hant and naval vessels throughout
the war.

Methods of detection depended on both sight and sound. Efficient
lookout systems on shipboard, with men assigned to different sectors
so as to cover the entire horizon, made it possible frequently
to detect a periscope or torpedo wake in time to change course,
bring guns to bear, and escape destruction. According to a British
Admiralty estimate, in case a submarine were sighted the chances
of escape were seven to three, but otherwise only one to four.
Aircraft of all kinds proved of great value in detecting the presence
of U-boats, as well as in attacking them. Hydrophones and other
listening devices, though at first more highly perfected by the
enemy, were so developed during the war as to enable patrol vessels
to discover the presence and even determine the course and speed of
a submerged foe. Along with these devices, a system of information
was organized which, drawing information from a wide variety of
sources, enabled Allied authorities to trace the cruise of a U-boat,
anticipate its arrival in a given locality, and prophesy the duration
of its stay.

Among methods of destruction, the mounting of guns on merchantmen
was chiefly valuable, as already suggested, because of its effect
in forcing submarines to resort to illegal and barbarous methods
of warfare. Hitherto, submarines had been accustomed to operate an
the surface, board vessels, and sink them by bombs or gunfire. Visit
and search, essential in order to avoid injury to neutrals, was now
out of the question, for owing to the surface vulnerability of the
submarine it might be sent to the bottom by a single well-directed
shot. In brief, the guns on the merchant ship kept submarines beneath
the surface, forced them to draw upon their limited and costly
supply of torpedoes, and hindered them from securing good position
and aim for torpedo attack.

Much depended, of course, upon the range of the ship's guns and
the size and experience of the gun-crews. When the United States
began arming her ships in March, 1917, she was able to put enough
trained men aboard to maintain lookouts and man guns both night
and day. A dozen or more exciting duels ensued between ships and
U-boats before the latter learned that such encounters did not
repay the risks involved. On October 19, 1917, the steamer _J.
L. Luckenbach_ had a four-hour running battle with a submarine in
which the ship fired 202 rounds and the pursuer 225. The lat