nsue from mistaken identity, prevented the U-boats from operating
in pairs. The chief danger encountered by Allied submarines was from
friendly surface vessels. On one occasion an American submarine,
the AL-10, approaching a destroyer of the same service, was forced
to dive and was then given a bombardment of depth charges. This
bent plates, extinguished lights, and brought the submarine again
to the surface, where fortunately she was identified in the nick
of time. The two commanders had been roommates at Annapolis.

[Footnote 1: THE VICTORY AT SEA, _World's Work_, May, 1920, p. 56.]

_Work of the United States Navy_

Having borne the brunt of the naval war for three years, the British
navy welcomed the reenforcements which the United States was able
to contribute, and shared to the utmost the experience already
gained. On May 3, 1917, the first squadron of 6 American destroyers
arrived at Queenstown, and was increased to 50 operating in European
waters in November, and 70 at the time of the armistice. A flotilla
of yachts, ill adapted as they were for such service, did hazardous
duty as escorts in the Bay of Biscay; and a score of submarines
crossed the Atlantic during the winter to operate off Ireland and
in the Azores. Five dreadnoughts under Admiral Rodman from the U.
S. Atlantic fleet became a part of the Grand Fleet at Scapa Flow.

Probably the most notable work of the American navy was in projects
where American manufacturing resources and experience in large-scale
undertakings could be brought to bear. In four months, from July
to November, 1917, the United States Navy constructed an oil pipe
line from the west to the east coast of Scotland, thus eliminating
the long and dangerous northern circuit. Five 14-inch naval guns,
on railway mountings, with a complete train of 16 cars for each gun,
were equipped by the navy, manned entirely with naval personnel, and
were in action in France from August, 1918, until the armistice,
firing a total of 782 rounds on the German lines of communication,
at ranges up to 30 miles.

The American proposal of a mine barrage across the entrance to the
North Sea from Scotland to Norway at first met with slight approval
abroad, so unprecedented was the problem of laying a mine-field 230
miles in length, from 15 to 30 miles in width, and extending at
least 240 feet downward in waters the total depth of which was 400
or more feet. Even the mine barrier at the Straits of Dover had