HMS Hydra (pennant number A144) was a Royal Navy deep ocean hydrographic survey vessel, the third of the original three of the Hecla class.

In the month after first commissioning Hydra carried out machinery and equipment trials and embarked stores at Chatham, before sailing for surveys in the North Atlantic.

She then visited Copenhagen and for the remainder of 1966, was employed in searching for wrecks in the shipping lanes of the North Sea and the approaches to the Dover Strait, before returning to Chatham in early December for her winter lie-up.

March 1967 saw the ship carrying out a short survey of the critical depths at the entrance of the Black Deep Channel in the Thames estuary.

She then carried out a major survey of the bathymetry, gravity anomalies and total magnetic field in a large area of the Atlantic Ocean, covering the North-West Approaches to Britain.

At Gibraltar in mid-November, she conducted trials of towed and free balloons carrying meteorological instruments before reaching Chatham for refit on 24 November 1967.

The ship sailed Chatham in late October and carried out surveys off the west coast of Africa, spending Christmas 1968 in Gibraltar.

However, she was detached after a fortnight to support the British task force sent from Singapore to relieve the area of East Pakistan stricken by a severe cyclone and storm surge.

The surveys of the Malacca Strait were concluded in March 1971 and she then spent three weeks in Hong Kong charting waters to the south of Lantao.

She called at Yokosuka, Long Beach, Acapulco and Bridgetown, Barbados, making gravity, magnetics and bathymetric observations on passage and investigating several shoals.

She sailed from Hong Kong on 28 October and arrived in Singapore for her annual refit which began on 13 November; the most important work was the installation of the SRN9 satellite navigation system.

Preparations for future surveys were carried out around Fiji in late 1973 and a visit was made to Sydney on passage back to Singapore, where she arrived on 26 October for refit; the ship's company lived ashore in the ANZUK barracks.

Survey was made of Epi Island, and other areas, of the New Hebrides on passage for Auckland, New Zealand, where the ship arrived on 28 November for maintenance and leave.

The main survey was on the traffic separation routes about 60 miles (97 km) from the eastern end of the Persian Gulf, around the Tunb Islands off Iran.

The ship remained in the area until the end of April, working mostly out of Bandar Abbas, but visits were paid to Karachi (for maintenance), Masirah and Dubai.

The autumn of 1979 was spent off the west coast of Scotland, starting a detailed survey of the Western Approaches to the North Channel, an area where a large number of U-boats were sunk in 1946 after their surrender.

Using copies of a recent survey, by sister ship HMS Hecla flown to Dakar from the United Kingdom Hydrographic Office, in Taunton, HMS Hydra's two surveying motor boats began sounding and sonar sweeping and located the ditched machine, the local port authority marking the helicopter's position with a float.

She arrived in Lagos, Nigeria, on 5 October 1981, in company with the destroyer USS Conyngham [7][verification needed]), which she had met, by chance, in fog outside the entrance to the port.

Leaving a handful of volunteers to guard the various sites on island shores, she sailed north in order to spend two weeks alongside in St. Petersburg, Florida,[14] arriving 18 December, for Christmas and New Year 1981/1982.

Hydrographic surveys continued in the BVI, including a detached boat camp in West Anegada,[15] until completion on 8 February, anchoring that night in Cane Garden Bay, Tortola.

HMS Hydra was converted in Portsmouth Naval Base for service as a hospital ship – a replenishment at sea position was fitted, the yellow funnel painted white and red crosses painted prominently, and the starboard engine replaced – and she sailed on 24 April 1982, in company with her sister-ship HMS Herald,[17] with additional medical staff, for the South Atlantic.

A rendezvous was made on 25 May 1982 with the requisitioned P&O liner, the troopship SS Canberra, and MV Norland in order to transfer casualties by the ship's Westland Wasp helicopter.

Underway the next day, 2 June 1982, on passage for Montevideo, she undertook the ship's first-ever replenishment at sea – an RAS(L) – with the oiler RFA Olmeda, in order to take on fuel.

The ship arrived in the River Plate on 6 June, disembarking her patients in the full glare of the world's media, eager for news and photographs.

After the surrender, to Royal Marines Major-General Jeremy Moore, of the Argentine occupying forces on 14 June 1982, HMS Hydra stayed behind as the Falkland Islands Hospital Ship, based in Stanley (see [22]), until the airport runway was repaired and extended.

She finally left Stanley on 27 August 1982, calling at Ascension Island on 9 September 1982, disembarking an advance leave party to fly home ahead of the ship.

HMS Hydra was the last unit of the original Operation Corporate Task Force to return to the UK, arriving to an extraordinary welcome in Portsmouth on 24 September 1982; the Hydrographer of the Navy, Rear-Admiral David Haslam, embarked for the passage from Spithead, his flag flying from the ship's HiFix mast so as not to displace the Red Cross flag from the mainmast; also notable was the salute paid to HMS Hydra by the NATO Commander, COMSTRIKFLTLANT, Vice-Admiral James A Lyons Jr of the United States Navy, and the ship's company of his flagship, USS Mount Whitney,[24] lining the deck.

In early September 1983, HMS Hydra returned to Scottish waters and began surveys to the west of the Outer Hebrides for a proposed deep draught shipping route.

A visit was made to Haifa and then the ship called at Gibraltar before conducting a short examination of the Chaucer Bank before returning to Devonport in mid-April 1984.

The remainder of 1984 was spent surveying between St Kilda and Barra, off the west coast of Scotland, with a short period on oceanographic work in northern waters.