First Battle of Ushant

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. His flagship, the 104-gun Ville de Paris, was next in line to the fleet flagship Bretagne. 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]

Battle of Martinique

Luc Urbain de Bouexic, comte de Guichen (1712–1790).

In January 1780, Guichen was sent to the West Indies with a strong squadron. On 17 April to the leeward of Martinique, Guichen's fleet met a force under Rodney, leading to the Battle of Martinique.^[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]

Combat de la Dominique, 17 Avril 1780, by Auguste Louis de Rossel de Cercy (1736–1804).

Two inconclusive actions followed on 15 May and 19 May 1780.^[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. Guichen's second-in-command, Sade de Vaudronne, died at sea as the fleet arrived.^[1]

1781 action in the Bay of Biscay

In December 1781, Guichen was tasked to carry stores and reinforcements to the West Indies. On 12 December, British Admiral Kempenfelt intercepted Guichen's squadron in the Bay of Biscay through a temporary clearance in a fog, at a moment when Guichen's warships were to leeward of the convoy, and attacked the transports at once, yielding the Second Battle of Ushant. Kempenfelt captured twenty of the transports and forced the others to retreat to port. Having failed his mission, Guichen then also returned to port. 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.^[1]