The threat of Nazi invasion has obscured the terrifying threat of Napoleonic invasion in public consciousness. When James Thomson wrote "Rule Britannia" in 1740 and Thomas Arne set it to music, it was not a triumphalist piece. It was a cry for help...
A plea for ships to defend communities from European kings and African slavers, but also a cry for civil liberty, because an island nation with a strong navy should not need a Cromwellian standing army for defence:
"Britons never will be slaves" defies any home-grown tyrant who can turn his army on the populace, unlike "The nations, not so blest as thee, Must, in their turns, to tyrants fall".
We're lucky to be surrounded by the sea. Let's use that!
Over 60 years later the cry had been answered. If Napoleon could bring his vast army, Britain would fall in days. Yet Britain's Royal Navy was the swiftest, most advanced and efficient in the world. Nelson's victory at the Battle of the Nile, and then against the combined French and Spanish fleets at Trafalgar in 1805, meant Napoleon could not invade.
1066. The Battle of Hastings. Britain has not been successfully invaded since. Almost a thousand years.