[1] After France entered the War of American Independence, Guichen was appointed to the command of the Channel fleet, which he led in the Battle of Ushant on 27 July 1778.

In March 1779, he was promoted Lieutenant Général des Armées navales, As such he commanded the French van in the Combined fleet of Orvillers and Córdoba from June to September.

[1] During the engagement, both Rodney's Sandwich and Guichen's Couronne were temporarily cut off from their respective fleets and had to bear the brunt of the battle.

[1] With the hurricane season approaching in July, Guichen left the West Indies and returned home, reaching Cadiz in September with a convoy of 95 merchantmen.

He had no opportunity to gain any counterbalancing success during the short remainder of the war, but he was present at the final relief of Gibraltar by Lord Howe.