ds when the mine floats to
the surface. _H._ Iron supports held together (as in small left-hand
diagram) by a band round the mine-casing. The mine goes overboard and
sinks like this to the bottom. The band is then released by a special
device, and the supports drop away, leaving the mine free to float to
the surface (as in small right-hand diagram). _I._ A heavy iron sinker
which acts as an anchor, holding the mine in one position.]

The _Moewe_ left Germany in December, 1916, and crossed the North Sea
amid heavy snow squalls. Proceeding into the North Atlantic, she awaited
a favourable opportunity to approach the British coast. This came one
wild January night with a rising gale and a haze of snow. All her
mines, about 400 in number, were laid off the Scottish coast in the
teeth of a nor'wester. Then, with the "jolly Roger at the fore," she
steamed out on to the wastes of sea lying between the New World and the
Old.

[Illustration: FIG. 24.--Diagram illustrating the effect of tide on a
moored mine. A vessel is approaching a mine _D_, moored to the bottom by
a sinker _H_. The distance from the top of the horns of the mine to the
surface of the sea is approximately 5 feet at low tide, and as the
vessel's draught is 7 feet she would strike the mine. If, however, the
same vessel passed over the same mine a few hours later, at high tide,
the level of the sea would have risen 5 feet, and the mine would then be
10 feet below the surface; in which case the ship would just pass over
in safety. This is known as the "tide difficulty." There is, in
addition, the "dip" of the mine due to the strength of the tidal
current. _E_ and _F_ show what is meant by the dip of a mine. It is the
deflection from the vertical caused by the ebb and flow of the tide. It
frequently causes a mine-field to be quite harmless to passing surface
craft except during the period of slack water between tides.]

* * * * *

We now come to the mines themselves and the method of laying them both
above and below the surface.

A good idea of the shape, size and general characteristics of these
weapons will be obtained from the accompanying diagrams. On being
discharged into the sea they automatically adjust themselves to float
about ten feet below the surface (according to tide) and are anchored to
the bottom by means of a wire mooring rope attached to a heavy sinker.
To describe here the mechanical details of all the different