The constant warring with Spain and France meant the Royal Navy went through many structural and strategic changes as their power grew and waned - but mainly grew. In the 1700s Britain was using the restrictive trade technology of Mercantalism which meant many political decisions and confrontations were based on trade. Pitt turned trade on its head stating that it was the oceans, and the Royal Navy's dominance of them that tied Britain's Empire together.

Arthur Herman writes;

[t]The "blue water" strategists did grasp an essential point about British naval power: without it, Britain's overseas trade could not grow. And it was "the vastness and extensiveness of our [Britain's] trade", said a writer as early as 1718, that made Britain "the most considerable of any nation in the world."

Even today 95% of trade is still done by sea. In the 1700s there was no aviation and for a nation like Britain, isolated by the sea and channel, there were no overland routes.

The Spanish Empire, which was the dominant empire before Britain ousted them were also dependent on ocean trade to sustain their empire. Namely the gold and silver coming across the Atlantic from South America. One of the earliest strategies of Britain in their numerous wars with the Spanish was to use piracy and privateering to capture and disrupt those trade routes, essentially acting as a blockade to Spanish trade.

The Royal Navy formalised it far more in their wars with the French where they used supply convoys to keep a blockade on stations. The Germans also tried it in WWI and WWII with the disruptive technology of the submarine. In maritime strategies strangling an opponents trade through a blockade is common.

As member of Parliament in the 1730s William Pitt understood the importance of trade to Britain's future and to Britain's emerging identity as a commercial, as well as religious, Elect Nation. "When trade is at stake," he argued, "it is your last entrenchment; you must defend it or perish."

But as a statesman in the 1750s, Pitt would turn the standard formula of sea-power and trade inside out. Instead of seeing the navy as a weapon for getting and defending overseas empire, he saw overseas empire as a tool for the navy, giving it the bases it needed to defend British mercantile interests and to increase its own global reach.

Prior to the French wars the Royal Navy did not maintain separate fleets, preferring to keep their fleet concentrated and overseas warring or piracy being done by privateers, often with state backing. The constant wars with the French meant that the Royal Navy was big enough, and strategically justified, to start splitting its forces.

The first of these was the Western Squadron which later became the Channel Fleet. Eventually Gibraltar became a base for the Mediterranean fleet which was used to bottle up the French and stop their fleet from exiting into the Atlantic to disrupt trade or participate in an invasion.

I am not sure what to make of Pitt's change in doctrine. Maybe it is when Britain went from trading nation to empire. Australia certainly came about from Pitt's doctrine, apart from being a convenient place to dump convicts, it was intended as a colony to satisfy the Royal Navy's needs in the Pacific. One of the reason for the choice of Norfolk Island was the tall pines which it was thought could be used for ship-building and repair.

The early self-governing colonists in the late 1800s and Billy Hughes saw Australia in Pitt's manner too. Both thought that Australia was the British Empire in the Pacific. WWII proved that illusionary as British power waned, it is doubtful Britian could have done it in the late 1880s anyway. When Queensland raised militia to invade German New Guinea the Colonial Office had a fit, concerned that it would precipitate war in Europe. Australia eventually invade German New Guinea in 1914 after WWI had been declared.

Edwards' continues;

John Oldmixon may have been the first to point out, back in 1708, that what really made Britain great was not trade but its fleets. Trade was merely a way to pay for them. But Pitt saw even deeper and clearer. The old view of seaborne empire, going back to Hawkins [British Admiral] and Phillip II [of Spain], was of a mother country connected to its various colonies by trade routes, a network of long delicate filaments stretching out over vast empty oceans.

Pitt showed that instead of the oceans dividing Britain's empire, they united them. The fact that the seas were all one could enable a powerful navy to consolidate Britain's imperial possessions and divide and distract those of its enemies.

Pitt turned Britain's supposed weakness, its far-flung global trading networks into strategic strength. Viewed in this way, the Royal Navy gave Britain's maritime empire a vibrancy and dynamicism none of its predecessors, ... ever had.

The comparisons between the Pitt Doctrine and American blue water dominance in the late 20th and early 21st century are inevitable. The US is the undisputed master of blue water projection, able to bring massive resources to bear, at high tempo and for indefinite periods. American power is heavily dependent on its blue water Navy and the deployment of its forces around the world. It could be argued that the doctrine of American empire follows Pitt's.

Chalmer's Johnson records the words of Joseph Nye with, "Our [US] forward presence provides for the stability - the oxygen - that has helped provide for East Asian growth." Nye is arguing the US military is the engine which under-pins the freedom of globalisation and ties the world into the US trade economy.

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More Reading on William pitt

• William Pitt
• Royal Navy
• Arthur Herman
• The Pitt Doctrine