ch therefore furnished an adequate field for the operations
of raiding squadrons. In spite of the elaborate defensive system, such
squadrons might, and sometimes did, intrude by surprise or stealth, and
were then able to set at defiance both convoy escorts and the cruiser
outposts. But, as experience proved, the system of terminal defence by
battle-squadrons made it impossible for such raiding squadrons to remain
long enough on the ground to cause any serious interruption or to do
serious harm. It was only by a regular fleet of superior strength that the
system could be broken down. In other words, the defence could only fall
when our means of local control was destroyed by battle.

So much for the defended areas. With regard to the great routes that
connected them, it has been said they were left undefended. By this is
meant that the security of ships passing along them was provided for, not
by patrols but by escort. The convoy system was adopted, and the theory of
that system is that while vessels are on the great routes they are normally
liable only to sporadic attack, and they are consequently collected into
fleets and furnished with an escort sufficient to repel sporadic attack. In
theory, cruiser escort is sufficient, but in practice it was found
convenient and economical to assign the duty in part to ships-of-the-line
which were going out to join the distant terminal squadron or returning
from it for a refit or some other reason; in other words, the system of
foreign reliefs was made to work in with the supplementary escort system.
Where no such ships were available and the convoys were of great value, or
enemy's ships-of-the-line were known to be out, similar units were
specially detailed for convoy duty to go and return, but this use of battle
units was exceptional.

Such a method of dealing with the great routes is the corollary of the idea
of defended areas. As those areas were fertile and likely to attract
raiding squadrons, so the great routes were infertile, and no enemy could
afford to spend squadrons upon them. It is obvious, however, that the
system had its weak side, for the mere fact that a convoy was upon a great
route tended to attract a squadron, and the comparative immunity of those
routes was lost. The danger was provided for to a great extent by the fact
that the enemy's ports from which a squadron could issue were all within
defended areas and watched by our own squadrons. Still, the guard could