In 1667 diplomatic relations between the kingdoms of England and Spain were worsening, and rumours began to circulate in Jamaica about a possible Spanish invasion. Modyford authorised privateers to take action against the Spanish, and issued a letter of marque to Morgan "to draw together the English privateers and take prisoners of the Spanish nation, whereby he might inform of the intention of that enemy to attack Jamaica, of which I have frequent and strong advice". He was given the rank of admiral and, in January 1668, assembled 10 ships and 500 men for the task; he was subsequently joined by 2 more ships and 200 men from Tortuga (now part of Haiti).