to consider sea power as an entity, and to inquire what are its
leading characteristics, and in what it mainly consists.

There is no trouble in defining what the sea is, but there is a
good deal of trouble in defining what power is. If we look in a
dictionary, we shall find a good many definitions of power; so
many as to show that there are many different kinds of power, and
that when we read of "power," it is necessary to know what kind of
power is meant. Clearly "sea power" means power on the sea. But
what kind of power? There are two large classes into which power
may be divided, passive and active. Certainly we seem justified,
at the start, in declaring that the power meant by Mahan was not
passive, but active. Should this be granted, we cannot be far from
right if we go a step further, and declare that sea power means
ability to do something on the sea.

If we ask what the something is that sea power has ability to do,
we at once perceive that sea power may be divided into two parts,
commercial power and naval power.

The power exerted by commercial sea power is clearly that exerted by
the merchant service, and is mainly the power of acquiring money. It
is true that the merchant service has the power of rendering certain
services in war, especially the power of providing auxiliary vessels,
and of furnishing men accustomed to the sea; but as time goes on the
power contributable by the merchant service must steadily decrease,
because of the relatively increasing power of the naval service, and
the rapidly increasing difference between the characteristics of
ships and men suitable for the merchant service and those suitable
for the naval service.