THE SUBMARINE OF TO-DAY AND TO-MORROW. 209 



rate and the fresh water and provision supply must be four and one-half times as 

 great. This, however, does not tell the whole story, since reasonably comfortable 

 conditions for surface navigation for extended periods in rough water or very 

 cold weather involve alterations in the design, which, if not compensated for by ad- 

 ditional displacement, would reduce the submerged speed and radius. For in- 

 stance, the percentage of surface buoyancy which would be adequate with a smaller 

 radius would, other things being equal, not be adequate in the case of the larger 

 radius. An increase in this, without increase in displacement, would involve a de- 

 crease in submerged speed and radius. Again, even if the supposedly fixed sub- 

 merged qualities were sacrificed to increase the habitability, we must remember 

 that absolute displacement is in itself a large factor. In other words, having in 

 view the weather conditions which must be met, there is probably some minimum 

 limit of surface displacement, even when substantial sacrifices of other qualities are 

 made in favor of habitability. 



Having thus briefly outlined the design problems flowing from the purely mil- 

 itary considerations, let us turn now to the engineering questions involved. As- 

 suming certain speeds, radii and armament as rigid requirements, it is obvious 

 that the displacement must vary according to the type of machinery installed and 

 the amount of attention paid in the design to questions of access and reliability. 

 The most important items in this connection are of course the main engines and the 

 storage batteries. In each case reliability and long life are in conflict with compact- 

 ness and light weight. In these important respects, there is as yet no uniformity 

 of practice in the diflferent navies of the world. In certain continental countries, 

 notably Germany, the extreme of lightness and compactness is sought, accessibility is 

 sacrificed, and a very highly trained personnel is relied on for reliability. The wide 

 range of practice is illustrated by the fact that the weight in pounds per horse-power 

 of the main engines of the single-acting Diesel type almost universally used varies 

 from 50 to 100. In the case of storage batteries, the weight per motor horse-power 

 at the one hour rate of discharge varies from 131 to 253 pounds. The smaller figure 

 represents the extreme case, where the durability of the battery is sacrificed to capac- 

 ity. The heavier of the two batteries is in fact expected to have a service life at 

 least three times as great as the lighter. 



Quite aside from the type of machinery adopted, the matter of access and 

 roominess in general is of great importance, and finally we must in addition con- 

 sider the demands made by safety features, including elaborate bulkhead sub-divi- 

 sion, as well as the installation of special fittings and appliances, such as submarine 

 signals and the like. 



To illustrate the aggregate efifect of such considerations, we may compare a 

 comparatively simple design of the date of 1910 with a very recent one. The early 

 design has the following characteristics: — 



