he mobility, but the mobility for the force, which it
subserves. Force without mobility is useful; even though limited, as
in coast fortifications; mobility without force is almost useless for
the greater purposes of war. Consequently, when it is found, as is
frequently the case, that one must yield somewhat, in order to the
full development of the other, it is extreme mobility, extreme speed,
which must give way to greater force.

This caution may seem superfluous, but it is not so; for in the
popular fancy, and in the appreciation of the technical expert, and
to some extent also in the official mind as well,--owing to that
peculiar fad of the day which lays all stress on machinery,--mobility,
speed, is considered the most important characteristic in every kind
of ship of war. Let the reader ask himself what is the most pronounced
impression left upon his mind by newspaper accounts of a new ship. Is
it not that she is expected to make so many knots? Compared with that,
what does the average man know of the fighting she can do, when she
has reached the end of that preposterously misleading performance
called her trial trip? The error is of the nature of a half-truth, the
most dangerous of errors; for it is true that, as compared with land
forces, the great characteristic of navies is mobility; but it is not
true that, between different classes of naval vessels, the swiftest
are the most efficient for control of the sea. Force is for that the
determining element.

Keeping these relations of force and mobility constantly in mind,
there is a further consideration, easily evident, but which needs to
be distinctly stated and remembered. When a ship is once built, she
cannot be divided. If you have on land concentrated ten thousand men,
you can detach any fraction of them you wish for a particular purpose;
you can send one man or ten, or a company, or a regiment. You can, in
short, make of them any fresh combination you choose. With ships, the
least you can send is one ship, and the smallest you have may be more
than you wish to spare. From this (as well as for other reasons)
arises a necessity for ships of different classes and sizes, which
must be determined beforehand. The determination must be reached not
merely by _a priori_ reasoning, as though the problem were wholly new;
but regard must be had to the experience of the past,--to the teaching
of history. History is experience, and as such underlies progress,
just as t