page_title: HMS Polyphemus (1881)
section_title: Design
hierarchical_section_title: HMS Polyphemus (1881) / Design
caption_attribution_description: Right elevation, deck plan and hull cross-section diagrams of British torpedo ram HMS Polyphemus.
context_page_description: The third HMS Polyphemus was a Royal Navy torpedo ram, serving from 1881 until 1903. A shallow-draft, fast, low-profile vessel, she was designed to penetrate enemy harbours at speed and sink anchored ships. Designed by Nathaniel Barnaby primarily as a protected torpedo boat, the ram was provided very much as secondary armament.
  It has been suggested that H. G. Wells’ fictional HMS Thunder Child from his novel The War of the Worlds may have been based on this ship, in part because he described Thunder Child as an ironclad torpedo ram, and Polyphemus was the only ship of this type which the Royal Navy possessed.
context_section_description: The Admiralty set up the "Torpedo Committee" in 1872 to examine ways in which the newly invented Whitehead torpedo could be launched at sea.  The Royal Navy's first purpose-built torpedo launching ship was HMS Vesuvius, which, with a maximum speed of less than 10 knots,  was intended to stealthily approach within a few hundred yards of enemy ships at night to launch her torpedoes. Leading on from this, Barnaby and his assistant J Dunn, proposed in the mid-1870s a fast cigar-shaped vessel with five submerged torpedo tubes and protected by 2 inches of armour over the deck. The design was modified in late 1875 into a larger vessel equipped with a ram. Early in 1876 the design was modified again into a 240-foot-long (73 m) unarmoured torpedo ram with a top speed of 17 knots. Later the design was modified yet again to have armour added to the exposed steel deck. 
  The ship was equipped with a 250-ton cast iron keel which could be released in an emergency to increase the buoyancy of the hull. It was held in place by two spindles which both had to be turned to release the keel and which were tested fortnightly.
  The ship was equipped with twin boiler and engine rooms, and a low turtle-back hull which was almost submerged when the vessel was travelling at speed, and had a normal bunker capacity of 200 tons of coal, and 300 tons maximum.
caption: The layout of Polyphemus as depicted in Brasseys Naval Annual 1888
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