Isly was a Jean Bart-class protected cruiser built in the late 1880s and early 1890s for the French Navy. The second and final member of the class, Isly and her sister ship were ordered during the tenure of Admiral Théophile Aube as Minister of Marine according to the theories of the Jeune École doctrine. The ships were intended as long-range commerce raiders, and they were armed with a main battery of four 164 mm (6.5 in) guns, were protected by an armor deck that was 50 to 100 mm (2 to 4 in) thick, and were capable of steaming at a top speed of around 19 knots (35 km/h; 22 mph).

Isly initially served with the Reserve Division of the Northern Squadron, spending only part of the year in active service for training exercises. She was deployed to French Indochina from 1895 to 1896 and then again from 1897 to 1899. After returning to France, she joined the North Atlantic station, operating out of Brest. Isly spent the next decade serving in the Atlantic, changing units as the fleet was repeatedly reorganized; she also received new water-tube boilers in 1902. In 1908, she was briefly sent to French Morocco, and the following year she was converted into a depot ship for destroyers. She was struck from the naval register in 1914 and thereafter broken up.

Design work on the Jean Bart class began in 1885 under the direction of the French naval minister, Charles-Eugène Galiber, who wanted a new commerce raiding protected cruiser similar to the earlier Amiral Cécille, albeit smaller and with a smaller secondary battery. By the time French shipyards had responded to requests for design proposals, Admiral Théophile Aube had replaced Galiber as naval minister, but Aube was an ardent supporter of the Jeune École doctrine that emphasized long-range, commerce raiding cruisers. He called for the construction of six large and ten small protected cruisers, though by the end of his tenure in 1887, the program had been reduced to five large, two medium, and six small cruisers. Aube ordered the first two Jean Bart-class cruisers to fulfill the requirements for the first set of large cruisers, and his successor, Édouard Barbey, authorized the third. The two Jean Barts proved to be the last of the initial series of commerce raiders built under the influence of the Jeune École.

Isly was 105 m (344 ft 6 in) long between perpendiculars, with a beam of 12.98 m (42 ft 7 in) and a draft of 6.10 to 6.45 m (20 ft 0 in to 21 ft 2 in). She displaced 4,406 long tons (4,477 t). Her crew varied over the course of her career, amounting to 387–405 officers and enlisted men. The ship's propulsion system consisted of a pair of triple-expansion steam engines driving two screw propellers. Steam was provided by eight coal-burning fire-tube boilers that were ducted into two funnels. Her machinery was rated to produce 8,000 indicated horsepower (6,000 kW) for a top speed of 19 to 19.5 knots (35.2 to 36.1 km/h; 21.9 to 22.4 mph). She had a cruising radius of 3,200 nautical miles (5,900 km; 3,700 mi) at 10 knots (19 km/h; 12 mph).

The ship was armed with a main battery of four 164.7 mm (6.48 in) 28-caliber guns and a secondary battery of six 138.6 mm (5.46 in) 30-cal. guns. All of these guns were placed in individual pivot mounts; the 164 mm guns were in sponsons located fore and aft, with two guns per broadside. Four of the 138 mm guns were in sponsons between the 164 mm guns, one was in an embrasure in the forecastle and the last was in a swivel mount on the stern. For close-range defense against torpedo boats, she carried six 47 mm (1.9 in) 3-pounder Hotchkiss guns and eight 37 mm (1.5 in) Hotchkiss revolver cannon. She was also armed with five 356 mm (14 in) torpedo tubes in her hull above the waterline. Armor protection consisted of a curved armor deck that was 40 to 90 mm (2 to 4 in) thick, along with 120 mm (5 in) plating on the conning tower. The main and secondary guns received 54 mm (2.1 in) thick gun shields.

In 1897, Isly had her heavy military masts replaced with light pole masts in an attempt to reduce topweight. At that time, she also had her bow and stern torpedo tubes removed. Another refit took place in 1909, during which her light armament was standardized to twelve 47 mm guns. The navy considered replacing her boilers in 1910, but decided against it due to the cost.

Isly was ordered on 1 March 1887 and she was laid down at the Arsenal de Brest in Brest, France on 3 July 1887, before the lead ship of her class, Jean Bart, began construction. She was launched on 22 June 1891 and was commissioned on 25 October 1892 to begin sea trials. During her initial testing, she reached a top speed of 18.5 knots (34.3 km/h; 21.3 mph) using forced draft, though the test was conducted in poor weather that reduced the ship's speed by about half a knot. The trials lasted nearly a year, and she was finally placed in full commission for active service on 20 September 1893. Ten days later, she steamed to Cherbourg to join the Escadre du Nord (Northern Squadron). She was assigned to the Reserve Division of the Northern Squadron, which that time included the ironclad Suffren, the coastal defense ships Tonnerre and Fulminant, and the torpedo cruiser Epervier.

The following year, she continued to operate with the squadron. She took part in annual training exercises that year to evaluate the effectiveness of the French coastal defense system. The squadron went to sea on 15 July and began the operations the next day, which lasted until 29 July. The maneuvers demonstrated the usefulness of torpedo boat flotillas in coastal defense, but highlighted that France's coastal defense system in the English Channel was not yet complete. Isly was sent with the cruiser Alger on a cruise to French Indochina in 1895; at that time, the unit also included the cruisers Duguay-Trouin, Forfait, and Beautemps-Beaupré. She remained on station in the Far East into 1896, but was ordered home that year. In 1897, Isly returned to the Far East in company with the recently completed protected cruiser Descartes; they joined the old ironclad Bayard and the unprotected cruiser Éclaireur.

Isly had returned to France by 1899, when she was assigned to the North Atlantic station in Brest on 15 March. The ship was laid up in 1900 for an overhaul that included the replacement of her original wood decks with linoleum-covered steel. She remained out of service through early 1901 and was recommissioned on 8 April for service in the fisheries in the Atlantic. She was assigned to the Naval Division of the Atlantic Ocean, along with the protected cruisers Suchet and Amiral Cécille. Isly operated with the transport vessel Manche, patrolling the fishing grounds off Newfoundland for six months of the year. The next year, Isly was decommissioned for a major overhaul, which included the installation of new water-tube boilers.

In 1908, the Naval Division of the Atlantic was amalgamated with the Northern Squadron, and Isly was transferred to that command, commissioning for service on 1 January in Lorient. By that time, the squadron consisted of eight armored cruisers and four other protected cruisers. Isly was temporarily sent to French Morocco early in the year in company with the armored cruiser Kléber. In 1909, Isly was converted into a depot ship for destroyers, before being decommissioned on 13 March 1911. She was struck from the naval register on 23 November 1911 and used as a depot ship for torpedo boats based in Lorient from late 1911 to 1913. She was then placed for sale, eventually being purchased on 11 April 1914 by Willer Peterson of Copenhagen, Denmark, to be broken up.

• Barry, E. B. (1895). "The Naval Manoeuvres of 1894". The United Service: A Monthly Review of Military and Naval Affairs. XII. Philadelphia: L. R. Hamersly & Co.: 177–213. OCLC 228667393.
• Brassey, Thomas A. (1893). "Chapter IV: Relative Strength". The Naval Annual. Portsmouth: J. Griffin & Co.: 66–73. OCLC 496786828.
• Brassey, Thomas A. (1895). "Chapter III: Relative Strength". The Naval Annual. Portsmouth: J. Griffin & Co.: 49–59. OCLC 496786828.
• Brassey, Thomas A. (1896). "Chapter III: Relative Strength". The Naval Annual. Portsmouth: J. Griffin & Co.: 61–71. OCLC 496786828.
• Brassey, Thomas A. (1897). "Chapter III: Relative Strength". The Naval Annual. Portsmouth: J. Griffin & Co.: 56–77. OCLC 496786828.
• Brassey, Thomas A. (1908). "Chapter III: Comparative Strength". The Naval Annual. Portsmouth: J. Griffin & Co.: 48–57. OCLC 496786828.
• Campbell, N. J. M. (1979). "France". In Gardiner, Robert (ed.). Conway's All the World's Fighting Ships 1860–1905. London: Conway Maritime Press. pp. 283–333. ISBN 978-0-85177-133-5.
• Dorn, E. J. & Drake, J. C. (July 1894). "Notes on Ships and Torpedo Boats". Notes on the Year's Naval Progress. XIII. Washington, D.C.: United States Office of Naval Intelligence: 3–78. OCLC 727366607.
• Fisher, Edward C., ed. (1969). "157/67 French Protected Cruiser Isly". Warship International. VI (3). Toledo: International Naval Research Organization: 238. ISSN 0043-0374.
• Garbett, H., ed. (May 1901). "Naval Notes: France". Journal of the Royal United Service Institution. XVI (279). London: J. J. Keliher & Co.: 610–614. OCLC 1077860366.
• Garbett, H., ed. (1903). "Naval Notes: France". Journal of the Royal United Service Institution. XLVII (299). London: J. J. Keliher & Co.: 84–89. OCLC 1077860366.
• Garbett, H., ed. (January 1908). "Naval Notes: France". Journal of the Royal United Service Institution. LLI (359). London: J. J. Keliher & Co.: 100–103. OCLC 1077860366.
• Leyland, John (1901). "Chapter IV: Comparative Strength". The Naval Annual. Portsmouth: J. Griffin & Co.: 71–79. OCLC 496786828.
• "Naval Notes: France". Journal of the Royal United Service Institution. XLIII (254). London: J. J. Keliher & Co.: 322–324 April 1899. OCLC 1077860366.
• Roberts, Stephen (2021). French Warships in the Age of Steam 1859–1914. Barnsley: Seaforth. ISBN 978-1-5267-4533-0.
• Ropp, Theodore (1987). Roberts, Stephen S. (ed.). The Development of a Modern Navy: French Naval Policy, 1871–1904. Annapolis: Naval Institute Press. ISBN 978-0-87021-141-6.