"Ethalion" entered service in 1797, operating in the English Channel as part of the Channel Fleet. Soon after commissioning in April under Captain George Countess, "Ethalion" was engaged in chasing a French squadron under Jean-Baptiste-François Bompart intent on invading Ireland during the Rebellion of 1798. Countess kept the French fleet in sight for several days and was able to signal for assistance. This brought a significant force under John Borlase Warren to the region and the French were defeated at the Battle of Tory Island. "Ethalion", with "Melampus", took the 40-gun "Bellone", which the Royal Navy took into service. "Ethalion" had one man killed and three wounded; the French lost 20 men killed. In 1847 the Battle of Tory Island earned for any still surviving crew members the Naval General Service Medal with clasp "12th October 1798".