on their navies, and in giving so much attention to the education
and training of their officers and enlisted men. To prevent actual
invasion would be comparatively an easy task, one that could be
performed by rows of forts along the coast, supplemented by mines
and submarines. If that is the only kind of defense required, navies
are hardly needed. The army in each country could man the forts
and operate the mines, and a special corps of the army could even
operate the submarines, which (if their only office is to prevent
actual invasion) need hardly leave the "three-mile limit" that
skirts the coasts. If the people of any country do not care to have
dealings outside; if the nation is willing to be in the position
of a man who is safe so long as he stays in the house, but is afraid
to go outdoors, the problem of national defense is easy.

But if the people desire to prevent interference with what our
Constitution calls "the general welfare," the problem becomes
exceedingly complex and exceedingly grave--more complex and grave
than any other problem that they have. If they desire that their
ships shall be free to sail the seas, and their citizens to carry
on business and to travel in other lands; and if they desire that
their merchants shall be able to export their wares and their farmers
their grain, also that the people shall be able to import the things
they wish from foreign countries, then they must be able to exert
actual physical force on the ocean at any point where vessels carrying
their exports and imports may be threatened. Naval ships are the
only means for doing this.

The possibility that an armed force sent to a given point at sea
might have to fight an enemy force, brought about first the sending of
more than one vessel, and later--as the mechanic arts progressed--the
increasing of the size of individual vessels, and later still the
development of novel types.

There are two main reasons for building a small number of large
ships rather than a large number of small ships. The first reason
is that large ships are much more steady, reliable, safe, and fast
than small ships. The second reason is that, when designed for
any given speed, the large ships have more space available for
whatever is to be carried; one 15-knot ship of 20,000 tons normal
displacement, for instance, has about one and a half times as much
space available for cargo, guns, and what-not, as four 15-knot
ships of 5,000 tons each. These