that he had escaped.
If a number of ships were available a few waited over the spot where it
was considered the U-boat was lying, while the others scoured the
surrounding seas in circles trying to pick up the sound of the runaway's
engines if she had escaped in the melee. When nothing further was heard
they returned to the scene and set about the work of systematically
bombing the surrounding sea-bed.

[Illustration: FIG. 10.--Diagram illustrating a depth charge attack on a
submerged submarine. _A._ Motor launch, which has dropped a depth charge
to destroy a submarine _B_ travelling at a depth of 90 feet below the
surface. _C_ is the depth charge sinking as the M.L. steams away from
the danger area. _D_ is the point (80 feet below the surface) at which
it will explode, and _E_ indicates the danger area for the submarine
_B_.]

As many as one hundred depth charges were dropped in quite a small area
of sea and yet a submarine known to have been lying "doggo" in the
locality was not damaged. In cases such as this other means, which will
be described in a succeeding chapter, were then resorted to.

All the foregoing sounds very thorough and hopeful, but in fairness it
must be said that submarine hunting is a heart-breaking task. The
reader may have noticed that the method of depth-charge attack
presupposes the surface vessel to have attained a position almost
directly over the top of her enemy, a manoeuvre extremely difficult of
achievement even with the most efficient hydrophone. Heavy seas, snow
and fog have also to be taken into consideration, to say nothing of
darkness, the presence of a second submarine, a surf-beaten rock or
sandbank and the confusing sounds of passing merchant ships, making a
difficult task more difficult, as will be seen when we come to the
actual fighting.

CHAPTER VI

SOME CURIOUS WEAPONS OF ANTI-SUBMARINE WARFARE

ALTHOUGH modern war has shown that there exists no certain antidote for
the submarine, it nevertheless brought into being many curious weapons
of attack and defence. It is the purpose of this chapter to describe
some of the anti-submarine devices used with more or less successful
results during the protracted naval operations against the Central
Powers.

INDICATOR NETS

Among the most important of these were the immense meshes of wire known
as "indicator nets," which were used to entangle a submarine and then to
proclaim her movements to surface ships waiting to at