The third HMS Polyphemus was a Royal Navy torpedo ram constructed at Chatham Dockyard, laid down on 21 September 1878 and launched on 15 June 1881. She was completed by September 1882 and served until 1903. As a shallow-draft, fast, low-profile vessel, Polyphemus was designed primarily to penetrate enemy harbours at speed and sink anchored ships, employing a combination of torpedoes and ramming tactics. Her construction featured a low turtle-back hull that was nearly submerged at speed, with twin boiler and engine rooms. She was equipped with twin funnels and a bow fitted with a prominent ram, which could be hinged upward for use. The ship's design incorporated a 250-ton cast iron keel that could be released in emergencies to increase buoyancy, held in place by two spindles. Her armament included five submerged 14-inch-diameter torpedo tubes, carrying 18 Mark II torpedoes with a range of 600 yards and a speed of 18 knots. Notably, the central torpedo tube was fitted with a cast steel bow cap and ram, with a hydrodynamically optimized design tested through model trials. Polyphemus’s deck was protected by 3 inches of armour, and her armament was initially six twin-barreled Nordenfelt 25mm guns, later replaced by six single Hotchkiss 3-pounder quick-firing guns. The vessel was also notable for being the first Royal Navy ship fitted with 80-volt electric lighting, introduced in 1882. The ship featured a flying deck housing the bridge and machine guns, designed to float off as two seaworthy rafts if she sank. Her operational history included service with the Mediterranean Fleet and participation in a simulated attack on Berehaven in 1885, testing tactics against potential Russian threats. She successfully evaded torpedoes and smashed through booms during this exercise. Polyphemus served until 1900, after which she was employed as a tender to HMS Defiance at Devonport. Her design and operational role reflected late 19th-century naval innovation, though her influence waned as newer guns rendered her concept less practical by the time she entered service.

This description has been generated using GPT-4.1-NANO based on the Vessel's wikidata information and then modified by ShipIndex.org staff.