Since the 1960s we've been in the 'post battleship era', with the aircraft carrier the chief show of naval power. This is largely because it's been assumed that merchant ships have the right to access the seas where they please in the name of trade. The battleships and the merchant navy are therefore nearly redundant: their chief use was to protect merchant ships so they could have free and unfettered access to the seas in the name of trade.
The British Empire is the purest notion of battleship merchantmen protection, and we need to look again at what we can learn from it. The reality of British Empire was an English governed trade system built around sea routes going in and out of five main hubs.
- Hong Kong - gateway to China and the populous east
- Singapore - gateway to the Pacific and trade routes to North Africa
- Bristol / Liverpool - gateway to the Atlantic and British trade routes to North America
- Cape Town and the routes around the bottom of Africa
- Gibraltar and access to the Med and Suez Canal and to an extent the Atlantic
Please don't think I'm belittling the massive issues which came with the Empire. The destruction of people, culture and governance should not be underestimated, and the misery we exported is sickening. But misery was not the agenda (that was trade): it was the unfortunate byproduct.
After the second world war, the Americans essentially did the job of 'Empire' through bilateral treaties and pan regional/global alliances. This was the genius of Roosevelt and Truman. The protection of global free trade, largely transacted through the US dollar, has been the dominant US foreign affairs agenda for the last 70 years from the WTO through to NATO. If things get really out of hand, the US can still pack an amazingly aggressive military punch, but they don't have to 'own' countries to pack it, they just need allies and aircraft carriers so they can deliver it.
And this is why we should fear Trump. Of course, his views on immigration don't appeal to liberal Brits, but leave that for the citizens of the USA and their grown up democratic system. The issue we should worry about is Trump's ripping up the world's unwritten free trade constitution, which has been building up since 1945 and largely been a force for good. Trump destroying US strategic partnerships and its ally network around the western world could destroy global free trade and make China the predominant power creating a new age of empire, controlled by Beijing.
If this happens there will be a race for resources and markets (it's already happening). The winner will be whoever defends the strategic ports to enable trade and support supply routes last seen when Britannia ruled the waves. And the Chinese are already ahead in the race.