Imperial fortress

Imperial fortress was the designation given in the British Empire to four colonies that were located in strategic positions from each of which Royal Navy squadrons could control the surrounding regions and, between them, much of the planet.
History.
The Imperial fortresses provided not only safe harbours and (with the advent of steam propulsion) coal stores within the area of operation, but also Royal Naval Dockyards where ships of the squadrons could be repaired or maintained without requiring their return to a dockyard in the British Isles.
The Imperial fortresses were also locations where military stores were stockpiled and numbers of soldiers sufficient not only for local defence, but also to provide expeditionary forces to work with the Royal Navy in amphibious campaigns and raids on coasts throughout the regions, could be garrisoned.
These Imperial fortresses originally included:
They were the lynch pins in Britain's domination of the oceans and the Mediterranean and Caribbean seas, including its ability to deny safe passage to enemy naval and merchant vessels while protecting its own merchant trade, as well as to its projection of superior naval and military force anywhere on the planet.
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 demonstrated during the American War of 1812 when the squadron of the Royal Navy's North America Station maintained a blockade of the Atlantic coast of the United States and launched the Chesapeake Campaign from Bermuda, defeating American forces in the Battle of Bladensburg, capturing and burning Washington, DC, and raiding Alexandria, Virginia), as well as to control the western Atlantic Ocean from the Arctic to the West Indies (in the twentieth century, the Bermuda-controlled North America and West Indies Station of the Royal Navy would become the 'America and West Indies Station', its area growing to include the western South Atlantic and the Atlantic coast of South America, as well the Pacific coast from Tierra del Fuego to the Arctic). 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.
The lack of such an Imperial fortress in the region of Asia, the Indian Ocean and the Pacific Ocean was always to be a weakness throughout the nineteenth century (the British Government, ever unwilling to increase, or even maintain, its defence expenditure, relied on there being few nations outside of the Atlantic and its connected seas that possessed fleets capable of threatening British trade or territories, though the nascent United States of America were multiplying towards the Pacific coast of North America, and the Russian Empire and Japanese Empire both had ports on the Pacific and were keen to build large, modern fleets).
As Britain had no base comparable to an Imperial fortress in East Africa, Mauritius, India, Ceylon, Malaysia, Hong Kong, British Columbia or Australasia, after the 1869 completion of the Suez Canal Britain relied on Malta in the Mediterranean Sea to project power over this vast expanse. 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 also use Bermuda, from which cruisers could patrol the Pacific coasts of North, Central, and South America. 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 (Militia, Volunteer Force, and Fencibles), and in Bermuda (Militia and volunteer artillery), 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, and the parlous state of its own defence was commented upon by Sir Henry Hardinge in the House of Commons on the 22 March 1839:
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 (which remains anxious to recover it) and by Napoleonic France, and both Gibraltar and Malta were much more vulnerable to the navies of the Mediterranean (notably those of Spain, France, Italy, and the Ottoman Empire), and were even more heavily defended.