There have many types of shipwrecks but the ones that we will deal with here are from the Spanish Treasure Fleet. There are 2 major Spanish treasure fleet shipwrecks, the 1715 Spanish Treasure Fleet and the 1622 Spanish Treasure Fleet.
Beginning in the 16th century, the Spanish treasure fleets (or West Indies Fleet from Spanish Flota de Indias) transported various metal resources and agricultural goods, including silver, gold, gems, spices, tobacco, silk, and other exotic goods, from the Spanish colonies to Spain. The Crown of Spain took a fifth of the wares and precious metals of private merchants, a tax known as the quinto real.
The treasure fleets consisted of two convoys: the Spanish Caribbean fleet or Flota de Indias, which sailed from a network of ports including Havana, Veracruz, Portobelo and Cartagena to Spain, and the Manila Galleons or Galeón de Manila which linked the Philippines to Acapulco in Mexico. From Acapulco, the Asian goods were transhipped to Veracruz to join the Caribbean treasure fleet, for shipment to Spain.
Spanish ships had brought treasure from the New World since Christopher Columbus’ first expedition of 1492, but a system of convoys started to be developed in the 1520s in response to attacks by privateers. Under this system, two fleets sailed each year from Seville (Cádiz from 1707), consisting of galleons, heavily armed with cannons, and merchant carracks, carrying manufactured goods (and later occasionally slaves). One fleet sailed to the Caribbean, the other to the South American ports of Cartagena, Nombre de Dios (and later Porto Bello); after completing their trade the fleets rendezvoused at Havana in Cuba for the return trip.
Spain strictly controlled this trade through the Casa de Contratación based in Seville. By law, the colonies could only trade with the one designated port in the mother country. Maritime archaeology has shown that the quantity of metals really transported was usually much higher than that recorded at the Archivo General de Indias, as Spanish merchants and Spaniards acting as fronts (cargadores) for foreign merchants resorted to contraband to transport their riches untaxed.
View of Seville in the 16th century
This monopsony lasted for over two centuries, in which Spain first became the richest country in Europe and used this wealth to fight numerous wars in the 16th, 17th and 18th centuries against the Ottoman Empire and most of the major European powers (except the Holy Roman Empire). However, due to inflation in the 17th century, the flow of precious metals from the Indies gradually damaged the Spanish economy.
This economic importance also declined with the drop of production of the American precious metals mines, such as Potosí. The fleets which numbered just 17 ships in 1550 had reached just over 50 much larger vessels by the end of the century. In the middle of the next century, that number had dwindled to around half of its peak and continued to shrink. However, the fleet began to expand again as trade gradually recovered from the last decades of the 17th century.
The Spanish trade of goods and precious metals was continually threatened until the mid 18th century, as Spain’s colonial rivals seized bases or established their own along the Spanish Main and the Spanish West Indies: the English acquired St Kitts in 1624, the French Saint-Domingue in 1625 and the Dutch Curaçao in 1634. In 1739, Admiral Edward Vernon raided Porto Bello (which proved a mere irritant), and in 1762, the British occupied Havana and Manila, forcing changes to the usual pattern of fleet operations.
Charles III began loosening the system in 1765, and in the 1780s Spain opened its colonies to free trade. In 1790, the Casa de Contratación was abolished. The last regular treasure fleet sailed that year. Thereafter small groups of navy frigates would be assigned to the transfer of bullion as required.
Despite the general perception that many Spanish galleons were captured by English or Dutch pirates or privateers, the fact is that very few fleets were actually lost to enemies in the course of flota’s long career. Treasure fleets were captured by Piet Hein in 1628 and destroyed in 1656 and 1657 by Robert Blake. The 1702 treasure fleet was also destroyed in the Battle of Vigo Bay when surprised at port, but had already unloaded most of its silver. In the case of the Manila galleons, only four were ever captured. These losses and those due to hurricanes were heavy economic blows when they occurred, but overall the treasure fleets must be counted as among the most successful naval operations in history.
Wrecks of Spanish treasure ships, whether sunk in naval combat or by storms (those of 1622, 1715 and 1733 being among the worst), are naturally a prime target for modern treasure hunters, and many have been salvaged, like the Nuestra Señora de Atocha.
The following are a few books that are recommended for great information on Treasure Shipwrecks. Go through the link to read about the particular book.