The San Carlos was a 18th-century Spanish packet boat built in 1765 at the Royal Shipyard of Havana, Cuba. The ship entered service in 1765 with two-decks and 80 guns. In 1775, the San Carlos was the first ship to enter the San Francisco Bay, under the command of Spanish naval officer and explorer, Lieutenant Juan Manuel de Ayala. In 1801, it sailed to Cartagena, Spain and converted into a three-deck ship with 112 guns.