Most people know that Britain was invaded by the Romans, by the Vikings, and by the Normans. Many will know about the Spanish Armada, launched by Philip II in 1588 to bring Protestant England to submission. But fewer people know that Philip launched a second armada in 1596 or that invasion plans were drawn up by the French in 1692, 1708, 1743, 1756, 1759, 1796, and 1801, and by the French together with the Spanish in 1779. In 1719, Spanish troops even landed in Scotland. Charles XII and Peter the Great wished to invade Britain and Napoleon himself wrote that in his imagination he could see the tri-colour fluttering over the Tower of London.

New invasion plans were drawn up by the Germans in 1896 and by the French in 1898, and Britain narrowly avoided invasion by Nazi Germany in WW2. Yet despite the almost permanent threat of invasion by the Spanish in the 16th century, by the French from the 17th to the 19th centuries, and by the Germans in the 20th century, Britain has not been successfully invaded since 1066.

Beginning with the first real invasion attempt of the modern era and one of the decisive naval battles in world history, McLynn takes us through the many invasion plans and attempts and shows us how each one failed due a mixture of incompetent management, clash of egos, unreliable weather, and the strength of British sea power. He concludes with Hitler's failed invasion attempt during WW2 showing how despite all the risks, Hitler was lulled into a false sense of security by the ease with which Germany had managed to defeat France in 1940.

McLynn discusses the different strategies involved for invading Britain by sea and the means by which Britain tried to defend itself using diplomacy, economic warfare, espionage, and pre-emptive strikes. Finally, he shows that after having been threatened with invasion for four centuries, England was itself the springboard from which the greatest invasion fleet of all time was launched.