eceding part of this article. The measure of degree is the estimated
force which the strongest _probable_ enemy can bring against you,
allowance being made for clear drawbacks upon his total force, imposed
by his own embarrassments and responsibilities in other parts of the
world. The calculation is partly military, partly political, the
latter, however, being the dominant factor in the premises.

In kind, preparation is twofold,--defensive and offensive. The former
exists chiefly for the sake of the latter, in order that offence, the
determining factor in war, may put forth its full power, unhampered by
concern for the protection of the national interests or for its own
resources. In naval war, coast defence is the defensive factor, the
navy the offensive. Coast defence, when adequate, assures the naval
commander-in-chief that his base of operations--the dock-yards and
coal depots--is secure. It also relieves him and his government, by
the protection afforded to the chief commercial centres, from the
necessity of considering them, and so leaves the offensive arm
perfectly free.

Coast defence implies coast attack. To what attacks are coasts liable?
Two, principally,--blockade and bombardment. The latter, being the
more difficult, includes the former, as the greater does the lesser. A
fleet that can bombard can still more easily blockade. Against
bombardment the necessary precaution is gun-fire, of such power and
range that a fleet cannot lie within bombarding distance. This
condition is obtained, where surroundings permit, by advancing the
line of guns so far from the city involved that bombarding distance
can be reached only by coming under their fire. But it has been
demonstrated, and is accepted, that, owing to their rapidity of
movement,--like a flock of birds on the wing,--a fleet of ships can,
without disabling loss, pass by guns before which they could not lie.
Hence arises the necessity of arresting or delaying their progress by
blocking channels, which in modern practice is done by lines of
torpedoes. The mere moral effect of the latter is a deterrent to a
dash past,--by which, if successful, a fleet reaches the rear of the
defences, and appears immediately before the city, which then lies at
its mercy.

Coast defence, then, implies gun-power and torpedo lines placed as
described. Be it said in passing that only places of decisive
importance, commercially or militarily, need such defences. Modern
fleets ca