Next, "Charlestown" took part in the Action of 21 July 1781. She was one of five Royal Navy ships escorting a convoy of 13 colliers and merchant vessels. The escorts also included the two sloops-of-war "Allegiance" and "Vulture", the armed transport "Vernon", and "Jack", another small armed merchant ship. The convoy was off the harbor of Spanish River, Cape Breton, Nova Scotia (present-day Sydney, Nova Scotia), or Île Royale, when it came under attack from two French frigates "Astrée", commanded by La Pérouse, and , commanded by Latouche Tréville, resulting in the Naval battle of Louisbourg. The French captured "Jack". "Charlestown" struck to the French frigates but they were unable to take possession of her; French accounts state that she escaped in the dark. The French lost six men killed and 34 wounded; the British lost some 17 or so men killed and 48 wounded. "Charlestown" alone lost 8 men killed, including Evans, and 29 men wounded. The merchant vessels and their cargoes of coal entered Spanish River safely. "Charlestown" and the sloops sailed back to Halifax.