Three handwritten letters from 1554 reveal the early-modern Spanish Empire’s maritime economic system. Iberians and Ottomans defended commercial interests in naval battles for Aden, Masqat, Hormuz, and Goa. These letters provide incidental information for a social history of seafaring: tribes’ names (nautaques), coastal uprisings, forced acculturation, unpaid soldiers, viceroy noncompliance, ship locations, winter ports, wind/tide patterns, naval officers, vessel types, military weaponry, enemy-ship capture tactics, colonists’ dietary habits. I focus on references to social entities as components of the maritime economic system that expanded Asian silk trade through Suez, displaced established Spanish silk producers (Moriscos), and spread the silk-raising industry to Mexico. Synchronic analysis shows Suez and silk as parts of Spanish maritime economics Spanish silk workers’ displacement is connected to Asian silk trade and its expansion Tordesillas (1494) revised illustrates Spanish presence in Indian Ocean commerce Letters stress social diversity in maritime activity and encourage archival research