Imperial fortress

described Malta, Gibraltar, Bermuda, and Halifax as Imperial fortresses at the 1887 Colonial Conference, though by that point they had been so designated for decades. Later historians have also given the title "imperial fortress" to St. Helena and Mauritius, despite their lacking naval dockyards and not serving as home bases for station naval squadrons.
The fortresses provided safe harbours; coal stores; and dockyards to protect and supply Royal Navy warships. They had numbers of soldiers sufficient not only for local defence, but also to provide expeditionary forces to work with the Royal Navy, as well as stockpiles of military supplies.

History

Although the War Office took over from local officials the funding and operational control of auxiliary forces in the British Isles from 1871 onwards, the trend of Imperial defence policy during the course of the 19th century was to remove regular units of the British Army from colonial garrison duty wherever strategic concerns did not require their retention, with local governments expected to organise and fund auxiliary forces for local defence. The main exceptions were the four Imperial fortresses, which the regular army continued to garrison, and within which the part-time militia and volunteer units were funded as parts of the British Army and brigaded with regular units. The 1887 Colonial Conference sat in London from April 4 until May 9, 1887. At the conference, it was asserted that:
Halifax and Bermuda controlled the transatlantic sea lanes between North America and Europe, and were placed to dominate the Atlantic seaboard of the United States, as well as to control the western Atlantic Ocean from the Arctic to the West Indies. In 1828, Royal Navy Purser Richard Cotter wrote of Bermuda:
Gibraltar controlled passage between the Atlantic Ocean and the Mediterranean Sea, and Malta, aside from supporting operations in the Mediterranean and Black Sea, served as a base for naval and military forces that would be able to deploy relatively quickly to the Indian and Pacific Oceans once the Suez Canal was completed in 1869.
Halifax ceased to be an Imperial fortress in stages. With the 1867 confederation of the Dominion of Canada, military defence of Canada would be transferred to the militia of the dominion government, and the British Army withdrew most of its establishment from the continent, leaving small military garrisons to defend the Royal Naval Dockyard at Halifax, Nova Scotia and the Esquimalt Royal Navy Dockyard in British Columbia. These garrisons were withdrawn along with the Royal Navy establishments when the two Canadian dockyards were closed in 1905, then sold to the government of the dominion.
File:America and West Indies Station 1st Division off Admiralty House Bermuda in 1931.jpg|thumb|America and West Indies Station 1st Division off Admiralty House in 1931 as they depart their base at the Royal Naval Dockyard in Bermuda to exercise on the open North Atlantic
When the Panama Canal opened in 1914, Britain was able to rely on amity and common interests between herself and the United States during and after the First World War, to use Bermuda also as a base from which cruisers could patrol the Pacific coasts of North, Central, and South America. The perception that the only navies that could threaten British control of the sealanes or territory around the globe were all those of countries on the Atlantic or its connected seas had meant Imperial fortresses were only established in this region. This was despite the growth of the Pacific Ocean fleets of Russia and the United States of America during the 19th Century.
Finally the rising power and increasing belligerence of the Japanese empire after the First World War would result in the construction of the Singapore Naval Base, which was completed in 1938, less than four years before hostilities with Japan commenced during the Second World War.
The need to protect these bases of operation, as well as to prevent, via their captures, their becoming bases of similar utility to an enemy, each was heavily defended, making fortress an apt designation. "Fortress" was often included when giving the names of these colonies, e.g. "Fortress Bermuda". Bermuda, protected by an almost impassable barrier reef and unconnected to any continent, required the least defences, but was heavily garrisoned and armed with coastal artillery batteries. Defence of Bermuda, and of the region, was greatly weakened by the economic austerity that followed the conclusion of the Napoleonic Wars and the American War of 1812, which resulted in drastic reductions to the regular forces and to Reserve Forces in the British Isles, and in Bermuda, being allowed to lapse. Bermuda's garrison would slowly increase, with the threat of invasion by the United States during and after the American Civil War resulting in further strengthening of the defences. Bermuda's importance to Imperial defence was only increasing, however.
Halifax was much more vulnerable to attack than Bermuda, which might come over land or water from the United States, Gibraltar was vulnerable to overland attack by Spain and by Napoleonic France, and both Gibraltar and Malta were much more vulnerable to the navies of the Mediterranean, and were even more heavily defended.

Naval and military establishments of the imperial fortresses

Bermuda

North America and West Indies Station Royal Navy establishment in Bermuda
*Admiralty House, Bermuda
**Rose Hill, St. George's Parish
**Mount Wyndham, Hamilton Parish
**St. John's Hill, Pembroke Parish
*Royal Naval Dockyard Bermuda, and the history of the Royal Navy in Bermuda 1795–1995.
**Convict Bay
**Admiralty Island
**Daniel's Head wireless station
**Royal Naval Air Station Bermuda
**Corps of Colonial Marines. 1814–1816.
**Bermuda Sea Cadet Corps
Established by Canadian naval forces
*HMCS Somers Isles 1944–1945
*NRS Bermuda
North America Command
Nova Scotia Command
Bermuda Garrison. 1701–1957.
*St. George's Garrison
**Ordnance Island
**Royal Army Service Corps Wharf
**St. George's Armoury
**East Coast Forts
***Fort St. Catherine's
***Fort Victoria
***Fort Albert
***Western Redoubt
***Fort George
***Town Cut Battery
***Alexandra Battery
***Fort Cunningham
***Fort Popple
***Paget Fort
***Smith's Fort
***Peniston's Redoubt
***St. David's Battery
**Castle Islands Fortifications
***Devonshire Redoubt
***Landward Fort
***King's Castle
***Southampton Fort
***Charles' Fort
***Martello Tower
***Burnt Point Fort
***Ferry Island Fort
*Prospect Camp
**Warwick Camp
**Agar's Island
**Royal Army Service Corps Wharf
**Hamilton Armoury
**Prospect Hill Position
***Fort Prospect
***Fort Langton
***Fort Hamilton
**South Shore Batteries
***Fort Bruere
***Bailey's Bay Battery
***Newton's Bay Fort
***Albouy's Fort
***Harris' Bay Fort
***Sears' Fort
***Devonshire Bay Fort
***Hungry Bay Fort
***Crow Lane Fort
***Middleton's Bay Fort
***West Elbow Bay Fort
***Warwick Camp Battery
***Warwick Fort
***Jobson's Cove Fort
***Great Turtle Bay Battery
***Jobson's Fort
***Hunt's Fort
***Ingham's Fort
***Church Bay Fort East
***Church Bay Fort West
*Boaz Island and Watford Island
**Somerset Armoury
**Whale Bay Battery
**Whale Bay Fort
**West Side Fort
**Wreck Hill Fort
**Scaur Hill Fort
**Daniel's Island Fort and Daniel's Head
**Mangrove Bay Fort
**King's Point Redoubt
**Maria's Hill Fort
Bermuda Militia. 1612–1815.
Bermudian Militia, Volunteer and Territorial Army Units, 1895–1965
Bermuda Militia Artillery
Bermuda Volunteer Rifle Corps
Bermuda Volunteer Engineers
Bermuda Militia Infantry
Royal Bermuda Regiment
Bermuda Home Guard
Bermuda Cadet Corps
Royal Air Force, RAF Darrell's Island. 1939–1945.
Royal Air Force Transport Command station, Kindley Field
Halifax, Nova Scotia
Admiralty House, Halifax
Royal Naval Dockyard, Halifax
Halifax Defence Complex
*Citadel Hill
*Fort Charlotte
*York Redoubt
*Prince of Wales Tower
*Connaught Battery
*Practice Battery
*Sandwich Point
*Camperdown Signal Station
*Fort Chebucto
*Fort Charlotte on George's Island
*Fort Clarence
*Devil's Battery
*Five forts on McNabs Island:
**Fort Ives
**Fort Hugonin
**Sherbrooke Tower
**Strawberry Hill
**Fort McNab
5th Battalion, Royal Garrison Regiment
Gibraltar
British Forces Gibraltar
Royal Navy Dockyard, Gibraltar
Her Majesty's Naval Base Gibraltar
HMS Rooke
Fortifications of Gibraltar
*Alexandra Battery
*Civil Hospital Battery
*Cumberland Flank Battery
*Eliott's Battery
*Europa Advance Batteries
*Europa Battery
*Europa Pass Battery
*Gardiner's Battery
*Genista Battery
*Half Way Battery
*Harding's Battery
*Jones' Battery
*King's Bastion
*Lady Augusta's Battery
*Lady Louisa's Battery
*Lighthouse Battery
*New Mole Battery
*O'Hara's Battery
*Orange Bastion
*Parson's Lodge Battery
*Prince Albert's Front
*Prince of Wales Battery
*Raglan's Battery
*Rock Gun Battery
*Signal Hill Battery
*Victoria Battery
*Wellington Front
*Windmill Hill Batteries
*Woodford's Battery
*Zoca Flank Battery
Devil's Tower Camp
Retrenched Barracks
RAF Gibraltar
Royal Gibraltar Regiment
2nd Battalion, Royal Garrison Regiment
Gibraltar Defence Police
Gibraltar Cadet Force
2 Overseas Squadron, Air Training Corps
Malta
Lascaris War Rooms
Admiralty House, Valletta
Royal Naval Dockyard, Malta
HMS Egmont or HMS St Angelo
HMS Phoenicia
HMS Euroclydon
Royal Navy Hospital Mtarfa
Malta Command
Fortifications of Malta
*Fortifications of Mdina
*Cambridge Battery
*Cittadella
*Della Grazie Battery
*Fort Benghisa
*Fort Chambray
*Fort Campbell
*Fort Delimara
*Fort Leonardo
*Fort Mellieħa
*Fort Ricasoli
*Fort Rinella
*Fort St. Angelo
*Fort Saint Elmo
*Fort Saint Michael
*Fort Saint Rocco
*Fort San Lucian
*Fort San Salvatore
*Fort Tas-Silġ
*Fort Tigné
*Fort Pembroke
*Fort Verdala
*Garden Battery
*Għargħar Battery
*Lascaris Battery
*Pembroke Battery
*Saint Mary's Tower
*Saint Paul's Battery
*Sliema Point Battery
*Spinola Battery
*Tarġa Battery
*Victoria Lines
**Fort Binġemma
**Fort Madalena
**Fort Mosta
*Wolseley Battery
*Żonqor Battery
Pembroke Army Garrison
Malta Tanks
Royal Malta Artillery
Malta Fortress Squadron, Royal Engineers
Royal Signals in Malta
The King's Own Malta Regiment
1st, 3rd, and 4th Battalions, Royal Garrison Regiment
Royal Malta Fencible Regiment
Air Headquarters Malta
RAF Hal Far
RAF Luqa
RAF Ta Kali