The role of incendiary vessels changed throughout the age of the modern fire ship. The systematic use of fire ships as part of naval actions peaked around the Third Anglo-Dutch War. Whereas just twenty years before a naval fleet might have six to seven fire ships, by the Battle of Solebay in 1672 both the Dutch and English fleets employed typically between 20 and 30 fire ships, and sometimes more. By this time, however, admirals and captains had become very experienced with the limitations of fire ship attacks and had learned how to avoid them during battle. Great numbers of fire ships were expended during the Third Dutch War without destroying enemy men-of-war, and fire ships had become a way to harass and annoy the enemy, rather than destroy him. The successful use of fire ships at the Battle of La Hogue and Cherbourg in 1692 marked both the greatest achievement of a fire ship attack since the Spanish Armada, and also the last significant success for fire ships. Though fire ships as a specified class sailed with the British Royal Navy for another century, they would never have a significant impact on a naval victory. Once the most feared weapons in naval arsenals, fire ships had declined in both importance and numbers, so that by the mid-18th century only five to six British fire ships would be at sea at a time, and the Royal Navy attempted only four attacks using modern fire ships between 1697 and 1800. Hastily outfitted ad hoc fire ships continued to be used in naval warfare; for example, a large number of fire rafts were used in mostly ineffective attacks on the British fleet by American forces during the American Revolution at Philadelphia, on the Hudson River, and elsewhere. The end of the modern fire ship came in the early 19th century, when the British began to use hastily outfitted fire ships at engagements such as Boulogne and Dunkirk despite the presence of purpose-built fire ships in the fleet. The last modern fire ship in the British Royal Navy was "Thais", the only designated fire ship out of the entire navy of 638 warships when she was converted to a ship sloop in 1808.