On 9 May 1656, Jidu's armies attacked Kinmen (Quemoy), an island near Xiamen that Koxinga had been using to train his troops. Partly as a result of a major storm, the Manchus were defeated, and they lost most of their fleet in the battle. Koxinga had sent one of his naval commanders to capture Zhoushan island prior to Jidu's attack, and now that the Manchus were temporarily without an effective naval force in the Fujian area, Koxinga was free to send a huge army to Zhoushan, which he intended to use as a base to capture Nanjing.