e.

[7] For a careful study of the effect of the submarine on the old
theories of sea power see _Submarines and Sea Power_, by Charles
Domville-Fife (Messrs George Bell & Sons, Ltd., London, and Messrs
Lippincotts, New York.).

CHAPTER XI

THE MYSTERIES OF GERMAN MINE-LAYING EXPLAINED

TO those unversed in modern war it may have appeared strange that,
although the Allied navies held command of the sea from the opening of
the Great War in 1914 to the signature of Peace in 1919, the Germans
were nevertheless able to lay several thousand mines every year off the
coasts of England, France and even the most distant colonies and
dominions. It often occurred that harbour entrances and narrow fair-ways
were repeatedly mined, notwithstanding a vigilant day-and-night watch
from the bridges, look-outs and decks of many patrol ships cruising or
listening in the vicinity.

The explanation is that the mines were laid by large submarines capable
of approaching the coast, laying their deadly cargo from specially
constructed stern tubes and retreating to comparative safety far out in
the broad ocean, without rising more than momentarily to the surface for
the purpose of observation.

[Illustration: A CAPTIVE MINE-LAYING SUBMARINE

U.C. 5 off Temple Pier, London.

_Sport and General_]

This, it may be said, did not absolve the ships listening on their
hydrophones, who should have been able to detect the approach of a
submarine from the sound of her engines. During the first year of war
the hydrophone was a very imperfect instrument, and although the sound
might be heard it was quite impossible to tell from what direction it
was coming. Later on, when the listening appliances had been greatly
improved, there still remained two detrimental factors. The noise of
breakers beating against rocks, sands or other obstructions destroyed
much of the value of these instruments when used close inshore. On dark
and rough nights the roar of wind and sea and the lurching of the vessel
rendered subaqueous sounds extremely difficult to detect; and in a
fair-way or channel used by surface shipping it was frequently
impossible, even in fine but dark weather, to tell if the sound coming
up from the sea emanated from a surface ship or a submarine.

If, in the latter case, the patrol ship started her own engines and
moved forward in the darkness to ascertain from whence the noise came,
she gave away her presence to the hostile submarine,