272 POPULAR SCIENCE MONTHLY 



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 

 consideration. 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 exaggerated 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. For 

 these reasons, it is probable that while speeds at the surface will be 

 increased, under-water 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 ver- 

 tical movements has been secured by means of skilled operators, and 

 that a constant but moderate depth below the surface can be main- 

 tained. 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 favor, 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 structural arrangements of 

 submarines, which may be subjected accidentally to very great external 

 pressure. 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 difficult of fulfillment, and the approximately 

 circular form usually adopted for the cross-sections of submarines 

 favors their resistance to external pressure. 



Under former conditions, there was difficulty in remaining 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 ad- 

 vantages. It favors increase in speed and radius of action, and enables 

 submarines to be more independent and self-supporting. Storage 



