Acheron-class destroyer
The "Acheron" class (officially re-designated as the I class in October 1913) was a class of twenty-three destroyers of the British Royal Navy, all built under the 1910–11 Programme and completed between 1911 and 1912, which served during World War I. A further six ships were built to the same design for the Royal Australian Navy as River-class destroyers. There was considerable variation between the design and construction of ships within this class, which should be considered as more of a post-build grouping than a homogeneous class. Design. Originally, 20 ships, including "Acheron , were ordered, but an additional three were completed by Yarrow & Company. Three River-class destroyers of the Royal Australian Navy were laid down in British yards, with a further three built in Australia. The Acherons" were generally repeats of the preceding "Acorn"- or H-class, although "Acheron" herself and five others were builders' specials. They differed from the "Acorn"s in having only two funnels, both of which were short, the foremost being thicker than the after stack. The 12-pounder guns were mounted slightly further forward than in the "Acorn"s. Variation within the class. Fourteen of the class were completed  to an Admiralty standard design, although those built by John Brown and Company at Clydebank ("Hind", "Hornet" and "Hydra") had Brown-Curtis type turbines and only two shafts. "Archer" and "Attack" used steam at higher pressures and "Badger" and "Beaver" were completed with geared steam turbines for evaluation purposes, achieving speeds of on trials. Thornycroft specials. "Acheron" and "Ariel" were longer (77m), had higher installed power (15,500 shp) and were consequently faster, achieving on trials. Yarrow specials (or "special I class"). Sir Alfred Yarrow maintained that it was possible to build strong, seaworthy destroyers with a speed of , and  eventually a contract for three such boats was placed with the firm. They were a little larger than the rest of the class, and developed , but carried the same armament. Like the John Brown-built boats "Hind", "Hydra" and "Hornet", they had only 2 shafts, with steam developed in 2 Yarrow-type water-tube boilers and delivered to 2 Parsons turbines. "Firedrake", "Lurcher" and "Oak" were distinctive in appearance and indeed much faster. They all exceeded their contract speed, "Lurcher" making over . Conversion to minelayers. "Ferret", "Sandfly" and "Ariel" were converted into fast minelaying destroyers in 1917, serving with the  20th Flotilla. They were each capable of laying 40 mines. Evaluation. This class of torpedo boat destroyers (TBDs, or colloquially, "boats") handled well and were excellent sea boats; like similar classes of TBDs of the time, they had open bridges but were much drier at sea than was the norm.