onsisted
principally of either independent attacks with the aid of hydrophones
and depth charges, or, more frequently, the assumption of an innocent
air in order to induce the submarine to open the attack at close range.

[Illustration: THE RESULT OF A DIRECT HIT

A photograph left by the Germans in Ostend showing a coastal motor boat
washed ashore after the great raid.

_Thornycroft & Co., Ltd._]

In many respects this proved the most effective method of anti-submarine
warfare. Not only did it frequently cause the under-water craft to rise
to the surface and commence the attack by gun-fire, in order not to
expend a valuable torpedo on what appeared to be an unarmed and helpless
ship, but it also produced a _moral_ effect throughout the German
submarine flotillas.

When a few U-boats had been either sunk or damaged in this way the news
that every Allied ship was heavily armed circulated among the enemy
personnel, and they became very nervous of attacking in any position
except totally submerged. This meant the loss of at least one torpedo,
out of from five to ten carried, for every attack made, whether
successful or unsuccessful, and the latter were predominant.

It soon became apparent that either they must risk surface attacks and
so save their torpedoes, or else curtail their cruises to meet the rapid
expenditure of their only submarine weapon. This does not, of course,
cover the activities of under-water mine-layers, whose nefarious purpose
consisted simply of laying their mines wherever they appeared most
likely to catch Allied shipping. These craft were usually armed with
torpedoes as well as mines, to enable them to continue the work of
destruction when the cargo of the latter had been safely laid. In this
way the problem of combating the German submarine offensive resolved
itself into two parts, one being to checkmate the commerce raider and
the other the mine-layer. With the second of these difficulties we shall
deal in a later chapter.

Many merchantmen, both Allied and neutral, owed their escape to this
camouflage warfare, which was brought to a high pitch of perfection and
daring in the now famous mystery ships.

What may be said to form the second method of anti-submarine warfare was
the decoy or camouflage system. Of primary importance in this category
were the mystery ships already described, but there were also
innumerable other _ruses de guerre_ which increased its efficiency.

To describe on