242 SUBMARINE NAVIGATION. 



The j)ossibility of descending to considerable depths has to be 

 kept in view when deciding on the form and structural arrangements 

 of submarines, which may be subjected accidentally to very great ex- 

 ternal pressiu"e. It is absolutely 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 dithcult of fulfillment, and the ap- 

 proximately circular form usually adopted for the cross sections of 

 submarines favors their resistence to external pressure. 



Under former conditions there was difficulty in remaining long 

 under water w^ithout serious inconvenience from the impurity of the 

 air. Now, by suitable arrangements and chemical ajJi^liances, a 

 supply of pure air can be obtained for considerable periods, sufficient 

 indeed for any operations likely to be undertaken. 



The use of gasoline engines for surface propulsion has many 

 advantages. It favors increase in speed and radius of action, and 

 enables submarines to be more independent and self-supporting. 

 Storage batteries can be recharged, air compressed, and other auxil- 

 iary services performed independently of any " mother '' ship. At the 

 same time it is desirable to give to each group of submarines a 

 supporting ship, serving as a base and store depot, and this has l)een 

 arranged in this county as well as in France. With gasoline engines, 

 care must be taken to secure thorough ventilation and to avoid the 

 formation of explosive mixtures of gas and air, otherAvise accidents 

 must follow. 



Little information is availal)le as regards the success of " peri- 

 scopes ■' and other optical instruments which have been devised for 

 the purpose of enabling those in command of submarines to obtain 

 information as to their surroundings when submerged. In this 

 department secrecy is obviously desirable, and no one can complain 

 of official reticence. From published accounts of experimental Avork- 

 ing abroad as well as in this country, it Avould appear that considerable 

 success has been obtained Avith these oj^tical instruments in compara- 

 tively smooth Avater. It is also asserted that Avhen the lenses are 

 subjected to thorough Avashing by Avave Avater they remain efficient. 

 On the other hand, the moderate height of the lenses aboA'e Avater 

 must expose them to the danger of being wetted by sjjray even in a 

 very moderate sea, and experience in torpedo boats and destroyers 

 places it beyond doubt that the resultant conditions must greatly 

 interfere Avith efficient A^ision. In heavier seas the comparatively 

 small height of the lenses aboA^e Avater 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 experi- 

 ence Avitli these optical appliances, and Ave may be sure that in their 



