is device also proved fairly successful, but the dangers of handling
mined nets were considerable and disasters resulted. Furthermore, as
such obstructions could not be securely moored in one spot for very
long, owing to the action of gales and strong tides, it became necessary
for the sake of neutral and allied shipping to maintain a vessel in the
vicinity from which warnings could be issued and repairs to the nets
effected. This partly defeated the object of mined nets, except for the
closing of narrow fair-ways, and their scope as a weapon of attack
became strictly limited.

THE MODIFIED SWEEP

This elaborate and costly anti-submarine device was very widely, but not
altogether successfully, employed by the auxiliary fleet during the
first two years of war. It was nothing more than a long explosive tail
towed submerged by a surface ship, the object being to either drag it
over a submarine resting on the sea-bed, or else, if the under-water
craft was moving, to so manoeuvre the towing surface ship as to swing
the tail close to the U-boat, when the heavy charges of T.N.T. attached
to the armoured electric cable, forming the tail, would be exploded
either by actual contact with the hull of the enemy, or, when
sufficiently close to be effective, by the closing of a firing circuit
on board the surface ship.

[Illustration: FIG. 13.--Diagram showing a vessel towing a modified
sweep. This appliance consists of an armoured electric cable _G_ towed
in vertical loop under the surface. The floats _D_ support the 100-lb.
charges _E_, which have strikers attached. If a submarine _B_ is lying
"doggo" on the sea-bed one or other of these charges may strike her hull
and the whole line then blows up, shattering everything in the
surrounding sea. If the strikers fitted on the charges do not touch the
submarine the whole line can be exploded at will from the surface ship
by closing an electric circuit.]

Excellent in theory but very difficult of accomplishment in actual
practice. The diagram given will explain the details of this elaborate
contrivance, which, however, was soon discarded for more practical
methods, although at least one German submarine is known to have been
destroyed by it.

LANCE BOMBS

These little engines of destruction were intended for fighting at close
quarters, and can be described here in a few lines because of their
guileless simplicity. They consisted of conical explosive bombs on the
ends of broom