SUBMARINE MINES
If the Russo-Japanese war was the first to fully demonstrate the value
of the explosive mine, the Great European Conflict has certainly brought
this weapon to the forefront in the rapidly growing science of submarine
warfare. During the first few weeks of the naval fighting several
warships, beginning with H.M.S. _Amphion_, and many merchant vessels
representing millions of pounds sterling, were destroyed by these
weapons. Had it not been for the foresight of the British Admiralty in
providing a very large fleet of mine-sweepers, aided by seaplanes, there
can be no doubt but what the shipping of all countries—neutrals and
belligerents alike—would have suffered far greater losses.
[Illustration: LAUNCHING A GERMAN TROTYL MINE.]
[Illustration:
A GERMAN SUBMARINE TROTYL MINE ON THE DECK OF A MINE-LAYER.
These mines contain the famous T.N.T., or Trotyl explosive.
]
The indiscriminate scattering of mines across the trade routes, as
carried on by Germany immediately on the outbreak of war, and before
hardly any of the ships at sea belonging to neutral countries could be
warned to avoid the zone of operations, has never before been so
ruthlessly resorted to by a big civilised power.
The system of defence consists of the mooring of these mines in such
positions as to make it almost impossible for hostile ships to pass
without either striking or coming within the destructive zone of one or
more of them. What are known as _floating mines_ are those set adrift to
be washed about by the tide. They explode immediately on being struck by
a passing vessel, and, of course, do not discriminate between friend and
foe. The systems of destroying hostile mine-fields consist of
_counter-mining_, or placing other mines in the enemy’s field and
destroying it by their explosion, and by _sweeping_. The latter method
is the one mostly employed in modern warfare. The boats taking part in
the _sweep_ place themselves one on each side of the mine-field, and
between them hangs a long wire rope, weighted in the centre to keep it
well submerged. They then move forward, sweeping the mines to the
surface or exploding them harmlessly. It is, however, very dangerous but
highly necessary work.
There are two kinds of submarine mines, one is designed to explode on
being struck by a passing vessel, and is called a _contact mine_, and
the other is fired from the shore by an electric current, and is known
as an _observation mine_. The explosive principally used is wet
gun-cotton or Trotyl, owing not only to the safety with which they can
be stored and manipulated, but also to the fact that they seldom explode
in sympathy with neighbouring mines, requiring to be actually fired. The
importance of this will be more fully realised when it is remembered
that in warfare it is often necessary to explode certain mines over
which hostile ships are endeavouring to pass, while leaving others in
fairly close proximity intact, ready to repel a second invasion or to
destroy ships nearer to them. The actual explosion is caused by an
electric current, either from the shore or from a battery in the mine
itself, causing the detonation of fulminate of mercury in conjunction
with a small priming charge of dry gun-cotton. Mines are often laid in a
series, connected to a battery on the sea-bed in the centre of the line
of defence.
The _observation mine_ is mostly used for defending the approaches to
harbours, as an observer on shore can watch the movements of hostile
warships and explode each mine when the vessel passes over it. _Contact
mines_, on the other hand, are used wherever an enemy’s fleet is likely
to pass. They are anchored to the sea-bed by means of a cable and heavy
weight, and are allowed to float a few feet below the surface. They
explode immediately on contact. At times an unscrupulous or demoralised
enemy will simply throw a number of these mines overboard and allow them
to float at the mercy of wind and tide. They then become a terrible
danger to the shipping of all nations, as once they are left unwatched
it is extremely difficult to tell with any degree of certainty where
they will eventually proclaim their presence by devastating explosions.
Happily for the whole seafaring world, this method is seldom resorted
to, as mines set adrift in this way become a danger to both friend and
foe. In the Russo-Japanese war several ships were destroyed by their own
mines.
There are many different kinds of submarine mines, both of the
observation and the contact type. Some are spherical in shape and others
cylindrical. Some are moored close down to the sea-bed with a very heavy
explosive charge (200‒500 lbs. of gun-cotton), and have a small buoyant
globe floating above them, which, when struck, fires the mine below.
Others, known as secret-mines, are kept continually moored in the
waterways leading to important naval harbours, and are only allowed to
rise sufficiently high from the sea-bed to be struck by passing vessels
in times of emergency. The type most generally used is, however, the
ordinary _offensive contact mine_, which contains a powerful explosive
charge and is anchored in the path of hostile warships. These mines are
usually automatically sown in large numbers over a wide area of sea by
the mine-laying fleets.