In November 1781, the Admiralty had received intelligence that a large convoy was preparing to sail from Brest under Admiral de Guichen. The convoy was composed of transports carrying naval supplies for the West Indies and the French fleet in the East Indies. "Agamemnon" was part of Admiral Richard Kempenfelt's squadron of 18 ships (11 of which mounted 64 or more guns), which he commanded from . Kempenfelt was ordered to intercept the convoy, which he did in the afternoon of 12 December in the Bay of Biscay, approximately south-west of Ushant. With the French naval escort to leeward of the convoy, Kempenfelt attacked immediately, capturing 15 of the transports before nightfall. The rest of the convoy scattered, most returning to Brest; only five transports reached the West Indies.