Two hundred and fifteen years ago a (relatively) small number of (mostly) men, less than 15,000 of them, changed the world. (There were some women on many British warships ~ serving the men in various ways, helping the surgeon and caring for the ‘powder monkeys’ ~ very young boys who worked in the ship’s magazines.)
Napoleon was rampaging across Europe; but, although he was a tactical genius, he was a strategic nincompoop who failed to understand that a) Britain was his real enemy; and b) Britain was, still, 200+ years after Elizabeth I, pursuing a maritime strategy and that his “continental system” could not prevail against it.
But Bonaparte ordered his fleet to sea, to land troops in Italy, and Lord Nelson was waiting with a slightly smaller but better, by almost every important measure, fleet. The result was that the combined Franco-Spanish force lost 22 of 33 ships (21 captured ~ the British preferred to capture ships and enjoy the ‘prize money’ rather than sink them) and 7,000 sailors killed and wounded and 7,000 more captured. Nelson lost no ships and fewer than 500 of his sailors were killed.
Although he never quite understood it, Napoleon had just lost the Napoleonic Wars. It would take until 1815, Waterloo, to finally put paid to the man, but the strategic issue was settled at Trafalgar on October 21st.