The departure and arrival of the ocean-going shipping in the mouth of the Channel gave the French cruisers their best opportunities for injuring the English trade, despite the cover afforded by the English cruisers. As a rule the convoys were a match for the French in the North Sea and in the Sleeve of the Channel, though they might pick up stragglers and coasting vessels. In the Soundings on the other hand, while the outward-bound fleets were generally too strong for even squadronal attack, there was always the chance that wind or fog might scatter the fleets coming home from distant parts, and there were always the running ships. Twice during the war the regular squadron of cruisers belonging to Dunkirk left its usual stations to work in this fruitful area, either independently or in conjunction with the Brest squadron, and privateers from the ports in Flanders often cruised there as well as those from the Channel and Biscay ports.

The success of the French attack, both by squadrons of ships of force and by Royal ships or privateers working on their own, naturally varied according to the number of cruisers the English Government spared from other services. In the first two years of the war, England being strong in home waters, only privateers and small frigates attacked the trade in the Soundings.