Spanish Armada, fleet assembled and dispatched by King Philip II of Spain in an unsuccessful attempt to invade England in 1588. The defeat of the armada was one of the great achievements of Queen Elizabeth I of England and helped bring about the subsequent decline of the Spanish Empire.

The mission of the armada combined political and religious aims. King Philip, leader of Roman Catholic Spain, could not suppress a revolt of his Protestant subjects in the Netherlands. This revolt, which began in 1566, was aided by Protestant England. By 1586 Philip had decided that he would be unable to defeat the Dutch without first mastering England. At the same time, he hoped to resolve the long-standing religious rivalry between England and Spain by dethroning Elizabeth and reconverting England to Catholicism. He therefore evolved a plan to conquer the English.

The scheme called for coordinating a fleet sailing from Spain with an army from the Netherlands for a simultaneous invasion of England. Philip appointed Alonso Pérez de Guzmán, duke of Medina-Sidonia, to lead the force of 130 ships, which transported nearly 30,000 men. The English, aware of the plan, tried to prevent the armada from sailing by attacking it at Cádiz, Spain, in 1587. They succeeded in delaying it for nearly a year.

By July 1588, however, the armada had sailed. It was first sighted off the English coast on July 29, and a larger English fleet, commanded by Lord Charles Howard (later 1st earl of Nottingham), intercepted it near Plymouth. For the next week, Howard, with his faster, smaller, and more maneuverable ships, attacked the Spanish in battles off Plymouth, Portland Bill, and the Isle of Wight. Unable to break the armada's formation, however, the English waited for a chance to strike a decisive blow.

The opportunity came when the armada anchored near Calais, France, hoping to join the troops scheduled to sail from the Netherlands. Howard ordered ships set on fire to be sent against the armada, producing panic that broke the Spanish formation. In the ensuing Battle of Gravelines on August 8, the English defeated the armada. Unable to sail home through the English Channel because of heavy winds, the badly damaged remaining ships were forced to sail north around Scotland and Ireland to return home. Only 67 of the original 130 ships reached Spain, and most of these were in poor condition.

The failure of the armada did not end the war between England and Spain, which lasted until 1604. It did, however, stimulate English nationalism, secure Protestantism as England's state religion, and create the trust in the English navy that for centuries was the first line of the nation's defense. For Spain, in contrast, it was a demoralizing defeat that nearly bankrupted the treasury.