It remains, first, to deal with the final link in the old system of defence. The statement that the great routes were left undefended will seem to be in opposition to a prevailing impression derived from the fact that frigates are constantly mentioned as being "on a cruise." The assumption is that they in effect patrolled the great routes. But this was not so, nor did they rove the sea at will. They constituted a definite and necessary part of the system. Though that system was founded on a distinction between defended terminals and undefended routes, which was a real strategical distinction, it was impossible to draw an actual line where the one sphere began and the other ended. Outside the regularly defended areas lay a region which, as the routes began to converge, was comparatively fertile. In this region enemies' cruisers and their larger privateers found the mean between risk and profit. Here too convoys, as they entered the zone, were in their greatest danger for fear of their escorts being overpowered
by raiding squadrons. Consequently it was the practice, when the approach of convoys was expected, to throw forward from the defended area groups of powerful cruisers, and even battleship divisions, to meet them and reinforce their escorts. Outward-bound convoys had their escorts similarly strengthened till they were clear of the danger zone. The system was in regular use both for home and colonial areas. In no sense did it constitute a patrol of the routes. It was in practice and conception a system of outposts, which at seasons of special risk amounted to an extension of the defended areas combining with a reinforcement of the convoy escorts. Focal points of lesser importance, such as Capes Finisterre and St. Vincent, were similarly held by one or two powerful cruisers, and if necessary by a squadron.
As has been already explained, owing to the peculiar conditions of the sea and the common nature of maritime communications, these dispositions were adopted as well for attack as defence, and the fertile areas, for the defence of which a frigate captain was sent "on a cruise," were always liable to bring him rich reward. His mission of defence carried with it the best opportunities for attack.
In the full development of the system patrol lines did exist, but not for the great routes. They were established to link up adjacent defended areas and as a more scientific organisation of the cruiser outposts. In 1805 the Gibraltar and the home areas were thus connected by a patrol line which stretched from Cape St. Vincent through the Finisterre focal area to Cape Clear, with a branch extending to the strategical centre off Ushant. The new system was introduced at a time when we had reason to expect that the French and Spanish fleets were to be devoted entirely to operations in small raiding squadrons against our trade and colonies. Special provision was therefore necessary to locate any such squadrons that might elude the regular blockades, and to ensure that they should be adequately pursued. The new lines were in fact
intelligence patrols primarily, though they were also regarded as the only means of protecting efficiently the southern trade-route where it was flanked by French and Spanish ports.[24]
The whole system, it will be observed, though not conflicting with the main object of bringing the enemy's fleets to action, did entail an expenditure of force and deflecting preoccupations such as are unknown in land warfare. Large numbers of cruisers had to be employed otherwise than as the eyes of the battle-squadrons, while the coming and going of convoys produced periodical oscillations in the general distribution.
Embarrassing as was this commercial deflection in the old wars, an impression appears to prevail that in the future it must be much more serious. It is argued plausibly enough not only that our trade is far larger and richer than it was, but also that, owing to certain well-known economic changes, it is far more a matter of life and death to the nation than in the days when food and raw material did not constitute the bulk of our imports. In view of the new conditions it is held that we are more vulnerable through our trade now than formerly, and that, consequently, we must devote relatively more attention and force to its defence.
If this were true, it is obvious that war with a strong naval combination would present difficulties of the most formidable kind, greater indeed than we have ever experienced; for since with modern developments the demand for fleet cruisers is much greater than formerly, the power of devoting cruisers to trade defence is relatively much less.
It cannot be denied that at first sight the conclusion looks irreproachable. But on analysis it will be found to involve two assumptions, both of which are highly questionable. The first is, that the vulnerability of a sea Power through its maritime trade is as the volume of that trade. The second is, that the difficulty of defending sea-borne trade is also as its volume—that is to say, the larger the amount of the trade, the larger must be the force devoted to its protection. This idea indeed is carried so far, that we are frequently invited to fix the standard of our naval strength by comparing it with the proportion which the naval strength of other Powers bears to their sea-borne trade.