recognized.

The most monotonous and arduous of the airship's duties was the
routine patrol. The ship would leave her shed before dawn and
be at the appointed place many miles away from land. She then
would carry out patrol, closely scanning the sea all round, and
investigating any suspicious object. For hours this might last
with nothing seen, and then in the gathering darkness the ship
would make her way home often against a rising wind, and in the
winter through hail and snow. Bombs were always carried, and on
many occasions direct hits were observed on enemy submarines. A
sharp look-out was always kept for mines, and many were
destroyed, either by gunfire from the airship herself or through
the agency of patrol boats in the vicinity. This was the chief
work of the S.S. ships, and was brought to a high pitch of
perfection by the S.S. Zero. These ships proved so handy that
they could circle round an object without ever losing sight of
it, and yet could be taken in and out of sheds in weather too bad
to handle bigger ships.

The hunting of the submarine has been likened to big-game
hunting, and certainly no one ever set out to destroy a bigger
quarry. It needs the same amount of patience and the same
vigilance. Days may pass without the opportunity, and that will
only be a fleeting one: the psychological moment must be seized
and it will not brook a moment's delay. The eye must be trained
to pick up the minutest detail, and must be capable of doing this
for hour after hour. For those on submarine patrol in a small
ship there is not one second's rest. As is well known, the
submarine campaign reached its climax in April, 1917. In that