At the same time a French naval expedition was successfully directed against Cartagena in South America, and under the two blows, both of which depended upon the control of the sea, Spain yielded.
The third military function of the allied navies was the protection of their sea commerce; and herein, if history may be trusted, they greatly failed.

At no time has war against commerce been conducted on a larger scale and with greater results than during this period; and its operations were widest and most devastating at the very time that the great French fleets were disappearing, in the years immediately after La Hougue, apparently contradicting the assertion that such a warfare must be based on powerful fleets or neighboring seaports.

A somewhat full discussion is due, inasmuch as the distress to commerce wrought by the privateers was a large factor in bringing the sea nations to wish for peace; just as the subsidies, which their commerce enabled them to pay the continental armies, besides keeping up their own, were the chief means by which the war was prolonged and France brought to terms.

The attack and defence of commerce is still a living question.
In the first place it is to be observed that the decay of the French fleet was gradual, and that the moral effect of its appearance in the Channel, its victory at Beachy Head, and gallant conduct at La Hougue remained for some time impressed on the minds of the allies.

This impression caused their ships to be kept together in fleets, instead of scattering in pursuit of the enemy's cruisers, and so brought to the latter a support almost equal to an active warfare on the seas.
Again, the efficiency of the English navy, as has been said, was low, and its administration perhaps worse; while treason in England gave the French the advantage of better information.