The I-class ships were improved versions of the preceding H-class. They displaced 1,370 long tons (1,390 t) at standard load and 1,888 long tons (1,918 t) at deep load. The ships had an overall length of 323 feet (98.5 m), a beam of 33 feet (10.1 m) and a draught of 12 feet 6 inches (3.8 m). They were powered by two Parsons geared steam turbines, each driving one propeller shaft, using steam provided by three Admiralty three-drum boilers. The turbines developed a total of 34,000 shaft horsepower (25,000 kW) and were intended to give a maximum speed of 35.5 knots (65.7 km/h; 40.9 mph).[1]Isis reached a speed of 35.3 knots (65.4 km/h; 40.6 mph) from 33,849 shp (25,241 kW) during her sea trials.[2] The ships carried enough fuel oil to give them a range of 5,500 nautical miles (10,200 km; 6,300 mi) at 15 knots (28 km/h; 17 mph). Their crew numbered 145 officers and ratings.[1]
The ships mounted four 4.7-inch (120 mm) Mark IX guns in single mounts, designated 'A', 'B', 'X' and 'Y' from bow to stern. For anti-aircraft (AA) defence, they had two quadruple mounts for the 0.5 inch Vickers Mark IIImachine gun. The I class was fitted with two above-water quintuple torpedo tube mounts amidships for 21-inch (533 mm) torpedoes.[3] One depth charge rack and two throwers were fitted; 16 depth charges were originally carried,[1] but this increased to 35 shortly after the war began.[4] The I-class ships were fitted with the ASDIC sound detection system to locate submarines underwater.[5]
Isis was hit in 1941 off Beirut, Lebanon after the Battle of Crete. She pursued two Vichy French destroyers which escaped. A Junkers Ju 88 aircraft then attacked and severely damaged her. Hero attempted to tow her to Haifa, Palestine. The tow rope snapped, however the engines were restarted and she successfully reached Haifa.
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Friedman, Norman (2006). British Destroyers & Frigates: The Second World War and After. Annapolis, Maryland: Naval Institute Press. ISBN1-86176-137-6.
Hodges, Peter & Friedman, Norman (1979). Destroyer Weapons of World War 2. Greenwich: Conway Maritime Press. ISBN978-0-85177-137-3.
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March, Edgar J. (1966). British Destroyers: A History of Development, 1892-1953; Drawn by Admiralty Permission From Official Records & Returns, Ships' Covers & Building Plans. London: Seeley Service. OCLC164893555.
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Whitley, M. J. (1988). Destroyers of World War Two: An International Encyclopedia. Annapolis, Maryland: Naval Institute Press. ISBN0-87021-326-1.