HMNB Portsmouth (HM Dockyard, Portsmouth)

His Majesty's Naval Base, Portsmouth is one of three Royal Navy operating bases in the United Kingdom, alongside HMNB Clyde and HMNB Devonport. It occupies the eastern shore of Portsmouth Harbour, within the city of Portsmouth, Hampshire, north of the Solent and the Isle of Wight. The site covers some 122 hectares and is owned by the Ministry of Defence through Defence Equipment and Support, with the Royal Navy as operator.

The base is home to the Portsmouth Flotilla and to around two-thirds of the Royal Navy surface fleet. It homeports the Queen Elizabeth-class aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales, the Type 45 destroyers, Hunt-class mine countermeasures vessels, River-class offshore patrol vessels and Archer-class training craft attached to University Royal Naval Units. Cutlass-class patrol boats assigned to the Gibraltar Squadron and River-class vessels forward-deployed to the Falklands and the Indo-Pacific remain administratively part of the flotilla. HMS Stirling Castle, a former Royal Fleet Auxiliary vessel, has operated from Portsmouth since mid-2025 as mothership for the autonomous systems of the Mine Threat and Exploitation Group. The Defence Dive School and Fleet Diving Unit Portsmouth operate Sea-class diving support boats from the base. XV Patrick Blackett, an experimental vessel, has been based there since 2022. HMS Victory, still in commission, lies in No. 2 Dry Dock.

Command is exercised by the Naval Base Commander (Portsmouth), a commodore. The King's Harbour Master is the regulatory authority for the Dockyard Port of Portsmouth, an area of about 50 square miles covering Portsmouth Harbour and the Eastern Solent; harbour control is located in the Semaphore Tower, and ship movements are handled by admiralty pilots under the Chief Admiralty Pilot. The base provides naval logistics, accommodation and messing, personnel support functions, and offices for Navy Command Headquarters staff. Ship repair and maintenance facilities around No. 3 Basin are operated by BAE Systems Maritime Services. Harbour dredging and the strengthening of Victory Jetty and Princess Royal Jetty were completed from 2013 to receive the carriers, which arrived in 2017 and 2019.

Naval use of the site dates from a dock ordered in 1194, and the yard functioned for centuries as HM Dockyard, Portsmouth, a state facility for building, repairing and maintaining warships. The term Naval Base came into use from the 1970s. In 1984 the dockyard function was downgraded to the Fleet Maintenance and Repair Organisation, privatised in 1998. Block construction of warships resumed in 2002–03 and ceased in 2014.