Anchored in Manila Bay , Cooke pretended that his ships were French vessels and successfully lured successive boatloads of Spanish officials aboard , taking them prisoner in turn . Once he had determined from his captives the state of defences in Manila , that the treasure ship had been unloaded at Cavite and that the Spanish squadron was undergoing extensive repairs and thus unavailable for operations , he sent a raiding party against a squadron of gunboats in the mouth of the Pasig River . Capturing the gunboats in a bloodless attack , Cooke then released his prisoners and sailed southwards , unsuccessfully assaulting Zamboanga before returning to Macau .