n away from destroyers, gunboats, and fast
cruisers. Their range of operation was 2,000 miles, and in the early
months of 1915, it was possible for Germany to send two or three of
them from their base in the North Sea to the Mediterranean. Germany
was at the same time experimenting with a larger type, with a
displacement of 1,200 tons and an operating distance of 5,000 miles.

The ordinary submarine in service at the beginning of the war could
remain below the surface for twenty-four hours at least. Reserve
amounts of air for breathing were carried in tanks under pressure, and
in the German type there were also chemical improvements for
regenerating air. Contrary to the opinion of laymen, submerging was
accomplished both by letting water into ballast tanks, and also by
properly deflecting a set of rudders; every submarine had two sets of
rudders, one of which worked in vertical planes and pointed the prow
of the ship either to the left or the right; the other pair worked in
horizontal planes and turned the prow either upward or downward. A
pair of fins on the sides of the hull assisted action in both rising
and diving. The action of water against the fins and rudders when the
ship was in motion was exactly the same as that of the air against the
planes of a kite; to submerge one of the craft it was necessary to
have it in motion and to have its horizontal rudders so placed that
the resistance of the water would drive the ship downward; the reverse
operation drove it upward. And here lay a danger, for if the engines
of a diving submarine stopped she was bound to come to the surface.
Her presence, while moving entirely submerged could be detected by a
peculiar swell which traveled on the water above; if submerged only so
much as to leave the tip of her periscope still showing, the latter
left an easily discernible wake.

The periscope was merely a tube in which there were arranged mirrors
so that anything reflected in the first mirror, the one above the
surface of the water, was again reflected till it showed in a mirror
at the bottom of the tube, within the hull of the vessel, where its
commander could observe it safely. A crew of about twenty-five men was
necessary to operate one of these crafts, and theirs was an unpleasant
duty, first because of the danger that accompanied each submergence of
their vessel; second because of the discomforts aboard. The explosive
engines which drove the craft, whether burning oil or th