With his convoy safely at anchor in Macau and the China Fleet several weeks from sailing , Cooke decided to reconnoitre Manila and make observations on the port and the Spanish squadron based there . As an added motivation , rumours in Macau suggested that the annual Manila galleon was due to arrive . This ship brought up to two million Spanish silver dollars from Acapulco across the Pacific Ocean stopping at Guam on its way to Manila . Depositing its dollars in the Philippines , the ship then loaded trade goods from the East Indies for the return journey to New Spain . This round trip was essential to the maintenance of the Spanish Empire in the East Indies , which operated at an enormous financial loss only mitigated by the substantial subsidy from New Spain . Spanish dollars were the accepted currency across most of the East Indies , and disruption of this financial system could have profound effects on regional trade ; but British sailors had nevertheless been attacking the Manila galleons since Thomas Cavendish in 1587 .