritatively stated that in our submarines complete 

 control of vertical movements has been secured by means 

 of skilled operators, and that a constant but moderate 

 depth below the surface can be maintained. Proposals have 

 been made and successfully applied to small submarines 

 for automatically regulating the depth of submergence by 

 apparatus similar to that used in locomotive torpedoes. 

 For the larger submarines now used such automatic 

 apparatus does not find favour, and better results are 

 obtained with trained men. 



The possibility of descending to considerable depths has 

 to be kept in view when deciding on the form and struc- 

 tural arrangeinents of submarines, which may be subjected 

 accidentally to very great external pressure. It is abso- 

 lutely necessary to success that, under the highest pressure 

 likely to be endured, there shall be rigidity of form, as 

 local collapse of even a very limited amount might be 

 accompanied by a diminution in displacement that would 

 exceed the reserve of buoyancy. This condition is not 

 difficult of fulfilment, and the approximately circular form 

 usually adopted for the cross-sections of submarines favours 

 their resistance to external pressure. 



Under former conditions, there was difficulty in remain- 

 ing long under water without serious inconvenience from 

 the impurity of the air. Now, by suitable arrangements 

 and chemical appliances, a supply of pure air can be 

 obtained for considerable periods, sufficient, indeed, for any 

 operations likely to be undertaken. 



The use of gasolene engines for surface propulsion has 

 many advantages. It favours increase in speed and radius 

 of action, and enables submarines to be more independent 

 and self-supporting. Storage batteries can be re-charged, 

 air compressed and other auxiliary services performed 

 independently of any " mother " ship. At the same time, 

 it is desirable to give to each group of submarines a sup- 

 porting ship, serving as a base and store dep6t, and this 

 has been arranged in this country as well as in France. 

 With gasolene engines, care must be taken to secure 

 thorough ventilation and to avoid the formation of explosive 

 mixtures of gas and air, otherwise accidents must follow. 



Little information is available as regards the success of 

 " periscopes " and other optical instruments which have 

 been devised for the purpose of enabling those in command 

 of submarines to obtain information as to their surround- 

 ings when submerged. In this department, secrecy is 

 obviously desirable, and no one can complain of official 

 reticence. From published accounts of experimental work- 

 ing abroad as well as in this country, it would appear that 

 considerable success has been obtained with these optical 

 instruments in comparatively smooth water. It is also 

 asserted that when the lenses are subjected to thorough 

 washing by wave-water, they remain efficient. On the 

 other hand, the moderate height of the lenses above water 

 must expose them to the danger of being wetted by spray 

 even in a very moderate sea, and experience in torpedo- 

 boats and destroyers places it beyond doubt that the re- 

 sultant conditions must greatly interfere with efficient 

 vision. In heavier seas, the comparatively small height of 

 the lenses above water must often impose more serious 

 limitations in the use of the periscopes and similar instru- 

 ments. Improvements are certain to be made as the result 

 of experience with these optical appliances, and we may be 

 sure that in their use officers and men of the Royal Navy 

 will be as expert as any of their rivals. But when all 

 that is possible has. been done, it must remain true that 

 increase in offensive power and in immunity from attack 

 obtained by submergence will be accompanied by unavoid- 

 able limitations as well as by special risks resulting from 

 the sacrifice of buoyancy and the great reduction in longi- 

 tudinal stability which are unavoidable when diving. 

 These considerations have led many persons to favour the 

 construction of so-called surface-hoats rather than sub- 

 marines. They would resemble submersibles in many re- 

 spects, but the power of diving would be surrendered, 

 although they would be so constructed that by admitting 



