1905.] on Suhnarine Navigation. 15^ 



the construction of these small submarines. They would necessarily 

 be of slow speed and very limited radius of action, while their efficient 

 working would depend upon the nerve and skill of only two or three 

 men working in a very confined space. 



Progress in mechanical engineering and in metallurgy has been 

 great since Bushnell constructed and used his first submarine in 177G> 

 during the war between the United States and this country. These 

 advances have made it possible to increase the dimensions, speed and 

 radius of action of submarines ; their offensive powers have been 

 enlarged by the use of locomotive torpedoes ; and superior op- 

 tical arrangements have been devised for discovering the position 

 of an enemy while they themselves remain submerged. But it 

 cannot be claimed that any new principle of design has been dis- 

 covered or appHed. From descriptions left on record by Bushnell, 

 and still extant, it is certain that he appreciated, and provided for 

 the governing conditions of the design in regard to buoyancy, sta- 

 bility, and control of the depth reached by submarines. Indeed, 

 Bushnell showed the way to his successors in nearly all these parti- 

 culars, and — although alternative methods of fulfilling essential con- 

 ditions have been introduced and practically tested — in the end 

 Bushnell's plans have in substance been found the best. The laws 

 which govern the flotation of submarines are, of course, identical with 

 those applying to other floating bodies. When they are at rest and 

 in equilibrium they must displace a weight of water equal to their 

 own total weight. At the surface they float at a minimum draught 

 and possess in this " awash " condition a sufficient freeboard and 

 reserve of buoyancy to fit them for propulsion. When submarines 

 are being prepared for " diving " water is admitted to special tanks,. 

 and the additional weight increases immersion, and correspondingly 

 reduces reserve of buoyancy. In some small submarines comparative 

 success has been attained in reaching and maintaining any desired depth 

 below the surface simply by the admission of the amount of water 

 required to secure a perfect balance between the weight of the vessel 

 and all she contains, and the weight of water which would fill the 

 cavity occupied by the submarine when submerged. For all practical 

 purposes and within the depths reached by submarines on service 

 water may be regarded as incompressiUe ; the submarine should, there 

 fore, rest in equilibrium at any depth if her total weight is exactly 

 balanced by the weight of water displaced. If the weight of the vessel 

 exceeds by ever so smaU an amount the weight of water displaced, that 

 excess constitutes an accelerating force tending to sink the vessel 

 deeper. On the contrary, if the weight of water displaced exceeds by 

 ever so small an amount the total weight of the vessel, a vertical 

 force is produced tending to restore her to the surface. Under these 

 circumstances, it is obvious that if the admission or expulsion of water 

 from internal tanks (or the extrusion or withdrawal of cylindrical 

 plungers for the purpose of varying the displacement) were the only 

 means of controlling vertical movement, it would be exceedingly 



