Philip decided he must get rid of Elizabeth, and return England to a Catholic country. He planned to put his daughter Isabella on the throne, under his control.
So Philip started preparing for the invasion. He started as early as 1584. His first choice as commander was the Marquis of Santa Cruz, but when Santa Cruz died, Philip ordered the Duke of Medina Sedonia to take command of the fleet. The Duke was an experienced warrior and general. On land. He had no naval experience, and, even worse, he
suffered from seasickness. He begged Philip to be dismissed, but Philip ignored the request, and so the duke had no choice but to lead the armada.
Despite Spanish precautions, the English were well aware of the Spanish preparations. In a bold move that was apparently against Elizabeth's wishes, Sir Francis Drake sailed a small English fleet to Cadiz, where they surprised a large number of Spanish warships in the harbour. Drake burned and sunk a number of ships and slipped away before the Spanish could rally. Although the blow at Cadiz was more an annoyance than a major setback, the English took heart from this "singeing of the King of Spain's beard".
By May of 1588, however, the Armada was finally ready to sail. The fleet numbered over 130 ships, making it by far the greatest naval fleet of its age. According to Spanish records, 30,493 men sailed with the Armada, the vast majority of them soldiers. A closer look, however, reveals that this "Invincible Armada" was not quite as well armed as it might seem.
Many of the Spanish vessels were converted merchant ships, better suited to carrying cargo than engaging in warfare at sea. They were broad and heavy, and could not maneuver quickly under sail.
This might not at first glance have seemed a problem to the Spanish. They did not intend to engage the English in a sea battle. The ships of the Armada were only supposed to be troop transport. Their major task was simply to carry armed men to England an unload them for the invasion.
Yet another problem was, because of the loss of ships from drakes attack at Cadiz, new ships had to be built, with new barrels for food, with new wood. The wood had not been dried, and so made the contents of the barrels damp, making the food go rotten and mouldy quicker, so the armada had to stop off at Calais to restock on supplies. This gave the English more time to prepare. Then, the weather turned bad, and forced the ships to turn back. After such a trip, there were many losses, and only 53 out of the original 130 made it back to spain, and many were unfit to ever be put out to sea again.
There are many reasons why the Spanish Armada failed to invade England in 1588. Just two of these were: poor tactical planning by Philip, and bad weather. I think that the most important reason was the fact the Philip did not think about how he could execute the attack successfully as much as he should have done, and so it was a failiure.