DEFENCE SHIPS

In addition to all these types of anti-submarine craft there were,
forming part of the auxiliary fleet, over 300 ships, mostly trawlers and
drifters, engaged in maintaining the great lines of boom defences,
closing vast stretches of sheltered waters frequented by the battle
fleets, and a considerable number of examination ships, staffed by
interpreter officers, whose duty it was to examine all neutral shipping
passing through the 10,000 miles of the blockade.

* * * * *

These, then, were the ships of the new navy, and their formation into
flotillas, or units, was usually accomplished by grouping four or five
vessels of similar type together under the command of the senior officer
afloat--mostly a lieutenant R.N.R. or R.N.V.R. In the case of
minesweepers the unit nearly always consisted of an even number of
ships, because their work was carried out in pairs, and with M.L.'s it
usually consisted of five boats, as this was the number required for the
intricate tactical work of submarine chasing.

There were, of course, units from the United States, French, Japanese,
Italian and Brazilian navies, in addition to the formidable British
armada.

The auxiliary units were all based on one or other of the fifty odd war
stations which encompassed not only the coasts of Great Britain and
Ireland, but also the littoral of every land in our world-wide Empire.
The numbers given here do not include the local fleets of purely
colonial naval bases, nor the large flotillas of destroyers and "P"
boats operating in home and foreign waters in conjunction with the
auxiliary navy. If these were incorporated the anti-submarine fleets
would be almost doubled.

Now that the reader is familiar with the _raison d'etre_ of the new
navy, the personnel, the ships and their formation into fleets, the
scope and limitations of their activity, and of the losses they
sustained, the way is clear for a description of the curious weapons
used, the mysteries of anti-submarine warfare, and the bases themselves
before entering the zone of war and seeing something of the actual work
of the auxiliary navy.

FOOTNOTE:

[3] _Yachting Monthly_ and _R.N.V.R. Magazine_, August, 1917.

CHAPTER V

THE HYDROPHONE AND THE DEPTH CHARGE

OF all the weapons used in the anti-submarine war the two most important
were the _hydrophone_ and the _depth charge_. They were employed in
conjunction with each other a