What a Good Power Plant Is.—There are certain things an engine must be and do to make it useful for driving a submarine boat, and among the chief ones are:
(1) It must be as small and as light as possible and still have great strength.
(2) It must develop a lot of power for its size and weight.
(3) It must use a small amount of fuel for the power it develops.
(4) The fuel it uses must not be bulky for the power it gives.
(5) It must not give off odors.
(6) All working parts must be easily getatable, and
(7) It must not give off poisonous gases, or vapors that ignite easily, for either of these are dangerous.
From this you will see that it is not an easy matter to make an engine for a submarine that will have all of these good features, but inventors have come pretty close to it, as you will presently learn.