HMS G9 was a British G class submarine, one of eight Royal Navy submarines known to have been lost to friendly fire in World War I. Construction The second of her class built by Vickers at Barrow-in-Furness, G9 was laid down on 8 December 1914. She was launched on 15 June 1916, and commissioned on 22 August that year. Description The G-class submarines were designed by the Admiralty in response to a rumour that the Germans were building double-hulled submarines for overseas duties. The submarines had a length of overall, a beam of and a mean draft of . They displaced on the surface and submerged. The G-class submarines had a crew of 30 officers and ratings. They had a partial double hull. For surface running, the boats were powered by two Vickers two-stroke diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a electric motor. They could reach on the surface and underwater. On the surface, the G class had a range of at . The boats were intended to be armed with one 21-inch (53.3 cm) torpedo tube in the bow and two 18-inch (45 cm) torpedo tubes on the beam. This was revised, however, while they were under construction, the 21-inch tube was moved to the stern and two additional 18-inch tubes were added in the bow. They carried two 21-inch and eight 18-inch torpedoes. The G-class submarines were also armed with a single deck gun. War service The role of the G class was to patrol the North Sea and German Bight in search of U-boats. Loss G9 was sunk by the destroyer in foul weather on the night of 16 September 1917. G9 had mistaken Pasley for a U-boat and fired two torpedoes at her. The first struck Pasley on her starboard quarter, but too acutely to detonate; the second passed astern. On seeing the submarine's wash, Pasleys officer of the watch, Midshipman Frank Wallis, RNR, turned the boat hard to starboard and rammed G9 just aft of amidships all but cutting her in two, and she sank less than one minute later with the loss of all but one of her crew, Stoker William Drake. Commanded by Lieutenant Commander The Hon. Byron Plantagenet Cary, Bt., G9 had sailed Scapa Flow on 9 September 1917 to patrol an area between Shetland and Norway. On 15 September 1917, she was ordered