orted back through
the danger zone to port, and so the game of war continued until months
became years.

All this may sound straightforward and quite simple, but there were
difficulties, to say nothing of dangers, which made it a most arduous
operation. First came the speed problem. Every merchant ship differed in
this important respect, so the speed of the slowest unit became the
speed of the entire fleet, and this reduction made an attack by
under-water craft much easier of accomplishment. Hence the call for
"standard ships," which is a point that should be borne in mind by
future generations as a safeguard against blockade. Then came the
question of destination, which increased the number of escorting
flotillas, and especially ocean cruiser guards, required for a given
number of cargo ships. Next there was the loading and unloading to be
considered, involving long hours and hard work by the men on the
quaysides. This great difficulty was one of the reasons for the
formation of docker battalions. Coaling such big fleets by given times
caused many grey hairs to appear where otherwise they would not have
been. Finally there was the danger of mines having been laid in the
fair-ways leading to the port, which necessitated every convoy being met
by special vessels to sweep the seas in front of each incoming and
outgoing fleet.

[Illustration: FIG. 19.--Diagram showing the convoy system.]

All this and more had to be contended with and overcome before each
convoy was able to sail. Then danger and difficulty came hand-in-hand.
On a bright morning, with probably a fresh breeze blowing and a choppy
sea, the work of the escorting flotilla was easy, but with such climatic
conditions the risk of attack was so great in the waters around the
coasts that troopships usually left harbour under cover of night. No
lights were then allowed, and it will not be difficult for readers to
imagine what it meant to be pounding through a black void in a
fast-moving destroyer, against, possibly, a heavy head sea, with some
twenty or thirty big ships in the darkness and spray around. Thick
sea-mists were the cause of endless trouble, for the safety of an
invisible fleet depended on the vigilance of a half-blind escort. Winter
gales scattered the ships and rendered signals invisible. Attacks came
from the most unexpected quarters and often from more than one point of
the compass at the same time. However, relief came at last, on that
never-to-b