1913] SUBMARINE Boats 135 
the boat comes to the surface and steam is available from the primary 
boiler, the soda lye may again be concentrated by evaporation of the 
water which it has absorbed, and the boat is ready for another sub- 
merged run. This plan offers the advantages that there is no change 
of motor, the same engine being used under water as on the surface, 
and there are no products of combustion. The machinery can be forced 
without difficulty and relatively high power attained both in light and 
submerged condition. No electric motor is needed. On the other hand, 
the system requires the addition of special soda-boilers and a hot water 
reservoir; the plant occupies so much space that the available weight 
cannot be fully utilised; the centre of gravity of the machinery is high 
and requires extra ballast to be carried; the radius of action on the 
surface is necessarily smaller than with an explosion motor; there is 
likely to be a strong corrosion due to the soda, and isolation for heat 
will probably cause difficulties. The soda-boiler plant appears, how- 
ever, more promising than other power plants so far proposed for this 
purpose. 
ARMAMENT. 
The principal armament of submarine boats is the Whitehead 
torpedo. English boats of the F-class are said to carry six 21 in. tubes 
and French boats of the latest type eight tubes. Recently large sub- 
marine boats have been equipped with an armament of light guns in 
disappearing mountings. Later English boats carry two 3-in. guns so 
mounted that they can be used against air-craft as well as against 
other vessels. When not in use, the guns and mounts are housed in 
the superstructure. 
Attempts have been made to design mine-laying submarine boats, 
a problem which is evidently of considerable interest. As far as known, 
Russia is the only power that prior to the war had built a boat for this 
purpose, viz., the Krab, designed for dropping mines when in surface 
condition. A boat so designed that mines could be dropped when in the 
submerged condition would be of greater value, but there are technical 
difficulties in releasing mines under water, in compensating for their 
weight and in determining their exact location. 
SIGNALLING. 
The faculty of communicating with other vessels whether on the 
surface or submerged is one of great military importance for the sub- 
marine boat. For service on the surface wireless telegraphy has been 
successfully used for several years, but for submerged service it is only 
quite recently that means of signalling has been devised which seem to 
