To ensure the safety of the merchant ships gathering at Macau in the winter of 1797 – 98 , the British commander in the East Indies , Rear @-@ Admiral Peter Rainier , sent a convoy to China escorted by the frigates HMS Sybille and HMS Fox and commanded by Captain Edward Cooke . After completing his mission Cooke decided to investigate the state of readiness of Spanish forces in Manila himself . He was also intrigued by reports that a ship carrying treasure was due to sail from Manila , which would make a valuable prize . Sailing in Sybille and accompanied by Captain Pulteney Malcolm in Fox , Cooke reached the Spanish capital on 13 January 1798 .