The Brest blockade also protected the British supply traffic that sustained it. With larger French warships held in port, fourth rates could escort convoys through the Channel without expecting to face a stronger enemy ship. Particularly valuable convoys sometimes received third-rate escorts. Supplies kept the squadron at sea, while its blockade reduced the threat to the ships bringing those supplies.
Notable Point · 39:35-40:41
Why fourth rates could protect British supply convoys
Keeping larger French warships in port let fourth rates escort British supply convoys against the smaller threats that could still escape.