in terms of its real basis, there is a period of oars, a period
of sails, and a period of steam.

The classification, it will be seen, is no arbitrary device
invented for the clearer exposition of naval history, but
one that is natural and inevitable. Not only do the
divisions lie between well defined chronological limits, but
they are rooted in the essentials of the art. The essence
of naval strategy is sea endurance, by which is meant the
degree of a fleet's capability of keeping the sea. The
essence of naval tactics is the nature of the motive power;
that is to say, tactics primarily depend upon how far the
movements of the fleet or ship are under human control,
and how far dependent upon conditions that lie beyond it,
or, in other words, whether the units of the fleet are of
free or of subservient movement.

To these essential elements of the art each of the
three periods has its own distinct relation. Each of
them is measurable and determined by the degree of sea
endurance and the degree of mobility exhibited by its
characteristic type of capital ship. The galley was a
vessel of low sea endurance but of highly free movement.
The great-ship, or ship-of-the-line, was of large sea endu-
rance but entirely subservient to the wind for its power of
movement. The steam battleship, while far surpassing
the galley in mobility, approaches the ship-of-the-line in
sea endurance. In the first period, the period of oars, when
the focus of empire lay within the confined waters of
the Mediterranean, we see mobility taking precedence of
sea endurance; in the second, the period of sails, when
the arena of history widens out into the ocean, sea endu-
rance becomes of the first importance; in the third, the
period of steam, when the area of naval action is greater
and the demand for extreme mobility more pressing than
ever, we have the effort to combine both qualities in

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