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 added new blocks and accommodation for various ranks, 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 to be called
HMS Dolphin was brought to the site to provide extra accommodation. Heavy bombing during the
Second World War on Gosport and
Portsmouth, saw the submarine training school moved to
Blyth in
Northumberland as HMS Elfin. HMS
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 RNSMS staff marched into HMS
Raleigh and were welcomed on board by Commodore Lockwood on 31 January 2000. The RNSMS is located in the Dolphin and Astute blocks at
Raleigh, although the
Submarine Escape Training Tank (SETT), a 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. == Submarine museum ==