On this day, the 7th of August 1588, the Invincible Spanish Armada was destroyed by the English fleet off the coast of Gravelines, France. (What is it with naming ships some synonym of "unsinkable", only for them to sink?)
The Spanish Armada was in the process of an invasion of England, under the justification of restoring the Catholic faith to England (but also due to English piracy of Spanish trade in the Caribbean) It consisted of some 130 ships, 40 of these being battle-line ships and the rest for soldier transport and cargo. It is estimated that the Armada had around 8,000 sailors and 19,000 soldiers.
The Armada was defeated not in all out battle, but rather after the English sent, at midnight, several fireships into their anchored formation near Calais. The Armada was forced to cut loose and scatter to avoid catching fire, and thus break formation. At dawn, the English fleet sailed in and sunk or seriously damaged many of the disorganised ships. The Spanish remnants were forced to return home the long way, up around Scotland, and lost many more ships in the process.
The defeat of the Armada effectively saved England (and the Dutch Republic) from land invasion and annexation into the Spanish Empire.