The seventeenth Royal Navy vessel to be named HMS DOLPHIN was the Royal Naval shore establishment sited at Fort Blockhouse in Gosport, the home of the Royal Navy Submarine Service from 1904 to 1999, and location of the Royal Navy Submarine School.

The blockhouse and fortifications of the site had been constructed from the 14th century onwards, but, in the late nineteenth century, it was deemed surplus by the Royal Commission, and was handed over to the Royal Navy in 1904. The navy set about expanding the site by adding new blocks and accommodation, and the base became an independent command in August 1912. Originally it was known simply as Haslar Submarine Base, but was renamed as HMS DOLPHIN sometime after 1907, when the last ship of that name was brought to the site to provide extra accommodation. Heavy bombing during WWII on Gosport and Portsmouth, saw the submarine training school moved to Blyth in Northumberland as HMS ELFIN.

DOLPHIN closed as a submarine base on 30 September 1998, although the last RN submarine permanently based at Gosport was HMS OPOSSUM which had left five years earlier in 1993. The Royal Navy Submarine School (RNSMS) remained at DOLPHIN until 23 December 1999 when it closed prior to relocation to HMS RALEIGH at Torpoint in Cornwall. The Submarine Escape Training Tank (SETT), a 30-metre deep tank of water used to instruct all RN submariners in pressurised escape, remained active at the same site, now renamed Fort Blockhouse, until early 2020, when it was replaced with a newer training facility at HM Naval Base Clyde.

(Source: Wikipedia)