tions of under-water craft
with their torpedoes and mines. There are, however, several recognised
methods of attack and defence employed by surface ships in this newest
form of naval warfare.

When the new navy took the seas in 1914-1915, bases were established not
only round the coasts of the British Isles, but also in the more distant
seas. The principal danger zones were, however, the North Sea, the
English Channel, the Irish Sea, the Mediterranean and the eastern
portion of the North Atlantic. It was through these waters that every
hostile submarine must pass on its voyage out and home.

This geographical factor restricted the theatre of major operations to
some 180,000 square miles of sea. Minor offensive measures might have to
be adopted against individual U-boats cruising at long distances from
their bases, as actually occurred off the United States coast, but the
fact of Germany possessing large submarine bases only along her own
North Sea coast, and temporary ones on the Flanders littoral, enabled a
concentration of Allied anti-submarine craft to be made in the narrow
seas which afforded the only means of entry and exit to and from those
bases.

The same may be said of Austria in the Adriatic and of Turkey behind the
Dardanelles.

This favourable combination of circumstances would not occur if (however
unthinkable) England, France or the United States were ever to wage a
rigorous war against shipping. The large number of oversea naval bases
possessed by these Powers would cause every sea to become a danger zone
within a few hours of the commencement of hostilities. No effective
concentration of hostile surface craft would be possible with the zone
of operations spread over the water surface of the entire globe, and if
the bases themselves were secured by predominant battle fleets, or
numbers of heavily armed monitors, the seas would quickly become
impossible for purposes of hostile transport.

This geographical restriction of the German and Austrian danger zones
made effective concentration of the Allied anti-submarine fleets and
their devices possible. The 180,000 square miles of sea, forming the
theatre of major operations, was, on special charts, divided into areas,
comprising a few hundred square miles of sea. Each area was given a
distinctive number, and a base was established for its own patrol and
minesweeping fleet.

The areas themselves were again subdivided on special charts into
squares or se