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] [24] It should be said that Cornwallis did not regard this system as new except for the extension from Finisterre to St. Vincent, which Nelson advised. In acknowledging the order from Ushant he wrote, "The instructions ... are nearly the same as have generally been given. I can therefore only guess why a copy of the order was sent to me."--_Admiralty, In-Letters_, 129, 28 September 1805. 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.