Wind and weather could break a close blockade

Brest's geography made blockade an operational problem as well as a contest of numbers. A British force close enough to watch the port was exposed to Atlantic weather, and a storm-driven withdrawal could leave an opening for French ships to sail. Winds and tides made Plymouth a more practical support base than the Channel Islands, regardless of their apparent distance on a map. Brest also stood alongside the Low Countries as one of the strategic approaches from which an invasion threat to Britain might develop. Trying to hold Brest on land would tie down Britain's smaller army against France, so the continuing task fell to a naval squadron.