our coasts, leaving the bigger types of ships on the parent
stations, and the operations were enabled to be considerably
extended. Of course, certain ships were wrecked when gales of
unprecedented violence sprung up; but the output of envelopes,
planes and cars was by this time so good that a ship could be
replaced at a few hours' notice, and the cost compared with
building of additional sheds was so small as to be negligible.

From the month of April, 1917, the convoy system was introduced,
by which all ships on entering the danger zones were collected at
an appointed rendezvous and escorted by destroyers and
patrolboats. The airship was singularly suitable to assist in
these duties. Owing to her power of reducing her speed to
whatever was required, she could keep her station ahead or abeam
of the convoy as was necessary, and from her altitude was able to
exercise an outlook for a far greater distance than was possible
from the bridge of a destroyer. She could also sweep the surface
ahead of the approaching convoy, and warn it by wireless or by
flash-lamp of the presence of submarines or mines. By these
timely warnings many vessels were saved. Owing to the position
of the stations it was possible for a convoy to be met by
airships west of the Scilly Isles and escorted by the airships of
the succeeding stations right up the Channel. In a similar
manner, the main shipping routes on the east coast and also in
the Irish Sea were under constant observation. The mail steamers
between England and Ireland and transports between England and
France were always escorted whenever flying conditions were
possible. For escort duties involving long hours of flying, the
Coastal and C Star types were peculiarly suitable, and at a later
date the North Sea, which could accompany a convoy for the length