While the July 24 notice does not mention China, it comes less than a year after Beijing unveiled several uncrewed maritime systems during a military parade, including the HSU-001 large underwater vehicle and the AJX-002 extra-large underwater vehicle. The HSU-001 is widely believed to be intended for lengthy intelligence, surveillance and reconnaissance missions. Analysts say no single technology has yet provided a complete answer to the problem of defending against underwater drones. Photo: CCTVThe service said underwater drones were becoming increasingly common in civilian and military operations because they could operate covertly for long periods. It warned they could be used for intelligence gathering, surveillance, smuggling, sabotage or attacks on ships and ports.