THE SUBMARINE OF TO-DAY AND TO-MORROW. 207 



elude such boats in large and increasing numbers. It is also obvious from what 

 has been said above that no standardization as to the size of future submarines 

 is to be expected, since the most effective displacements must necessarily vary 

 with the different conditions met in different cases. This being so, limitations of 

 space here make it necessary to confine our further inquiry into the subject to the 

 case of the United States. 



At the present time, it appears to be the policy of the United States to em- 

 ploy the submarine extensively for coast defense purposes and also to construct 

 it for offensive purposes, either in conjunction with, or independent of, the battle- 

 ship fleet. In view of the great distances which separate us from the most of our 

 probable enemies, and certain special characteristics necessary for the offensive 

 type, it appears safe to conclude that in the immediate future at least two quite 

 separate types will be employed, one of which we shall designate as the "defensive 

 submarine" and the other as the "fleet submarine." While these two types may 

 very well present marked differences in characteristics, nevertheless there are 

 certain general conditions which in the nature of the case must apply to both, and 

 therefore, before attempting to outline the probable future of each type, it will be 

 well to give consideration to these basic conditions. 



The outstanding features characterizing submarine warfare are the following: 



(a) The submerged speed is necessarily inferior to that of the principal ob- 

 jective, viz., the enemy's capital ships. 



(b) The protection of the submarine while engaged is independent of its 

 displacement, except to the extent that increased dimensions impair handiness. 



(c) The torpedo power is not proportionalto displacement. 



All of these considerations emphasize the importance of numbers. Finan- 

 cially speaking, however, large numbers involve limited displacement and hence 

 (within limits) decreased efficiency of the unit. How is this basic difficulty to be 

 adjusted? At first glance, the question seems too involved for any precise treat- 

 ment, but on careful examination we find a reasonable basis for a solution in the 

 fact that physical reasons, for the present at least, place a limit on the submerged 

 speed of from lo to 12 knots. As the chances for a successful attack on a moving 

 target are so vitally affected by the submerged speed, it seems reasonable to adopt 

 the practical maximum as a sine qua non and from that basis build up the de- 

 sign. As the torpedo is the sole reason for the existence of the submarine, it 

 should not be too difficult to fix some irreducible minimum for the number of tor- 

 pedo tubes, which in this case may be put at four. The third absolutely essential 

 quality is the ability to pass from the surface to the submerged condition in a very 

 short period of time. A precise limit as to the permissible period of time is difficult 

 to set, but taking everything into account, we may here regard three minutes as the 

 maximum permissible allowance. By eliminating all frills and non-essentials, it is 

 possible to-day to secure these three primary qualities in a well-balanced design of 

 about 250 tons surface displacement. Starting with this as the lower limit, let us 

 now consider the additional factors, partly military and partly technical, which 

 must determine the final solution. 



