concealed, and how shall the crew endure the excessive temperature to which coal fires with little ventilation would subject them? Fortunately, the problem of power for propulsion is much simplified by the fact already mentioned, that for the most part, even a submarine boat lives and moves and has its being on the surface. When at the surface, steam power may be used as on any boat. Many of the earlier boats were thus equipped with boilers and steam engines. These served not only for surface propulsion, but were used also to store up
energy in the form of electricity or compressed air to be available as power when diving.
Nowadays gasoline and oil motors have been so perfected and they allow such economy of fuel space and withal such freedom from the dust, smoke and heat incident to a steam plant that they are coming into very general use, both afloat and ashore, where moderate amounts of power are required. Both the 'Holland' and the 'Argonaut' are equipped with gasoline engines. As these require for their operation much larger quantities of air than can be conveniently supplied from compressed air tanks, wherever concealment is necessary
