The S-class submarines were designed to patrol the restricted waters of the North Sea and the Mediterranean Sea. The third batch was slightly enlarged and improved over the preceding second batch of the S-class. The submarines had a length of overall, a beam of and a draught of. They displaced on the surface and submerged. The S-class submarines had a crew of 48 officers and ratings. They had a diving depth of. For surface running, the boats were powered by two 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 third-batch boats had a range of at and at submerged. The boats were armed with seven 21 inch torpedo tubes. A half-dozen of these were in the bow and there was one external tube in the stern. They carried six reload torpedoes for the bow tubes for a total of thirteen torpedoes. Twelve mines could be carried in lieu of the internally stowed torpedoes. They were also armed with a 3-inch deck gun. It is uncertain if Sibyl was completed with a Oerlikon light AA gun or had one added later. The third-batch S-class boats were fitted with either a Type 129AR or 138 ASDIC system and a Type 291 or 291W early-warning radar.
Sibyl had a distinguished career, sinking numerous enemy ships, including the Italian merchant Pegli, the French merchant St. Nazaire, the German auxiliary minesweeper M 7022/Hummer, five Greek sailing vessels and an unknown sailing vessel. She also unsuccessfully attacked the Italian merchant Fabriano, the German tanker Centaur and what is identified as 'a merchant of about 1500 tons' in a German convoy. Her commanding officer between June 1942 and 3 July 1944 was Lt. Ernest John Donaldson Turner, who was awarded the Distinguished Service Order on 23 June 1943. Turner was succeeded as commander by Lt. Huston Roe Murray, who commanded her for the rest of the war. His First Lieutenant was Stephen Jenner, who later became the commander of the Canadian Submarine fleet.
Far East
On being transferred to operate in the Pacific in early 1945, Sibyl continued to cause losses to enemy shipping. The first Far East patrol was spent around the Andaman Islands and south of Singapore in the Malacca Strait. She sank a number of Japanese vessels with gunfire and scuttling charges in the Malacca Straits, and was strafed by aircraft and depth charged three times after these successful attacks. Sibyl was the first British submarine to surface in Singapore harbour after the Japanese surrendered. She operated out of Trincomalee, Ceylon from the depot ship. After the atom bombs were dropped on Japan, Louis Mountbatten, Supreme Commander in the Far East wanted the surrender signed in Singapore and called for the fleet to be there. HMS Sibyl had been in the harbour the longest so her men were invited to the ceremony, which was held aboard. The mainly British and Australian prisoners of war held in Changi jail by the Japanese were released and taken on board the British ships and fed corned beef sandwiches and hot tea, as they were in terrible condition. It was noted that the entire harbour smelled of freshly baked bread for several days as the numerous ship's galleys were put to the task of feeding the starving prisoners of war.
