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



rines of to-morrow." The remainder when considered from the miUtary point of 

 view may be divided into three classes: — 



First, the local or harbor defense submarine. 



Second, the coast defense submarine. 



Third, the offensive submarine. 



The lines of demarcation between these different classes are in fact not very 

 definite. Within certain limits, the harbor defense boats can perform the duties 

 of the coast defense boats. Similarly, the coast defense boats can under certain 

 conditions perform the duties not only of the harbor defense craft, but also of the 

 offensive boats; and again, the offensive boat will usually be found quite well 

 adapted for coast defense purposes. 



Bearing in mind the fact that military considerations include financial ones, 

 it is important to remember : First, that for defensive duties, the only armament 

 of the submarine is the torpedo and its only fighting condition is the submerged 

 condition; second, that in any given area, the greater the number of units, the 

 more efficient the defense ; and third, that increasing the displacement benefits the 

 surface qualities more than the submerged qualities and armament, and, on ac- 

 count of increasing the cost, it decreases the total number of units available. 



Taking all conditions into account and assuming substantial equality as to cli- 

 matic and weather conditions, it would appear that for defense purposes only the 

 most efficient size of unit is dependent on the extent of the coast to be defended. 

 Of course the nature of the approaches to the coast, proximity of possible enemies, 

 configuration of the coast, the location of immediate objectives for the enemy, and 

 other considerations must enter into the matter, but not, it is believed, to the ex- 

 tent of vitiating the general rule. That recent construction programs appear to 

 confirm this rule is perhaps best illustrated by the continued construction of the 

 smallest type, for if we imagine the coast line to be contracted to a single harbor 

 or bay, then the rule would call for the smallest practicable size, which type is in 

 fact found among recent constructions. The only purely harbor defense units of 

 modern construction of which the author has any knowledge were built from the 

 author's design, and commissioned in one of the European navies in 1914. One 

 of these little vessels has already demonstrated its usefulness by torpedoing an 

 enemy destroyer and transport which ventured within its limited radius of action. 

 The characteristics of this type, which was primarily designed for the defense of 

 a certain harbor and bay, are set forth in Table IV. 



