122 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE  [VOL. XI. 
illustrate the general standpoint of the problem at that time. It was 
realised that ordinarily a submarine boat would travel on the surface, 
and that diving would only be necessary occasionally, namely when in 
the presence of an enemy. Hence the boat was designed essentially 
for work on the surface and was given a form very similar to that of a 
Thornycroft torpedo-boat. A large self-bailing superstructure was 
fitted on the top, by which a good freeboard and longitudinal stability 
and hence good seagoing capability were secured. The total reserve 
buoyancy was about 33 per cent. of the displacement in light condition, 
half of which was obtained by emptying internal ballast tanks, the 
other half was due to the self-bailing superstructure which was pro- 
vided with valves that could be closed watertight. The propulsion 
was to take place on the surface by steam-power and in the submerged 
condition by electric accumulators. A combination of electric power 
for submarine propulsion with another distinctly different source of 
power for the surface secured at once the military qualities of high 
speed and great radius of action necessary for bringing the boat to the 
field of operation of the enemy, and invisibility and perfect protection 
by going submerged when in the presence of the enemy. The design 
provided for an armament of two Whitehead torpedo tubes in the bow, 
giving great power of attack. 
The type thus proposed, where principal importance was attached 
to service in the surface condition, was later perfected, and boats designed 
on this principle are now generally referred to as ‘‘submersibles’’ in 
contradistinction to “‘submarines’’, which are designed more _par- 
ticularly for submerged work. The characteristics of the two types will 
be more fully discussed later. 
During the “‘eighties’’ a Swede, Mr. T. Nordenfelt, built several boats 
and attained a fair measure of success. He used steam-power for pro- 
pulsion both on the surface and under water, the steam when in the 
latter condition being derived from a store of hot water in a reservoir. 
The system was simple but in order to obtain an appreciable radius of 
action under water a large store of hot water under a high pressure had 
to be carried, whence much space and weight were required. Another 
and serious drawback was that the heat would leak away and the pres- 
sure fall in the hot water reservoir in a relatively short time. The 
Nordenfelt boats were manceuvred on an even keel, and horizontal 
propellers were used to secure immersion and to maintain the desired 
depth. The last Nordenfelt boat, built for the Russian Government, 
was z3¢ts. and the speed was }*kts.* The form was very nearly 
baie upper figures in the fractions refer to the surface condition, the lower figures to the submerged 
condition. 
