The second flotilla, DDG-167 Shenzhen (back L) and FFG-570 Huangshan, will be replaced by FFG-529 Zhoushan （front R）and FFG-530 Xuzhou, which carry two helicopters and a Special Forces unit. The 3rd flotilla of Chinese naval fleet arrived in the waters of the Gulf of Aden off Somalia Thursday to carry out escort mission against pirates. [Xinhua]