The original harbour was naturally sheltered by the south coast of England, Chesil Beach and the Isle of Portland, providing refuge for ships against weather in all directions except east.

[5] Prompted by the expansion of the French naval port of Cherbourg, just across the English Channel, the Royal Navy established a base at Portland in 1845; a scheme for the harbour to be transformed into a refuge had been granted parliamentary approval the year before.

[6] Similar harbours of refuge would be built at Alderney, Dover, Holyhead, and later (in response to the increased naval threat from Germany) at Peterhead.

[8] During 1848, HM Prison Portland was established to provide convict labour to quarry the stone needed to construct the breakwaters and the harbour defences.

[4] During the 20th century the harbour increasingly became a naval oiling depot and, beginning in the early 1900s, the tidal creek the Mere began to be filled in for a vast tank farm.

[4] In the 1850s it had been proposed that a full Royal Navy Dockyard be established, with three dry docks, three shipbuilding slips, a fitting-out basin and associated factory facilities.

Under its command, a 'listening school' was established to help develop hydrophone underwater listening devices and other anti-submarine measures, and to train personnel in their use.

The school initially operated from temporary accommodation in Weymouth, before moving in 1918 to a site at East Weare, just south of the Dockyard.

Meanwhile, the experimental work was carried out within the dockyard itself: namely in a pair of sheds on the inner breakwater and in what had been the Admiralty Slaughter Houses (just to the south, at Balaclava Bay), which were swiftly converted into workshops.

[34] (HMS Icewhale initially served as the depot ship,[30] and was duly renamed Osprey; but in 1928 she was sold out of service and the name was transferred ashore).

The second of only two Victoria Crosses awarded for action in the United Kingdom was posthumously bestowed on Jack Foreman Mantle, who died at his post on the ship.

The King, Prime Minister Churchill and Free French leader General de Gaulle came to see the great D-Day preparations at Portland; activity in the harbour was continuous.

After the war, Portland's role in the liberation of Europe was marked by a ceremony in August 1945, when the American Ambassador John G. Winant unveiled a stone in Victoria Gardens commemorating the passing by the spot of 418,585 troops and 144,093 vehicles the previous June.

[6] After the war, in 1946, ten Phoenix caissons of the Mulberry Harbour were towed back to Portland, eight of which were later given to the Netherlands to repair storm breaches in the dykes in 1953.

Over the next few years its headquarters on Balaclava Bay were rebuilt and extended, and it was again renamed as HM Underwater Detection Establishment (HMUDE).

[45] In February 1958 it was announced in Parliament by the First Lord of the Admiralty that Portland Dockyard was to close the following year (though the naval base would be retained).

As planned, Portland's Royal Dockyard closed in 1959, but the Naval Base remained open 'in support of the local establishments and H.M. ships using the harbour'.

[47] In 1984, two large accommodation blocks, totalling £25-30 million, were built in Castletown as barracks for Royal Navy personnel, along with a sports centre.

[6] There was opposition against the closure from the local economy, as well as all ranks of naval personnel, who felt Portland's surrounding coast was perfect for exercising ships.

[53] The harbour was sold off by the Royal Navy in 1996, allowing it to be used both as a centre for water sports and as a service facility for Channel shipping.

Renamed Jascon 27, the ship left Portland under tow in 2010, bound for Nigeria, to be refurbished for use as an oil industry accommodation vessel.

The commercial port has expanded since its initial establishment; the Britannia Passenger Terminal was opened by HRH Prince Philip on 14 July 1999.

However, despite published reports in 1996 revealing that Portland Port Ltd were interested in the renovation of historic coastal fortifications in the area, no restoration of any kind has taken place.

[47] Commercial activities on the water include specialist diving services for vessels and repairs and maintenance, as well as a bunkering (fuelling) station.

The Royal Yachting Association had expressed interest in securing a suitable site locally for a number of decades, in order to make use of the harbour's natural advantages.

This facility was open by Prince Philip, Duke of Edinburgh in April 2009 and is situated directly adjacent to the National Sailing Academy.

At the Breakwater Fort is a World War II 29 millimetre spigot mortar emplacement,[70] a pillbox,[71] and a battery observation post.

[78] On the North Eastern Breakwater, within the centre area, is a World War II coastal battery with coast artillery searchlights.

During World War II, a number of anti-invasion structures were placed at Balaclava Bay, including an anti boat landing obstacle,[89] and a minefield.

[93] As part of the defence for HMS Osprey, now demolished, a "Yarnold Sanger" pillbox is located on Incline Road, constructed during the Cold War.