and need no "mother ship" or tender. But if submarines achieve
such size, they will be more expensive to build and run than
battleships--and will be, in fact, submersible battleships. In
other words, the submarine cannot displace the battleship, but may
be developed and evolved into a new and highly specialized type
of battleship.

The necessity for operating at long distances from a base carries
with it the necessity for supplying more fuel than even a battleship
can carry; and this means that colliers must be provided. In most
countries, the merchant service is so large that colliers can be
taken from it, but in the United States no adequate merchant marine
exists, and so it is found necessary to build navy colliers and
have them in the fleet. The necessity for continuously supplying
food and ammunition to the fleet necessitates supply ships and
ammunition ships; but the problem of supplying food and ammunition
is not so difficult as that of supplying fuel, for the reason that
they are consumed more slowly.

In order to take care of the sick and wounded, and prevent them from
hampering the activities of the well, hospital ships are needed.
Hospital ships should, of course, be designed for that purpose
before being constructed; but usually hospital ships were originally
passenger ships, and were adapted to hospital uses later.

The menace of the destroyer--owing to the sea-worthiness which this
type has now achieved, and to the great range which the torpedo
has acquired--has brought about the necessity of providing external
protection to the battleships; and this is supplied by a "screen"
of cruisers and destroyers, whose duty is to keep enemy destroyers