HMS Thetis (N25) was a Group 1 T-class submarine constructed by Cammell Laird in Birkenhead, England, and launched on 29 June 1938. Designed as a Royal Navy attack submarine, she featured the typical characteristics of the T-class, though specific dimensions and armament details are not provided in the source. Her construction was delayed initially due to jammed forward hydroplanes, but she eventually completed trials in Liverpool Bay under Lieutenant Commander Guy Bolus. During her sea trials on 1 June 1939 in Liverpool Bay, Thetis was involved in a tragic accident that led to her sinking. The incident occurred after the inner hatch on a torpedo tube was opened while the outer hatch was also open, resulting in flooding. The test was complicated by a blocked test cock on torpedo tube 5 and confusing indicator arrangements, which contributed to the inner door being opened prematurely. The inrush of water caused Thetis to sink to 150 feet below the surface. Despite efforts to signal distress and initiate rescue, only four men escaped using the aft escape chamber, while 99 others perished in the disaster. The sinking prompted a redesign of torpedo tube safety measures, including the addition of the "Thetis clip," a latch to prevent accidental opening. The vessel was salvaged, repaired, and recommissioned as HMS Thunderbolt in 1940. As Thunderbolt, she served notably in the Atlantic and Mediterranean theaters during World War II. She sank the Italian submarine Capitano Tarantini in December 1940 and participated in covert operations involving manned torpedoes, including attacks on Axis shipping in Cagliari, Palermo, and Tripoli harbors. Thunderbolt was ultimately lost with all hands on 14 March 1943 off Sicily, attacked by the Italian corvette Cicogna in 1,350 meters of water. Her service history underscores her transition from a tragic accident to an active wartime submarine, contributing to Allied naval efforts before her loss. The disaster had a profound impact on submarine safety procedures and remains a significant event in maritime history.

This description has been generated using GPT-4.1-NANO based on the Vessel's wikidata information and then modified by ShipIndex.org staff.