Duff's next ship was the 50-gun , which he joined in 1755. He spent several years cruising, either independently or as part of the main fleet, and in 1758 was part of Commodore Richard Howe's squadron defending the expeditions against St Malo, Cherbourg and St Cas. He became senior officer of a small squadron stationed off Brittany in 1759, watching the French fleet in Morbihan, while a fleet under Edward Hawke blockaded Brest, France. While at anchor in Quiberon Bay on 20 November, his scouts reported a large French fleet to the south of Belle Île. Duff hurried his squadron, consisting of four 50-gun ships and four frigates, out to sea while the French chased them. Before they could be caught, the main fleet under Hawke came up and overran the French, defeating them in the decisive Battle of Quiberon Bay.