traffic on to the various
lines for some considerable time ahead, and the masters of ships which
were likely to be for some time at sea were informed of the dates
between which the various lines were to be used, up to a date sufficient
to cover the end of their voyage. There was, therefore, some danger of
this information reaching the enemy if a vessel were captured by a
submarine and the master failed to destroy his instructions in time.
There was also some danger in giving the information to neutrals.

However, the system, which was adopted, did result in a reduction of
losses during the comparatively short time that it was in use, and the
knowledge that patrol craft on the line would be much closer together
than they would be in an approach area certainly gave confidence to the
personnel of the merchant ships, and those who had been forced to
abandon their ship by taking to the boats were afforded a better chance
of being picked up.

Various arrangements were in existence for effecting rapidly a diversion
of shipping from one route to another in the event of submarines being
located in any particular position, and a continual change of the
signals for this purpose was necessary to guard against the possibility
of the code being compromised by having fallen into enemy hands, an
event which, unfortunately, was not infrequent.

Elaborate orders were necessary to regulate coastal traffic, and fresh
directions were continually being issued as danger, especially danger
from mines, was located. Generally speaking, the traffic in home waters
was directed to hug the coast as closely as safe navigation permitted.
Two reasons existed for this, (a) in water of a depth of less than about
eight fathoms German submarines did not care to operate, and (b) under
the procedure indicated danger from submarine attack was only likely on
the side remote from the coast.

Here is an example of the instructions for passing up Channel:

_From Falmouth to Portland Bill._--Hug the coast, following round the
bays, except when passing Torbay. (Directions followed as to the
procedure here.)

_From Portland Bill to St. Catherines._--Pass close south of the
Shambles and steer for Anvil Point, thence hug the coast, following
round the bays.

And so on.

As it was not safe navigationally to follow round the bays during
darkness, the instructions directed that ships were to leave the
daylight route at dusk and to join the dark period route, s