THE SUBMARINE OF TO-DAY AND TO-MORROW. 21S 



withstanding its serious disadvantages for submarine service, submarine designers 

 may in the immediate future be forced to employ a steam plant in order to meet the 

 demand for a surface speed of 25 knots or more. With steam-driven vessels, to se- 

 cure equivalent radius of action, the fuel supply must be at least double as compared 

 with Diesel engined vessels. Taking this into account, it would appear that a speed 

 of 25 knots, coupled with a radius of say 1,500 miles at full speed and 3,000 miles 

 at 14 knots, cannot be accomplished on the above limit of displacement without a 

 material sacrifice in submerged qualities. To illustrate this, let us take a concrete 

 case. Starting with a Diesel engined vessel of 1,100 tons surface displacement and 

 20 knots speed, coupled with a normal fuel radius of 1,500 miles at full speed and 

 3,000 miles at 14 knots, and allowing 70 pomds per horse-power for the main engines, 

 we arrive at a weight of approximately 220 tons for main engines and fuel. Now 

 considering a steam-driven 25-knot boat of the same radius of action and corre- 

 sponding speed and assuming that the machinery installation proper can be made on 

 45 pounds per horse-power, we arrive at a total weight of about 366 tons, or an in- 

 crease of 146 tons. The increase of 100 tons in displacement will involve at least 

 an increase of 40 tons in the weight of the hull and fittings, leaving us a net in- 

 crease of not more than 50 tons. Hence, if we are to keep within the limits of 

 the displacements mentioned, we must sacrifice the submerged qualities. Inferior 

 submerged qualities are certainly serious defects from a military standpoint, 

 but a danger of an even graver defect than a moderate decrease in submerged 

 speed and radius is certainly involved in the installation of steam machinery. It has 

 been pointed out above that rapid submergence is an absolutely essential quality and 

 in this respect steam-driven submarines must inevitably be inferior to those driven 

 by internal-combustion engines. Whether and to what extent the inferiority of the 

 steam plant in this respect can be overcome remains entirely a question for the fu- 

 ture, but it is certainly a fact that at the present time the difficulties have not been 

 overcome in France, even in installations of comparatively small power. For the 

 above reasons, the steam plant if adopted at all will be considered as a temporary 

 expedient and the steam engine is certain to be displaced by Diesel engines as soon 

 as the development of the latter permits the attainment of the surface speed re- 

 quired. Because steam units have been developed for other purposes to powers in 

 excess of those which the submarine requires for a speed of 25 knots, it is often as- 

 sumed that there will be no great difficulty in adapting the steam engine to sub- 

 marine propulsion. In the author's judgment, this is an erroneous assumption, 

 since, as a matter of fact, the adaption of the steam drive to the requirements of 

 the submarine involves many a step in the dark and the attempt is likely to result in 

 many disappointments. In fact, as indicated above, it is not beyond the bounds of 

 possibility that the eflFort may result in complete failure, in that, while the surface 

 speed may be obtained, other and vital military qualities may be sacrificed to such 

 an extent as to make it impossible for the vessels to perform the service for which 

 they are designed. 



It had been the author's intention to supplement this discussion with some ac- 



