MANILA: The United States, Canada, Japan, and the Philippines conducted a two-day joint maritime exercise in Manila's exclusive economic zone in the South China Sea, the US Pacific Fleet said on its website on Monday. The maritime cooperative activity was aimed at "upholding freedom of navigation and overflight, reaffirming the four nations' commitment to bolstering regional security and stability," the US Pacific Fleet said. It involved four warships and a series of maritime manoeuvres to test and validate the interoperability of our armed forces' doctrines, tactics, techniques, and procedures, it added. In April, the Philippines conducted joint maritime activity with Japan, Australia, and the United States.